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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Agron.</journal-id>
<journal-title>Frontiers in Agronomy</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Agron.</abbrev-journal-title>
<issn pub-type="epub">2673-3218</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fagro.2022.989993</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Agronomy</subject>
<subj-group>
<subject>Hypothesis and Theory</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Evaluating the impact of biochar on biomass and nitrogen use efficiency of sugarcane using <sup>15</sup>N tracer method</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Chen</surname>
<given-names>Ge</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="author-notes" rid="fn003">
<sup>&#x2020;</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Gui</surname>
<given-names>Jie</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="author-notes" rid="fn003">
<sup>&#x2020;</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Qing</surname>
<given-names>Cui-Xian</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Huang</surname>
<given-names>Dong-Liang</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/858775"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Liao</surname>
<given-names>Fen</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Yang</surname>
<given-names>Liu</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1472368"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Guangxi Key Laboratory of Crop Genetic Improvement and Biotechnology, Guangxi Academy of Agricultural Sciences</institution>, <addr-line>Nanning</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Sugarcane Research Institute, Guangxi Academy of Agricultural Sciences, Key Laboratory of Sugarcane Biotechnology and Genetic Improvement (Guangxi), Ministry of Agriculture, Guangxi Key Laboratory of Sugarcane Genetic Improvement</institution>, <addr-line>Nanning</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>Edited by: Honghai Luo, Shihezi University, China</p>
</fn>
<fn fn-type="edited-by">
<p>Reviewed by: Prof. Dr. Amanullah, University of Agriculture, Pakistan; Jinyang Wang, Nanjing Agricultural University, China</p>
</fn>
<fn fn-type="corresp" id="fn001">
<p>*Correspondence: Fen Liao, <email xlink:href="mailto:gxliaofen@126.com">gxliaofen@126.com</email>; Liu Yang, <email xlink:href="mailto:yangliutibs@126.com">yangliutibs@126.com</email>
</p>
</fn>
<fn fn-type="equal" id="fn003">
<p>&#x2020;These authors have contributed equally to this work and share first authorship</p>
</fn>
<fn fn-type="other" id="fn002">
<p>This article was submitted to Plant-Soil Interactions, a section of the journal Frontiers in Agronomy</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>26</day>
<month>09</month>
<year>2022</year>
</pub-date>
<pub-date pub-type="collection">
<year>2022</year>
</pub-date>
<volume>4</volume>
<elocation-id>989993</elocation-id>
<history>
<date date-type="received">
<day>09</day>
<month>07</month>
<year>2022</year>
</date>
<date date-type="accepted">
<day>05</day>
<month>09</month>
<year>2022</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2022 Chen, Gui, Qing, Huang, Liao and Yang</copyright-statement>
<copyright-year>2022</copyright-year>
<copyright-holder>Chen, Gui, Qing, Huang, Liao and Yang</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>N is an essential nutrient for sugarcane (Saccharum spp. Hybribds) growth. Excess chemical nitrogen fertilizer applied still a serious problem of China sugarcane plant. Biochar has shown promise in improving crop yield and N use efficiency (NEU).However its impact on sugarcane is not well-studied. To investigate how biochar impacts on sugarcane growth and nitrogen N use efficiency (NUE), a glasshouse pot experiment was conducted using the <sup>15</sup>N tracer method. Two cultivars, GT11 and B8, were chosen as test objects and were planted under low N(120 kg N hm<sup>-2</sup>) and high N(600 kg N hm<sup>-2</sup>)condition, respectively. The effects of low and high biochar application rates (10 t hm<sup>-2</sup> and 20 t hm<sup>-2</sup>) on growth, nitrogen uptake, accumulation and distribution as well as NUE in GT11 and B8 were studied. Results showed that sugarcane biomass was not significantly affected by biochar application. N uptake by GT11 was significantly increased 23.91% - 45.42% by C20 and N120 condition at tillering stage and elongation stage. While N uptake by B8 showed a significant response to B10 and B20 with an increase of 27.27% and 30.40% at tillering stage,respectively. Biochar application led to 0.28% - 23.75% and 1.08% - 30.07% increase in NUE of GT11 and B8,respectively. The effect of biochar application of N from fertilizer(FF) was significant,however only C20 treatment shown remarkable response when under low N treatment. Our study suggest that the effects of biochar on sugarcane depend on varieties and the applied rate of biochar and N fertilizer.Biochar application with inorganic N could improve N uptake and N use of sugarcane.</p>
</abstract>
<kwd-group>
<kwd>biochar</kwd>
<kwd>nitrogen use efficiency</kwd>
<kwd>biomass accumulation</kwd>
<kwd>sugarcane</kwd>
<kwd>
<sup>15</sup>N isotope tracer</kwd>
</kwd-group>
<contract-num rid="cn001">2020YFD10006054-14</contract-num>
<contract-num rid="cn002">2019YFD1000503</contract-num>
<contract-num rid="cn003">31560353</contract-num>
<contract-num rid="cn004">2021GXNSFBA075010</contract-num>
<contract-num rid="cn005">GNK2021YT0110&amp;GNK2022JM14</contract-num>
<contract-sponsor id="cn001">National Key Research and Development Program of China<named-content content-type="fundref-id">10.13039/501100012166</named-content>
</contract-sponsor>
<contract-sponsor id="cn002">National Key Research and Development Program of China<named-content content-type="fundref-id">10.13039/501100012166</named-content>
</contract-sponsor>
<contract-sponsor id="cn003">National Natural Science Foundation of China<named-content content-type="fundref-id">10.13039/501100001809</named-content>
</contract-sponsor>
<contract-sponsor id="cn004">Natural Science Foundation of Guangxi Province<named-content content-type="fundref-id">10.13039/501100004607</named-content>
</contract-sponsor>
<contract-sponsor id="cn005">Guangxi Academy of Agricultural Sciences<named-content content-type="fundref-id">10.13039/501100015407</named-content>
</contract-sponsor>
<counts>
<fig-count count="0"/>
<table-count count="5"/>
<equation-count count="6"/>
<ref-count count="32"/>
<page-count count="11"/>
<word-count count="6633"/>
</counts>
</article-meta>
</front>
<body>
<sec id="s1">
<title>Highlight</title>
<list list-type="order">
<list-item>
<p>Biochar improve the biomass of sugarcane genotype with low NUE.</p>
</list-item>
<list-item>
<p>Biochar could increase the N uptake and N from fertilizer of sugarcane.</p>
</list-item>
<list-item>
<p>High biochar application improve sugarcane take more N from fertilizer.</p>
</list-item>
</list>
</sec>
<sec id="s2" sec-type="intro">
<title>Introduction</title>
<p>Biochar is a carbon-rich substance prepared under hypoxic or anaerobic, low temperature (&lt;800 &#xb0;C) conditions (<xref ref-type="bibr" rid="B14">Lehmann et&#xa0;al., 2005</xref>). Biochar has shown great application potential in soil improvement (<xref ref-type="bibr" rid="B24">Pan et&#xa0;al., 2021</xref>), crop yield increase (<xref ref-type="bibr" rid="B23">Omara et&#xa0;al., 2020</xref>), and environmental restoration (<xref ref-type="bibr" rid="B2">AliZahed et&#xa0;al., 2021</xref>; <xref ref-type="bibr" rid="B3">Ba&#x15f;er et&#xa0;al., 2021</xref>). It has received extensive attention from domestic and abroad researchers. Nitrogen is the primary nutrient element for crop production. Numerous studies have focused on the effects of biochar on the N utilization of soil and crops. The raw material source and preparation temperature of biochar will affect its ability to absorb nitrogen N (<xref ref-type="bibr" rid="B17">Liao et&#xa0;al., 2018</xref>), as well as the growth and N use efficiency of crops (<xref ref-type="bibr" rid="B26">Shanta et&#xa0;al., 2016</xref>; <xref ref-type="bibr" rid="B5">Egamberdieva et&#xa0;al., 2019</xref>; <xref ref-type="bibr" rid="B22">Olszyk et&#xa0;al., 2020</xref>). Biochar can increase the yield of corn (<xref ref-type="bibr" rid="B23">Omara et&#xa0;al., 2020</xref>), wheat (<xref ref-type="bibr" rid="B31">Zee et&#xa0;al., 2017</xref>), rice (<xref ref-type="bibr" rid="B10">Huang et&#xa0;al., 2014</xref>; <xref ref-type="bibr" rid="B1">Ali et&#xa0;al., 2020</xref>), and other crops (<xref ref-type="bibr" rid="B21">Lou et&#xa0;al., 2016</xref>; <xref ref-type="bibr" rid="B8">Haque et&#xa0;al., 2019</xref>; <xref ref-type="bibr" rid="B18">Li et&#xa0;al., 2021</xref>), and increase the utilization rate of N fertilizer. Its short-term effect is more evident under the condition of soil nutrient deficiency; however, its effect on increasing the yield of fertile soil is far from significant or even invalid (<xref ref-type="bibr" rid="B12">Jeffery et&#xa0;al., 2017</xref>; <xref ref-type="bibr" rid="B27">Vijay et&#xa0;al., 2021</xref>). <xref ref-type="bibr" rid="B9">Huang et&#xa0;al. (2019)</xref> experiment with biochar application on rice for six consecutive seasons; the N utilization rate increased by 7%&#x2013;11% only during the fifth and the sixth seasons, indicating that the application of biochar must be repeated for a long period of time to increase the internal N utilization and yield of rice. The impact of biochar on crop yield and N utilization varies with crop or biochar species, application amount, and time.</p>
<p>Guangxi, a major sugarcane planting province in China, accounts for more than 60% of the country&#x2019;s planting area and sugar production. The application of N fertilizer is an essential guarantee for increasing sugarcane yield and sugar content (<xref ref-type="bibr" rid="B19">Li et&#xa0;al., 2016</xref>). However, the current large-scale application of N fertilizer in sugarcane production has caused problems such as low fertilizer utilization, soil acidification, compaction, toxin accumulation, and reduced fertility (<xref ref-type="bibr" rid="B30">Zeng et&#xa0;al., 2020</xref>). Low N utilization efficiency of sugarcane is one of the main problems restricting the increase of sugarcane yield in China. Controlling or reducing the amount of N fertilizer application while continuously increasing sugarcane yield and minimizing the negative impact of excessive nitrogen fertilizer application has always been an important scientific issue for sugarcane-growing countries (<xref ref-type="bibr" rid="B4">Chandrasekaran et&#xa0;al., 2014</xref>; <xref ref-type="bibr" rid="B19">Li et&#xa0;al., 2016</xref>; <xref ref-type="bibr" rid="B25">Prasara et&#xa0;al., 2019</xref>). Previous studies have found that biochar can improve the root characteristics of the sugarcane seedlings and increase their root-shoot ratio (<xref ref-type="bibr" rid="B20">Liu et&#xa0;al., 2015</xref>). These effects may be related to the fact that biochar can increase soil pH, reduce N loss in the soil in the early and mid-term growth stages and promote the availability of nitrogen, phosphorus, and potassium in the soil (<xref ref-type="bibr" rid="B15">Liao et&#xa0;al., 2019a</xref>). However, these experiments are only the results of a single variety and a single nitrogen treatment and cannot fully reflect the effects of biochar on sugarcane growth and N utilization (<xref ref-type="bibr" rid="B16">Liao et&#xa0;al., 2019b</xref>). In this study, we selected two varieties with different nitrogen use efficiency and studied the effects of biochar on sugarcane growth, nitrogen absorption, cumulative distribution, and nitrogen utilization efficiency under different nitrogen treatment conditions using the <sup>15</sup>N tracer method to explore the effects of biochar on sugarcane growth and N utilization. The results provide theoretical and technical references for applying biochar in sugarcane production and reducing the dependence on nitrogen fertilizer.</p>
</sec>
<sec id="s3" sec-type="materials|methods">
<title>Materials and methods</title>
<sec id="s3_1">
<title>Test materials</title>
<p>The sugarcane genotypes, Guitang 11 (GT11, N-inefficient) and B8 (N-efficient), were provided by the Germplasm Resource Garden of Sugarcane Research Institute, Guangxi Academy of Agricultural Sciences. The preliminary test found that the nitrogen use efficiency of the two varieties differed by about 1.0 fold.</p>
</sec>
<sec id="s3_2">
<title>Experimental design and treatments combination</title>
<p>The pot experiment was conducted from February 2016 to February 2017 in the greenhouse at Sugarcane Research Institute, Guangxi Academy of Agricultural Science, Nanning, China. Plastic pots of 40 cm in diameter and 40 cm in height were used. Biochar at the rate of 0 g (C0, equivalent to 0 t hm<sup>-2</sup>), 70 g (C10, equivalent to 10 t hm<sup>-2</sup>), and 141 g (C20, equivalent to 20 t hm<sup>-2</sup>) per pot was mixed with soil (30 kg) and incubated. We applied <sup>15</sup>N labeled urea at two rates: 1.8 g (N120, equivalent to 120 kg hm<sup>-2</sup> nitrogen fertilizer) and 9.0 g per pot (N600, equivalent to 600 kg hm<sup>-2</sup> nitrogen fertilizer). Each treatment had six replicates. Two sugarcane plants were planted in each pot. we applied P fertilizer 3.0 g (equivalent to 450 kg P<sub>2</sub>O<sub>5</sub>&#xb7;hm<sup>-2</sup>) and potassium K fertilizer 2.0 g (equivalent to 225 kg K<sub>2</sub>O hm<sup>-2</sup>) to each pot, and all the fertilizers were applied only once as base fertilizer when sugarcane is planted. The biochar was mixed and incubated with the aired dry soil one day in advance. The germination, planting, and growth management of the seed stems were the same as the experiment by Liao et&#xa0;al. (2019).</p>
<p>The soil was collected from a depth of 0&#x2013;20 cm from the sugarcane test field of the Sugarcane Research Institute, Guangxi Academy of Agricultural Sciences. It is classified as Fe-leachi-Stagnic Anthrosols (Cooperative Research Group on Chinese Soil Taxonomy, CRGCST 2001) with a pH of 6.25, electrical conductivity of 42.12 mV, total C content of 0.72 g kg<sup>-1</sup>, organic matter content of 15.1 g kg<sup>-1</sup>, alkali-hydrolyzable nitrogen (N) of 91.23 mg kg<sup>-1</sup>, phosphorus (P) of 43.41 mg kg<sup>-1</sup>, and potassium (K) of 152.03 mg&#xb7;kg<sup>-1</sup>.Soil was aired dry and was broken up less than 5 cm with a rubber mallet.</p>
<p>The test biochar was produced from cassava stems using pyrolysis conditions described by Liao et&#xa0;al. (2019). The total C, N, and H of biochar were 67.4%, 0.8%, and 2.18%, respectively. The content of total phosphorus, and potassium were3.53, and 13.40 g&#xb7;kg<sup>&#x2013;1</sup>. We used <sup>15</sup>N-labeled urea (Shanghai Chemical Plant Ltd.) as the nitrogen fertilizer, with an abundance of 10.18% and a nitrogen content of 46%). Biochar was ground less than 2 mm before mixed and incubated with dry soil.</p>
</sec>
<sec id="s3_3">
<title>Plant yield contents</title>
<p>Samples of sugarcane were collected in three periods: the seedling period (four months after transplanting), the elongation period (seven months after transplanting), and the maturity period (12 months after transplanting). Three pots were collected for each treatment, and samples were classified according to roots, stems, dried leaves, and green leaves, and the fresh weight (FW) data were recorded simultaneously. Dried the collected materials at 60 &#xb0;Ctill to constant weight, recorded the dry weights (DW, g/pot). The dried samples were ground to determine the total nitrogen content and <sup>15</sup>N abundance.</p>
</sec>
<sec id="s3_4">
<title>Determination of plant N content, total N uptake and nitrogen use efficiency</title>
<p>The abundance of <sup>15</sup>N was determined using an isotope mass spectrometer (Thermo Fisher, Waltham, MA, USA). Total N was determined by VAP50 Kjeldahl meter (Gerhardt, K&#xf6;nigswinter, Germany). N uptake, Ndff (recovery percentage of plant-derived from <sup>15</sup>N-urea), N uptake from fertilizer, N uptake from the soil, and N use efficiency were calculated using the following equation (<xref ref-type="bibr" rid="B23">Omara et&#xa0;al., 2020</xref>):</p>
<disp-formula>
<mml:math display="block" id="M1">
<mml:mrow>
<mml:mtext>Total&#xa0;N&#xa0;uptake&#xa0;</mml:mtext>
<mml:mrow>
<mml:mo>(</mml:mo>
<mml:mrow>
<mml:mtext>TN&#xa0;uptake,&#xa0;g/pot</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
</mml:mrow>
<mml:mtext>&#xa0;=&#xa0;total&#xa0;N&#xa0;concentration&#xa0;in&#xa0;plant&#xa0;&#xd7;&#xa0;total&#xa0;plant&#xa0;DW</mml:mtext>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula>
<mml:math display="block" id="M2">
<mml:mrow>
<mml:mtext>% Ndff&#xa0;=&#xa0;</mml:mtext>
<mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mo>(</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mn>15</mml:mn>
</mml:mrow>
</mml:msup>
<mml:msup>
<mml:mrow>
<mml:mtext>N&#xa0;abundance&#xa0;in&#xa0;plant&#xa0;-&#xa0;background</mml:mtext>
</mml:mrow>
<mml:mrow>
<mml:mn>15</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mtext>N&#xa0;abundance</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
<mml:mtext>&#xa0;/&#xa0;</mml:mtext>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mo>(</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mn>15</mml:mn>
</mml:mrow>
</mml:msup>
<mml:msup>
<mml:mrow>
<mml:mtext>N&#xa0;abundance&#xa0;in&#xa0;fertilizer-&#xa0;background</mml:mtext>
</mml:mrow>
<mml:mrow>
<mml:mn>15</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mtext>N&#xa0;abundance</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
<mml:mo>;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mtext>&#xa0;where,&#xa0;the&#xa0;background</mml:mtext>
<mml:mrow>
<mml:mn>15</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mtext>N&#xa0;abundance&#xa0;=&#xa0;</mml:mtext>
<mml:mn>0.3663&#xa0;%</mml:mn>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula>
<mml:math display="block" id="M3">
<mml:mrow>
<mml:mtext>Ndff&#xa0;</mml:mtext>
<mml:mrow>
<mml:mo>(</mml:mo>
<mml:mrow>
<mml:mtext>mg/pot</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
</mml:mrow>
<mml:mtext>&#xa0;=&#xa0;Plant&#xa0;DW&#xa0;&#xd7;&#xa0;N&#xa0;content&#xa0;&#xd7;&#xa0;%&#xa0;Ndff</mml:mtext>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula>
<mml:math display="block" id="M4">
<mml:mrow>
<mml:mtext>N&#xa0;uptake&#xa0;from&#xa0;fertilizer&#xa0;</mml:mtext>
<mml:mrow>
<mml:mo>(</mml:mo>
<mml:mrow>
<mml:mtext>FF&#xa0;,&#xa0;%&#xa0;</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
</mml:mrow>
<mml:mtext>&#xa0;=&#xa0;Ndff&#xa0;</mml:mtext>
<mml:mrow>
<mml:mo>(</mml:mo>
<mml:mrow>
<mml:mtext>mg/pot</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
</mml:mrow>
<mml:mn>&#xa0;x&#xa0;100&#xa0;/&#xa0;plant&#xa0;TN&#xa0;uptake</mml:mn>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula>
<mml:math display="block" id="M5">
<mml:mrow>
<mml:mtext>N&#xa0;uptake&#xa0;from&#xa0;soil&#xa0;</mml:mtext>
<mml:mrow>
<mml:mo>(</mml:mo>
<mml:mrow>
<mml:mtext>FS&#xa0;,&#xa0;%</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
<mml:mo>=</mml:mo>
</mml:mrow>
<mml:mtext>&#xa0;(total&#xa0;N&#xa0;uptake&#xa0;-&#xa0;N&#xa0;uptake&#xa0;from&#xa0;fertilizer)&#xa0;&#xd7;&#xa0;100&#xa0;/&#xa0;plant&#xa0;TN&#xa0;uptake</mml:mtext>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula>
<mml:math display="block" id="M6">
<mml:mrow>
<mml:mtext>Nitrogen&#xa0;use&#xa0;efficiency&#xa0;</mml:mtext>
<mml:mrow>
<mml:mo>(</mml:mo>
<mml:mrow>
<mml:mtext>NUE,&#xa0;%</mml:mtext>
</mml:mrow>
<mml:mo>)</mml:mo>
</mml:mrow>
<mml:mtext>&#xa0;=&#xa0;N&#xa0;uptake</mml:mtext>
<mml:mo>&#xa0;</mml:mo>
<mml:mo>&#xd7;</mml:mo>
<mml:mn>100/N&#xa0;applied</mml:mn>
</mml:mrow>
</mml:math>
</disp-formula>
</sec>
<sec id="s3_5">
<title>Statistical analysis</title>
<p>All data were processed and analyzed using Excel 2007. SPSS19.0 statistical package program was used for the analysis of variance (SPSS Institute, USA). One-way snalysis of variance and the least significant difference test (LSD) were used to assess the statistical differences between the biochar treatments at N120 or N600 level. The level of significance was assessed by 0.05 probability level.</p>
</sec>
</sec>
<sec id="s4" sec-type="results">
<title>Results</title>
<sec id="s4_1">
<title>The effect of biochar and N fertilizer treatment on biomass of sugarcane</title>
<p>A considerable difference in the effect of biochar co-treatment with N fertilizer on the biomass of the two varieties was observed, as shown in <xref ref-type="table" rid="T1">
<bold>Table&#xa0;1</bold>
</xref>. Two varieties were significantly different in the DW of root (<italic>p</italic> = 0.005), stem (<italic>p</italic>&lt; 0.001), leaves (<italic>p</italic>&lt; 0.001), and total DW (<italic>p</italic>&lt; 0.001). The accumulation of sugarcane biomass was more affected by nitrogen application rate (<italic>p</italic>&lt; 0.001), with an exception as the root DW (<italic>p</italic> = 0.208). Biochar could increase the DW of GT11 under low nitrogen conditions (N120). Total DW was 73.05, 195.21, and 347.49 g/pot at tillering stage, elongation stage, and maturation stage without biochar application (C0), respectively. Compared with control C0, total DW increased by 1.38%&#x2013;16.28%, 4.98%&#x2013;17.41% (<italic>p&lt;</italic> 0.05) and 0.25%&#x2013;6.61% after C10 and C20 treatment, respectively. These were mainly due to DW increases in the stem, green leaf, and root. Biochar application, under N600 treatment, did not show any significant effect of increasing DW of GT11.</p>
<table-wrap id="T1" position="float">
<label>Table&#xa0;1</label>
<caption>
<p>Effects of biochar and N fertilizer treatment on dry weight(DW) of two sugarcane varieties.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Variety</th>
<th valign="top" align="center">N treatment</th>
<th valign="top" align="center">Growth stages</th>
<th valign="top" align="center">Biochar treatment</th>
<th valign="top" align="center">Root(g/pot)</th>
<th valign="top" align="center">Shoot(g/pot)</th>
<th valign="top" align="center">Green Leaves(g/pot)</th>
<th valign="top" align="center">Senescence leaves(g/pot)</th>
<th valign="top" align="center">Whole plant(g/pot)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">GT11</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">16.34a</td>
<td valign="top" align="center">27.08a</td>
<td valign="top" align="center">23.36a</td>
<td valign="top" align="center">6.27a</td>
<td valign="top" align="center">73.05a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">15.23a</td>
<td valign="top" align="center">26.77a</td>
<td valign="top" align="center">24.55a</td>
<td valign="top" align="center">7.51a</td>
<td valign="top" align="center">74.06a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">17.85a</td>
<td valign="top" align="center">31.71a</td>
<td valign="top" align="center">28.03a</td>
<td valign="top" align="center">7.34a</td>
<td valign="top" align="center">84.94a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">37.60a</td>
<td valign="top" align="center">112.51a</td>
<td valign="top" align="center">17.03a</td>
<td valign="top" align="center">28.07a</td>
<td valign="top" align="center">195.21b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">44.67a</td>
<td valign="top" align="center">117.79a</td>
<td valign="top" align="center">17.67a</td>
<td valign="top" align="center">24.80a</td>
<td valign="top" align="center">204.93ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">43.83a</td>
<td valign="top" align="center">140.60a</td>
<td valign="top" align="center">20.30a</td>
<td valign="top" align="center">24.47a</td>
<td valign="top" align="center">229.20a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">38.79a</td>
<td valign="top" align="center">235.46a</td>
<td valign="top" align="center">22.93a</td>
<td valign="top" align="center">50.30a</td>
<td valign="top" align="center">347.49a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">25.16b</td>
<td valign="top" align="center">241.41a</td>
<td valign="top" align="center">22.68a</td>
<td valign="top" align="center">59.12a</td>
<td valign="top" align="center">348.37a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">32.36ab</td>
<td valign="top" align="center">253.97a</td>
<td valign="top" align="center">20.19a</td>
<td valign="top" align="center">63.92a</td>
<td valign="top" align="center">370.45a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">11.93a</td>
<td valign="top" align="center">55.72a</td>
<td valign="top" align="center">63.60a</td>
<td valign="top" align="center">3.00a</td>
<td valign="top" align="center">134.26a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">9.53a</td>
<td valign="top" align="center">52.70a</td>
<td valign="top" align="center">60.24a</td>
<td valign="top" align="center">4.74a</td>
<td valign="top" align="center">127.21a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">15.63a</td>
<td valign="top" align="center">44.54a</td>
<td valign="top" align="center">54.90a</td>
<td valign="top" align="center">3.95a</td>
<td valign="top" align="center">119.02a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">38.67a</td>
<td valign="top" align="center">216.27a</td>
<td valign="top" align="center">41.37a</td>
<td valign="top" align="center">42.97a</td>
<td valign="top" align="center">339.27a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">43.13a</td>
<td valign="top" align="center">179.30a</td>
<td valign="top" align="center">35.73a</td>
<td valign="top" align="center">37.60a</td>
<td valign="top" align="center">295.77a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">40.30a</td>
<td valign="top" align="center">216.99a</td>
<td valign="top" align="center">36.60a</td>
<td valign="top" align="center">33.20a</td>
<td valign="top" align="center">327.09a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">35.05a</td>
<td valign="top" align="center">417.05a</td>
<td valign="top" align="center">47.77a</td>
<td valign="top" align="center">68.84a</td>
<td valign="top" align="center">568.71a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">42.89a</td>
<td valign="top" align="center">347.51a</td>
<td valign="top" align="center">52.16a</td>
<td valign="top" align="center">110.37a</td>
<td valign="top" align="center">552.94a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">47.93a</td>
<td valign="top" align="center">307.89a</td>
<td valign="top" align="center">27.38a</td>
<td valign="top" align="center">85.37a</td>
<td valign="top" align="center">468.57a</td>
</tr>
<tr>
<td valign="top" align="left">B8</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">12.42a</td>
<td valign="top" align="center">29.58a</td>
<td valign="top" align="center">29.03a</td>
<td valign="top" align="center">7.90a</td>
<td valign="top" align="center">78.93a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">12.85a</td>
<td valign="top" align="center">18.23b</td>
<td valign="top" align="center">36.09a</td>
<td valign="top" align="center">8.12a</td>
<td valign="top" align="center">75.29a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">13.26a</td>
<td valign="top" align="center">22.69ab</td>
<td valign="top" align="center">29.81a</td>
<td valign="top" align="center">8.40a</td>
<td valign="top" align="center">74.16a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">67.07a</td>
<td valign="top" align="center">134.36a</td>
<td valign="top" align="center">25.33a</td>
<td valign="top" align="center">32.83a</td>
<td valign="top" align="center">259.59a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">48.47b</td>
<td valign="top" align="center">132.79a</td>
<td valign="top" align="center">23.87a</td>
<td valign="top" align="center">52.20a</td>
<td valign="top" align="center">257.33a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">44.20b</td>
<td valign="top" align="center">122.77a</td>
<td valign="top" align="center">23.67a</td>
<td valign="top" align="center">25.13a</td>
<td valign="top" align="center">215.77a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">50.65a</td>
<td valign="top" align="center">191.77a</td>
<td valign="top" align="center">21.30a</td>
<td valign="top" align="center">63.52a</td>
<td valign="top" align="center">327.24a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">43.48ab</td>
<td valign="top" align="center">172.81a</td>
<td valign="top" align="center">20.71a</td>
<td valign="top" align="center">62.33a</td>
<td valign="top" align="center">299.33a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">39.21b</td>
<td valign="top" align="center">207.76a</td>
<td valign="top" align="center">24.61a</td>
<td valign="top" align="center">78.28a</td>
<td valign="top" align="center">349.86a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">9.36a</td>
<td valign="top" align="center">38.92a</td>
<td valign="top" align="center">58.81a</td>
<td valign="top" align="center">3.46a</td>
<td valign="top" align="center">110.55a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">7.92a</td>
<td valign="top" align="center">41.60a</td>
<td valign="top" align="center">54.71a</td>
<td valign="top" align="center">6.06a</td>
<td valign="top" align="center">110.29a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">8.15a</td>
<td valign="top" align="center">40.33a</td>
<td valign="top" align="center">58.60a</td>
<td valign="top" align="center">4.16a</td>
<td valign="top" align="center">111.24a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">52.33a</td>
<td valign="top" align="center">181.08b</td>
<td valign="top" align="center">40.07b</td>
<td valign="top" align="center">48.63a</td>
<td valign="top" align="center">322.11a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">48.50a</td>
<td valign="top" align="center">183.96b</td>
<td valign="top" align="center">40.63b</td>
<td valign="top" align="center">24.87b</td>
<td valign="top" align="center">297.96a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">50.70a</td>
<td valign="top" align="center">217.39a</td>
<td valign="top" align="center">47.83a</td>
<td valign="top" align="center">45.40a</td>
<td valign="top" align="center">361.32a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">34.54ab</td>
<td valign="top" align="center">278.75a</td>
<td valign="top" align="center">46.08a</td>
<td valign="top" align="center">115.52a</td>
<td valign="top" align="center">474.89a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">45.99a</td>
<td valign="top" align="center">267.49a</td>
<td valign="top" align="center">59.29a</td>
<td valign="top" align="center">117.38a</td>
<td valign="top" align="center">490.15a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">32.75b</td>
<td valign="top" align="center">319.98a</td>
<td valign="top" align="center">47.96a</td>
<td valign="top" align="center">108.78a</td>
<td valign="top" align="center">509.47a</td>
</tr>
<tr>
<td valign="top" colspan="9" align="left">F-values and significance level</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">Variety</td>
<td valign="top" align="center">.005</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">.054</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C treatment</td>
<td valign="top" align="center">0.527</td>
<td valign="top" align="center">0.551</td>
<td valign="top" align="center">0.635</td>
<td valign="top" align="center">0.331</td>
<td valign="top" align="center">0.718</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">N treatment</td>
<td valign="top" align="center">0.208</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C and N interaction(C &#xd7; N)</td>
<td valign="top" align="center">0.013</td>
<td valign="top" align="center">0.105</td>
<td valign="top" align="center">0.485</td>
<td valign="top" align="center">0.783</td>
<td valign="top" align="center">0.189</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>C0, 0 t hm<sup>-2</sup> biochar; C10, 10 t hm<sup>-2</sup> biochar; C20, 20 t hm<sup>-2</sup> biochar; N120,120 t hm<sup>-2</sup> N fertilizer; N600,600 t hm<sup>-2</sup> N fertilizer; Different letters within the columns show a significant difference between the treatments at P=0.05 according to the LSD test.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>After biochar was applied, the total DW of B8 was slightly higher than that of the control (C0), mainly under high nitrogen (N600) and high carbon (C20) conditions. Under this condition, the total DW of B8 was 111.24 g/pot, 361.32 g/pot, and 509.47 g/pot at tillering stage, elongation stage, and maturation stage, respectively, which were 0.63%, 12.17%, and 7.28% higher than that of C0 treatment, but did not reach a significant level of difference. These increases are mainly attributable to an enhancement in the stem and leaves DW.</p>
</sec>
<sec id="s4_2">
<title>Effects of biochar and N fertilizer treatment on nitrogen accumulation and distribution in sugarcane</title>
<p>As shown in <xref ref-type="table" rid="T2">
<bold>Table&#xa0;2</bold>
</xref>, the N accumulation in stems, green leaves, and senescence leaves of the two varieties was significantly different after treatment <italic>(p</italic>&lt; 0.001). Both carbon and N treatments significantly affected N accumulation in sugarcane stems, senescence leaves, green leaves, and whole plants (<italic>p</italic>&lt; 0.001), but there was no significant interaction between carbon and N treatments. Biochar treatment promoted the increase of nitrogen accumulation in stem, and leaves of both varieties at different growth stages.</p>
<table-wrap id="T2" position="float">
<label>Table&#xa0;2</label>
<caption>
<p>Effects of biochar and N fertilizer application on N uptake of two sugarcane varieties.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Variety</th>
<th valign="top" align="center">N treatment</th>
<th valign="top" align="center">Growth stages</th>
<th valign="top" align="center">Biohar treatment</th>
<th valign="top" align="center">Root(mg/g)</th>
<th valign="top" align="center">Shoot(mg/g)</th>
<th valign="top" align="center">Green Leaves(mg/g)</th>
<th valign="top" align="center">Senescence leaves(mg/g)</th>
<th valign="top" align="center">Whole plant(mg/g)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">GT11</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">87.10a</td>
<td valign="top" align="center">173.31a</td>
<td valign="top" align="center">368.81b</td>
<td valign="top" align="center">36.46b</td>
<td valign="top" align="center">665b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">85.25a</td>
<td valign="top" align="center">161.20a</td>
<td valign="top" align="center">427.63ab</td>
<td valign="top" align="center">44.74a</td>
<td valign="top" align="center">718ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">92.63a</td>
<td valign="top" align="center">191.73a</td>
<td valign="top" align="center">493.25a</td>
<td valign="top" align="center">46.87a</td>
<td valign="top" align="center">824a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">617.73b</td>
<td valign="top" align="center">2092b</td>
<td valign="top" align="center">453.99b</td>
<td valign="top" align="center">174.13a</td>
<td valign="top" align="center">3338b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">742.97ab</td>
<td valign="top" align="center">2381ab</td>
<td valign="top" align="center">505.46ab</td>
<td valign="top" align="center">177.70a</td>
<td valign="top" align="center">3807b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">869.16a</td>
<td valign="top" align="center">3152a</td>
<td valign="top" align="center">653.05a</td>
<td valign="top" align="center">179.52a</td>
<td valign="top" align="center">4854a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">279.95a</td>
<td valign="top" align="center">1505a</td>
<td valign="top" align="center">227.19a</td>
<td valign="top" align="center">231.80b</td>
<td valign="top" align="center">2244a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">172.44b</td>
<td valign="top" align="center">1522a</td>
<td valign="top" align="center">216.55a</td>
<td valign="top" align="center">306.96ab</td>
<td valign="top" align="center">2217a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">229.03ab</td>
<td valign="top" align="center">1626a</td>
<td valign="top" align="center">199.14a</td>
<td valign="top" align="center">356.23a</td>
<td valign="top" align="center">2410a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">73.44a</td>
<td valign="top" align="center">354.98a</td>
<td valign="top" align="center">1064a</td>
<td valign="top" align="center">16.43a</td>
<td valign="top" align="center">1509a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">56.34a</td>
<td valign="top" align="center">334.62a</td>
<td valign="top" align="center">1108a</td>
<td valign="top" align="center">26.89a</td>
<td valign="top" align="center">1526a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">101.98a</td>
<td valign="top" align="center">302.01a</td>
<td valign="top" align="center">1081a</td>
<td valign="top" align="center">28.89a</td>
<td valign="top" align="center">1514a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">708.38a</td>
<td valign="top" align="center">4536ab</td>
<td valign="top" align="center">1148ab</td>
<td valign="top" align="center">287.89a</td>
<td valign="top" align="center">6680ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">827.04a</td>
<td valign="top" align="center">3766b</td>
<td valign="top" align="center">1061b</td>
<td valign="top" align="center">288.83a</td>
<td valign="top" align="center">5943b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">887.30a</td>
<td valign="top" align="center">4994a</td>
<td valign="top" align="center">1242a</td>
<td valign="top" align="center">252.69a</td>
<td valign="top" align="center">7377a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">261.32a</td>
<td valign="top" align="center">2783a</td>
<td valign="top" align="center">467.74a</td>
<td valign="top" align="center">328.59a</td>
<td valign="top" align="center">3841a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">322.54a</td>
<td valign="top" align="center">2306a</td>
<td valign="top" align="center">561.01a</td>
<td valign="top" align="center">565.02a</td>
<td valign="top" align="center">3755a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">364.10a</td>
<td valign="top" align="center">2083a</td>
<td valign="top" align="center">226.28a</td>
<td valign="top" align="center">499.12a</td>
<td valign="top" align="center">3173a</td>
</tr>
<tr>
<td valign="top" align="left">B8</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">77.24a</td>
<td valign="top" align="center">156.92a</td>
<td valign="top" align="center">417.06b</td>
<td valign="top" align="center">53.27a</td>
<td valign="top" align="center">704b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">80.69a</td>
<td valign="top" align="center">101.50b</td>
<td valign="top" align="center">659.57a</td>
<td valign="top" align="center">54.88a</td>
<td valign="top" align="center">896a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">92.06a</td>
<td valign="top" align="center">128.31ab</td>
<td valign="top" align="center">634.14a</td>
<td valign="top" align="center">64.28a</td>
<td valign="top" align="center">918a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">997.03a</td>
<td valign="top" align="center">2207a</td>
<td valign="top" align="center">635.27a</td>
<td valign="top" align="center">276.13b</td>
<td valign="top" align="center">4116a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">782.05b</td>
<td valign="top" align="center">2423a</td>
<td valign="top" align="center">841.42a</td>
<td valign="top" align="center">443.02a</td>
<td valign="top" align="center">4489a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">769.04b</td>
<td valign="top" align="center">2319a</td>
<td valign="top" align="center">885.62a</td>
<td valign="top" align="center">242.11b</td>
<td valign="top" align="center">4216a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">302.10a</td>
<td valign="top" align="center">1061a</td>
<td valign="top" align="center">207.25a</td>
<td valign="top" align="center">370.64a</td>
<td valign="top" align="center">1941ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">280.89a</td>
<td valign="top" align="center">1019a</td>
<td valign="top" align="center">225.12a</td>
<td valign="top" align="center">368.78a</td>
<td valign="top" align="center">1893b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">274.39a</td>
<td valign="top" align="center">1253a</td>
<td valign="top" align="center">260.86a</td>
<td valign="top" align="center">520.17a</td>
<td valign="top" align="center">2308a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">64.90a</td>
<td valign="top" align="center">237.55a</td>
<td valign="top" align="center">949.47b</td>
<td valign="top" align="center">23.92a</td>
<td valign="top" align="center">1275b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">54.69a</td>
<td valign="top" align="center">246.86a</td>
<td valign="top" align="center">991.72b</td>
<td valign="top" align="center">43.93a</td>
<td valign="top" align="center">1337ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">60.51a</td>
<td valign="top" align="center">288.60a</td>
<td valign="top" align="center">1359a</td>
<td valign="top" align="center">31.05a</td>
<td valign="top" align="center">1740a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">901.78a</td>
<td valign="top" align="center">3676a</td>
<td valign="top" align="center">1301b</td>
<td valign="top" align="center">399.59a</td>
<td valign="top" align="center">6279a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">863.03a</td>
<td valign="top" align="center">3578a</td>
<td valign="top" align="center">1452b</td>
<td valign="top" align="center">225.41b</td>
<td valign="top" align="center">6119a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">959.32a</td>
<td valign="top" align="center">5003a</td>
<td valign="top" align="center">2052a</td>
<td valign="top" align="center">430.46a</td>
<td valign="top" align="center">8445a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">241.88a</td>
<td valign="top" align="center">1802a</td>
<td valign="top" align="center">501.00a</td>
<td valign="top" align="center">709.44a</td>
<td valign="top" align="center">3255a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">309.03a</td>
<td valign="top" align="center">1676a</td>
<td valign="top" align="center">652.63a</td>
<td valign="top" align="center">764.84a</td>
<td valign="top" align="center">3402a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">232.96a</td>
<td valign="top" align="center">2194a</td>
<td valign="top" align="center">576.46a</td>
<td valign="top" align="center">690.45a</td>
<td valign="top" align="center">3694a</td>
</tr>
<tr>
<td valign="top" colspan="9" align="left">F-values and significance level</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">Variety</td>
<td valign="top" align="center">.054</td>
<td valign="top" align="center">.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">.685</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C treatment</td>
<td valign="top" align="center">0.257</td>
<td valign="top" align="center">0.002</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">0.042</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">N treatment</td>
<td valign="top" align="center">0.116</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C and N interaction (C &#xd7; N)</td>
<td valign="top" align="center">0.162</td>
<td valign="top" align="center">0.148</td>
<td valign="top" align="center">0.521</td>
<td valign="top" align="center">0.821</td>
<td valign="top" align="center">0.159</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>C0,0 t hm<sup>-2</sup> biochar;C10, 10 t hm<sup>-2</sup> biochar; C20, 20 t hm<sup>-2</sup> biochar;N120,120 t hm<sup>-2</sup> N fertilizer; N600,600 t hm<sup>-2</sup> N fertilizer; Different letters within the columns show a significant difference between the treatments at P=0.05 according to the LSD test.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>The nitrogen accumulation of GT11 in the whole plant was between 665&#x2013;4854 mg/pot under low nitrogen conditions. Compared with C0 treatment, the N accumulation of GT11 increased by 7.97%&#x2013;45.42% after biochar application, while N accumulation of roots, stem, and leaves also increased 2.05%&#x2013;50.68% in each reproductive period. In particular, C20 treatment significantly increased the nitrogen accumulation of the whole plant in the tillering and elongation stages, which were 23.91% (<italic>p</italic>&lt; 0.05) and 45.42% (<italic>p</italic>&lt; 0.05) higher than the control (665 mg/pot and 3338 mg/pot), respectively. Green leaf nitrogen accumulation also increased by 33.74% (<italic>p</italic>&lt; 0.05) and 43.85% (<italic>p</italic>&lt; 0.05) compared with the control of 368.81 mg/pot and 453.99 mg/pot, respectively, while 50.68% (<italic>p</italic>&lt; 0.05) increase in stem and 40.70% (<italic>p</italic>&lt; 0.05) increase in roots were obtained mainly during the elongation stage.</p>
<p>Under high nitrogen condition, biochar application could boost the N accumulation in the whole plant. In GT11, N accumulation increased by 0.33%&#x2013;10.43% at the tillering and elongation stages but did not reach a significant difference level. These increases were mainly due to the growth of nitrogen accumulation in roots, stem, and leaves, especially under the C20 treatment in the elongation period. The nitrogen accumulation significantly increased by 25.26%, 10.10%, and 8.25% compared to the respective controls of roots (708.38 mg/pot), stem (4536.27 mg/pot), and leaves (1148.21 mg/pot).</p>
<p>The biochar effect on B8 showed a similar change trend as GT11. The accumulation of whole plant nitrogen of B8 increased by 2.43%&#x2013;45.23% at each growth stage after biochar was applied, irrespective of N treatment application. At the tilling stage, the nitrogen accumulation after biochar application significantly increased by 27.27%&#x2013;30.40%, compared with the control (704 mg/pot) at N120 conditions; however, it significantly increased by 36.47% after C20 treatment at N600 condition. Biochar treatment promoted the green leaf nitrogen accumulation of B8 by 8.62%&#x2013;58.15% at each growth stage. After C10 and C20 treatments, the green leaf nitrogen accumulation reached 634.14&#x2013;659.57 mg/pot and 841.42&#x2013;885.62 mg/pot in the tillering and elongation stages, which were significantly higher than C0 by 52.05%&#x2013;58.15% and 32.45%&#x2013;39.41%, respectively.</p>
</sec>
<sec id="s4_3">
<title>Biochar effect on N from soil and N from fertilizer</title>
<p>As shown in <xref ref-type="table" rid="T3a">
<bold>Table&#xa0;3A</bold>
</xref>, under high and low nitrogen condition without biochar application, the nitrogen in GT11 roots, stem, and leaves in each growth period, was chiefly came from the soil, accounting for 64.62%&#x2013;82.02%. While the nitrogen from fertilizer (FF) accounted for 17.98%&#x2013;35.38%. Under low nitrogen conditions, FF of GT11 was between 21.51%&#x2013;35.03%,which was lower than C0 treatment by 0.02% - 6.32%.The FF of GT11 after C20 treatment was between 43.60%&#x2013;69.34%,which was higher than C0 by 19.87% - 37.70%.Under high nitrogen conditions, biochar treatment significantly increased FF of GT11 roots, stem, and green leaves with the value between 53.44.22% - 68.87%,which was more than CO by 30.76-40.68%. Further, the value of FF with C10 treatment was higher than that with C20 treatment by 0.03% - 4.31%.</p>
<table-wrap id="T3a" position="float">
<label>Table&#xa0;3a</label>
<caption>
<p>Effects of biochar and N fertilizer treatment on FF and FS of GT11.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">Variety</th>
<th valign="top" rowspan="2" align="center">N treatment</th>
<th valign="top" rowspan="2" align="center">Growth stages</th>
<th valign="top" rowspan="2" align="center">Biochar treatment</th>
<th valign="top" colspan="4" align="center">FF (%)</th>
<th valign="top" colspan="4" align="center">FS ( %)</th>
</tr>
<tr>
<th valign="top" align="center">Root</th>
<th valign="top" align="center">Shoot</th>
<th valign="top" align="center">Green Leaves</th>
<th valign="top" align="center">Senescence leaves</th>
<th valign="top" align="center">Root</th>
<th valign="top" align="center">Shoot</th>
<th valign="top" align="center">Green Leaves</th>
<th valign="top" align="center">Senescence leaves</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">GT11</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">30.85b</td>
<td valign="top" align="center">33.58b</td>
<td valign="top" align="center">29.18b</td>
<td valign="top" align="center">23.73b</td>
<td valign="top" align="center">69.15a</td>
<td valign="top" align="center">66.42a</td>
<td valign="top" align="center">70.82a</td>
<td valign="top" align="center">76.27a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">24.53c</td>
<td valign="top" align="center">30.72c</td>
<td valign="top" align="center">26.44b</td>
<td valign="top" align="center">22.88b</td>
<td valign="top" align="center">75.47a</td>
<td valign="top" align="center">69.28a</td>
<td valign="top" align="center">73.56a</td>
<td valign="top" align="center">77.12a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">57.53a</td>
<td valign="top" align="center">66.34a</td>
<td valign="top" align="center">59.54a</td>
<td valign="top" align="center">43.60a</td>
<td valign="top" align="center">42.47b</td>
<td valign="top" align="center">33.66b</td>
<td valign="top" align="center">40.46b</td>
<td valign="top" align="center">56.40b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">27.79b</td>
<td valign="top" align="center">34.93b</td>
<td valign="top" align="center">29.70b</td>
<td valign="top" align="center">32.94b</td>
<td valign="top" align="center">72.21a</td>
<td valign="top" align="center">65.07a</td>
<td valign="top" align="center">70.30a</td>
<td valign="top" align="center">67.06a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">26.65b</td>
<td valign="top" align="center">35.03b</td>
<td valign="top" align="center">28.48b</td>
<td valign="top" align="center">30.51b</td>
<td valign="top" align="center">73.35a</td>
<td valign="top" align="center">64.97a</td>
<td valign="top" align="center">71.52a</td>
<td valign="top" align="center">69.49a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">59.43a</td>
<td valign="top" align="center">69.34a</td>
<td valign="top" align="center">63.13a</td>
<td valign="top" align="center">58.05a</td>
<td valign="top" align="center">40.57b</td>
<td valign="top" align="center">30.66b</td>
<td valign="top" align="center">36.87b</td>
<td valign="top" align="center">41.95b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">27.49b</td>
<td valign="top" align="center">28.84b</td>
<td valign="top" align="center">22.05b</td>
<td valign="top" align="center">26.69b</td>
<td valign="top" align="center">72.51a</td>
<td valign="top" align="center">71.16a</td>
<td valign="top" align="center">77.95a</td>
<td valign="top" align="center">73.31a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">25.91b</td>
<td valign="top" align="center">28.82b</td>
<td valign="top" align="center">21.51b</td>
<td valign="top" align="center">24.19c</td>
<td valign="top" align="center">74.09a</td>
<td valign="top" align="center">71.18a</td>
<td valign="top" align="center">78.49a</td>
<td valign="top" align="center">75.81a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">60.82a</td>
<td valign="top" align="center">66.14a</td>
<td valign="top" align="center">53.96a</td>
<td valign="top" align="center">52.45a</td>
<td valign="top" align="center">39.18b</td>
<td valign="top" align="center">33.86b</td>
<td valign="top" align="center">46.04b</td>
<td valign="top" align="center">47.55b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">26.13c</td>
<td valign="top" align="center">31.15b</td>
<td valign="top" align="center">25.37b</td>
<td valign="top" align="center">19.89b</td>
<td valign="top" align="center">73.87a</td>
<td valign="top" align="center">68.85a</td>
<td valign="top" align="center">74.63a</td>
<td valign="top" align="center">80.11a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">61.23a</td>
<td valign="top" align="center">66.81a</td>
<td valign="top" align="center">57.23a</td>
<td valign="top" align="center">33.22a</td>
<td valign="top" align="center">38.77b</td>
<td valign="top" align="center">33.19b</td>
<td valign="top" align="center">42.77a</td>
<td valign="top" align="center">66.78b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">56.92b</td>
<td valign="top" align="center">65.07a</td>
<td valign="top" align="center">56.13a</td>
<td valign="top" align="center">34.81a</td>
<td valign="top" align="center">43.08b</td>
<td valign="top" align="center">34.93b</td>
<td valign="top" align="center">43.87b</td>
<td valign="top" align="center">65.19b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">28.50b</td>
<td valign="top" align="center">35.38b</td>
<td valign="top" align="center">29.34c</td>
<td valign="top" align="center">31.14c</td>
<td valign="top" align="center">71.50a</td>
<td valign="top" align="center">64.62a</td>
<td valign="top" align="center">70.66a</td>
<td valign="top" align="center">68.86a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">60.33a</td>
<td valign="top" align="center">68.87a</td>
<td valign="top" align="center">63.88a</td>
<td valign="top" align="center">60.01a</td>
<td valign="top" align="center">39.67b</td>
<td valign="top" align="center">31.13b</td>
<td valign="top" align="center">36.12b</td>
<td valign="top" align="center">39.99b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">59.37a</td>
<td valign="top" align="center">66.65a</td>
<td valign="top" align="center">61.32b</td>
<td valign="top" align="center">57.09b</td>
<td valign="top" align="center">40.63b</td>
<td valign="top" align="center">33.35b</td>
<td valign="top" align="center">38.68b</td>
<td valign="top" align="center">42.91b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">23.70b</td>
<td valign="top" align="center">25.36b</td>
<td valign="top" align="center">17.98b</td>
<td valign="top" align="center">21.84b</td>
<td valign="top" align="center">76.30a</td>
<td valign="top" align="center">74.64a</td>
<td valign="top" align="center">82.02a</td>
<td valign="top" align="center">78.16a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">59.68a</td>
<td valign="top" align="center">65.93a</td>
<td valign="top" align="center">53.64a</td>
<td valign="top" align="center">53.44a</td>
<td valign="top" align="center">40.32b</td>
<td valign="top" align="center">34.07b</td>
<td valign="top" align="center">46.36b</td>
<td valign="top" align="center">46.56b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">59.65a</td>
<td valign="top" align="center">66.04a</td>
<td valign="top" align="center">53.55a</td>
<td valign="top" align="center">50.32a</td>
<td valign="top" align="center">40.35b</td>
<td valign="top" align="center">33.96b</td>
<td valign="top" align="center">46.45b</td>
<td valign="top" align="center">49.68b</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">Variety</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C treatment</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">N treatment</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C and N interaction (C &#xd7; N)</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>C0,0 t hm<sup>-2</sup> biochar;C10, 10 t hm<sup>-2</sup> biochar; C20, 20 t hm<sup>-2</sup> biochar;N120,120 t hm<sup>-2</sup> N fertilizer; N600,600 t hm<sup>-2</sup> N fertilizer; FF,N from fertilizer; FS, N from soil; Different letters within the columns show a significant difference between the treatments at P=0.05 according to the LSD test.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>Data from <xref ref-type="table" rid="T3b">
<bold>Table&#xa0;3B</bold>
</xref> show that the performance trend of B8, after biochar and nitrogen co-treatment, was similar to that of GT11. In the case of no nitrogen application (C0), the FF of B8 roots, stem, and leaves was between 18.94% to 31.23%, and FS was between 68.77%&#x2013;81.06%.Under N120 condition, C10 treatment could slightly increase the FF of B8 roots,stem and leaves by 0.16% - 2.07%. With C20 treatment, FF of B8 was increased up to 55.95-72.02% which was higher that C0 by 16.21% - 40.79%.FF of B8 increased corresponding to N fertilizer applied rates. When N fertilizer applied rate reached 600 kg hm<sup>-2</sup>,FF of B8 was between 53.17% - 72.03%,that was more 10.00% - 38.43% than C0 treatment. And also observed that FF of B8 with C10 treatment was higher than that with C20 treatment by 0.93% - 15.76%.</p>
<table-wrap id="T3b" position="float">
<label>Table&#xa0;3b</label>
<caption>
<p>Effects of biochar and N fertilizer treatment on FF and FS of B8.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">Variety</th>
<th valign="top" rowspan="2" align="center">N treatment</th>
<th valign="top" rowspan="2" align="center">Growth stages</th>
<th valign="top" rowspan="2" align="center">Biochar treatment</th>
<th valign="top" colspan="4" align="center">FF (% )</th>
<th valign="top" colspan="4" align="center">FS( %)</th>
</tr>
<tr>
<th valign="top" align="center">Root</th>
<th valign="top" align="center">Shoot</th>
<th valign="top" align="center">Green Leaves</th>
<th valign="top" align="center">Dried leaves</th>
<th valign="top" align="center">Root</th>
<th valign="top" align="center">Shoot</th>
<th valign="top" align="center">Green Leaves</th>
<th valign="top" align="center">Dried leaves</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">B8</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">24.12b</td>
<td valign="top" align="center">27.02b</td>
<td valign="top" align="center">25.00b</td>
<td valign="top" align="center">18.94b</td>
<td valign="top" align="center">75.88a</td>
<td valign="top" align="center">72.98a</td>
<td valign="top" align="center">75.00a</td>
<td valign="top" align="center">81.06a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">24.09b</td>
<td valign="top" align="center">28.86b</td>
<td valign="top" align="center">25.16b</td>
<td valign="top" align="center">19.36b</td>
<td valign="top" align="center">75.91a</td>
<td valign="top" align="center">71.14a</td>
<td valign="top" align="center">74.84a</td>
<td valign="top" align="center">80.64a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">56.16a</td>
<td valign="top" align="center">66.49a</td>
<td valign="top" align="center">58.62a</td>
<td valign="top" align="center">35.15a</td>
<td valign="top" align="center">43.84b</td>
<td valign="top" align="center">33.51b</td>
<td valign="top" align="center">41.38b</td>
<td valign="top" align="center">64.85b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">27.34b</td>
<td valign="top" align="center">31.23b</td>
<td valign="top" align="center">27.58b</td>
<td valign="top" align="center">25.82b</td>
<td valign="top" align="center">72.66a</td>
<td valign="top" align="center">68.77a</td>
<td valign="top" align="center">72.42a</td>
<td valign="top" align="center">74.18a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">25.84b</td>
<td valign="top" align="center">31.66b</td>
<td valign="top" align="center">29.65b</td>
<td valign="top" align="center">27.56b</td>
<td valign="top" align="center">74.16a</td>
<td valign="top" align="center">68.34a</td>
<td valign="top" align="center">70.35a</td>
<td valign="top" align="center">72.44a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">55.95a</td>
<td valign="top" align="center">72.02a</td>
<td valign="top" align="center">65.31a</td>
<td valign="top" align="center">60.50a</td>
<td valign="top" align="center">44.05b</td>
<td valign="top" align="center">27.98b</td>
<td valign="top" align="center">34.69b</td>
<td valign="top" align="center">39.50b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">27.97b</td>
<td valign="top" align="center">29.98b</td>
<td valign="top" align="center">20.22b</td>
<td valign="top" align="center">25.26b</td>
<td valign="top" align="center">72.03a</td>
<td valign="top" align="center">70.02a</td>
<td valign="top" align="center">79.78a</td>
<td valign="top" align="center">74.74a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">26.13b</td>
<td valign="top" align="center">29.13b</td>
<td valign="top" align="center">20.70b</td>
<td valign="top" align="center">24.02c</td>
<td valign="top" align="center">73.87a</td>
<td valign="top" align="center">70.87a</td>
<td valign="top" align="center">79.30a</td>
<td valign="top" align="center">75.98a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">63.68a</td>
<td valign="top" align="center">66.87a</td>
<td valign="top" align="center">57.38a</td>
<td valign="top" align="center">57.55a</td>
<td valign="top" align="center">36.32b</td>
<td valign="top" align="center">33.13b</td>
<td valign="top" align="center">42.62b</td>
<td valign="top" align="center">42.45b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">23.57c</td>
<td valign="top" align="center">28.40b</td>
<td valign="top" align="center">25.01b</td>
<td valign="top" align="center">18.28b</td>
<td valign="top" align="center">76.43a</td>
<td valign="top" align="center">71.60a</td>
<td valign="top" align="center">74.99a</td>
<td valign="top" align="center">81.72a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">59.54a</td>
<td valign="top" align="center">66.15a</td>
<td valign="top" align="center">58.53a</td>
<td valign="top" align="center">29.70a</td>
<td valign="top" align="center">40.46b</td>
<td valign="top" align="center">33.85b</td>
<td valign="top" align="center">41.47b</td>
<td valign="top" align="center">70.30a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">53.17b</td>
<td valign="top" align="center">66.16a</td>
<td valign="top" align="center">57.70a</td>
<td valign="top" align="center">28.28a</td>
<td valign="top" align="center">46.83b</td>
<td valign="top" align="center">33.84b</td>
<td valign="top" align="center">42.30b</td>
<td valign="top" align="center">71.72a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">26.74b</td>
<td valign="top" align="center">33.60c</td>
<td valign="top" align="center">30.69c</td>
<td valign="top" align="center">28.45c</td>
<td valign="top" align="center">73.26a</td>
<td valign="top" align="center">66.40a</td>
<td valign="top" align="center">69.31a</td>
<td valign="top" align="center">71.55a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">64.46a</td>
<td valign="top" align="center">72.03a</td>
<td valign="top" align="center">65.90a</td>
<td valign="top" align="center">62.20a</td>
<td valign="top" align="center">35.54b</td>
<td valign="top" align="center">27.97b</td>
<td valign="top" align="center">34.10b</td>
<td valign="top" align="center">37.80b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">58.77a</td>
<td valign="top" align="center">66.27b</td>
<td valign="top" align="center">62.01b</td>
<td valign="top" align="center">55.11b</td>
<td valign="top" align="center">41.23b</td>
<td valign="top" align="center">33.73b</td>
<td valign="top" align="center">37.99b</td>
<td valign="top" align="center">44.89b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">26.48b</td>
<td valign="top" align="center">29.69b</td>
<td valign="top" align="center">22.48c</td>
<td valign="top" align="center">26.00b</td>
<td valign="top" align="center">73.52a</td>
<td valign="top" align="center">70.31a</td>
<td valign="top" align="center">77.52a</td>
<td valign="top" align="center">74.00a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">63.94a</td>
<td valign="top" align="center">66.39a</td>
<td valign="top" align="center">57.88a</td>
<td valign="top" align="center">58.27a</td>
<td valign="top" align="center">36.06b</td>
<td valign="top" align="center">33.61b</td>
<td valign="top" align="center">42.12b</td>
<td valign="top" align="center">41.73b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">60.73a</td>
<td valign="top" align="center">66.90a</td>
<td valign="top" align="center">54.42b</td>
<td valign="top" align="center">55.81a</td>
<td valign="top" align="center">39.27b</td>
<td valign="top" align="center">33.10b</td>
<td valign="top" align="center">45.58b</td>
<td valign="top" align="center">44.19b</td>
</tr>
<tr>
<td valign="top" colspan="12" align="left">F-values and significance level</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">Variety</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C treatment</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">N treatment</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C and N interaction (C &#xd7; N)</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>C0,0 t hm<sup>-2</sup> biochar;C10, 10 t hm<sup>-2</sup> biochar; C20, 20 t hm<sup>-2</sup> biochar;N120,120 t hm<sup>-2</sup> N fertilizer; N600,600 t hm<sup>-2</sup> N fertilizer; FF,N from fertilizer; FS, N from soil; Different letters within the columns show a significant difference between the treatments at P=0.05 according to the LSD test.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>Statistical analysis showed that biochar and nitrogen treatment significantly affected the FF and FS of roots, stem, and leaves of the two varieties. There were significant differences between different treatment concentrations, and a significant interaction effect existed between biochar and nitrogen treatments.</p>
</sec>
<sec id="s4_4">
<title>Biochar effects on nitrogen use efficiency</title>
<p>As shown in <xref ref-type="table" rid="T4">
<bold>Table&#xa0;4</bold>
</xref>, the NUE of sugarcane was significantly influenced by biochar and nitrogen treatment (<italic>p&lt;</italic> 0.001). Variety mainly affected the NUE of green leaves (<italic>p</italic> = 0.002) and senescence leaves (<italic>p&lt;</italic> 0.001).All in all, Biochar and N fertilizer treatment could increase the whole plant NUE of GT11 and B8 in all growth stages and organs (roots, stem, and leaves).The NUE of GT11 was 0.17%-26.60% higher than that of CK at different growth stages and different organs, B8 also show 0.05%-30.07% higher than CK. Yet two varieties show different response to biochar and N fertilizer applied rate.</p>
<table-wrap id="T4" position="float">
<label>Table&#xa0;4</label>
<caption>
<p>Effects of biochar and N fertilizer treatment on N use efficiency of two sugarcane varieties.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Variety</th>
<th valign="top" align="center">N treatment</th>
<th valign="top" align="center">Growth stages</th>
<th valign="top" align="center">Biochar treatment</th>
<th valign="top" align="center">Root(%)</th>
<th valign="top" align="center">Shoot(%)</th>
<th valign="top" align="center">Green Leaves(%)</th>
<th valign="top" align="center">Senescence leaves(%)</th>
<th valign="top" align="center">Whole plant(%)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">GT11</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">3.20b</td>
<td valign="top" align="center">6.84b</td>
<td valign="top" align="center">12.62b</td>
<td valign="top" align="center">1.01b</td>
<td valign="top" align="center">21.54b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">2.51b</td>
<td valign="top" align="center">5.84b</td>
<td valign="top" align="center">13.31b</td>
<td valign="top" align="center">1.21b</td>
<td valign="top" align="center">20.45b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">6.31a</td>
<td valign="top" align="center">12.47a</td>
<td valign="top" align="center">24.17a</td>
<td valign="top" align="center">2.40a</td>
<td valign="top" align="center">45.29a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">2.52c</td>
<td valign="top" align="center">25.80a</td>
<td valign="top" align="center">15.85b</td>
<td valign="top" align="center">2.03c</td>
<td valign="top" align="center">47.40b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">12.11b</td>
<td valign="top" align="center">23.68a</td>
<td valign="top" align="center">16.94b</td>
<td valign="top" align="center">6.38b</td>
<td valign="top" align="center">53.16b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">18.17a</td>
<td valign="top" align="center">25.66a</td>
<td valign="top" align="center">34.82a</td>
<td valign="top" align="center">12.25a</td>
<td valign="top" align="center">74.00a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">9.05a</td>
<td valign="top" align="center">25.53a</td>
<td valign="top" align="center">7.28b</td>
<td valign="top" align="center">5.92b</td>
<td valign="top" align="center">51.65b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">5.26b</td>
<td valign="top" align="center">25.70a</td>
<td valign="top" align="center">8.78ab</td>
<td valign="top" align="center">5.48b</td>
<td valign="top" align="center">63.48a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">9.84a</td>
<td valign="top" align="center">31.61a</td>
<td valign="top" align="center">10.99ab</td>
<td valign="top" align="center">8.54a</td>
<td valign="top" align="center">51.92b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">0.45b</td>
<td valign="top" align="center">2.60b</td>
<td valign="top" align="center">6.34b</td>
<td valign="top" align="center">0.08a</td>
<td valign="top" align="center">8.46b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">0.81ab</td>
<td valign="top" align="center">5.26a</td>
<td valign="top" align="center">14.92a</td>
<td valign="top" align="center">0.21a</td>
<td valign="top" align="center">20.60a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">1.37a</td>
<td valign="top" align="center">4.64ab</td>
<td valign="top" align="center">14.34a</td>
<td valign="top" align="center">0.24a</td>
<td valign="top" align="center">19.98a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">4.74b</td>
<td valign="top" align="center">20.79b</td>
<td valign="top" align="center">7.92b</td>
<td valign="top" align="center">2.11b</td>
<td valign="top" align="center">48.47a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">11.73a</td>
<td valign="top" align="center">18.27ab</td>
<td valign="top" align="center">15.95a</td>
<td valign="top" align="center">4.07a</td>
<td valign="top" align="center">54.44a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">12.40a</td>
<td valign="top" align="center">23.51a</td>
<td valign="top" align="center">17.93a</td>
<td valign="top" align="center">2.96ab</td>
<td valign="top" align="center">54.80a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">2.58a</td>
<td valign="top" align="center">22.84a</td>
<td valign="top" align="center">6.56ab</td>
<td valign="top" align="center">3.31a</td>
<td valign="top" align="center">39.52b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">4.56a</td>
<td valign="top" align="center">25.02a</td>
<td valign="top" align="center">9.35a</td>
<td valign="top" align="center">7.09b</td>
<td valign="top" align="center">53.12a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">5.09a</td>
<td valign="top" align="center">25.91a</td>
<td valign="top" align="center">2.85b</td>
<td valign="top" align="center">6.81b</td>
<td valign="top" align="center">45.11ab</td>
</tr>
<tr>
<td valign="top" align="left">B8</td>
<td valign="top" align="center">N120</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">2.20a</td>
<td valign="top" align="center">4.97 b</td>
<td valign="top" align="center">12.25b</td>
<td valign="top" align="center">1.18b</td>
<td valign="top" align="center">18.18b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">2.26a</td>
<td valign="top" align="center">3.47b</td>
<td valign="top" align="center">19.48a</td>
<td valign="top" align="center">1.25b</td>
<td valign="top" align="center">23.36b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">1.83a</td>
<td valign="top" align="center">10.05a</td>
<td valign="top" align="center">21.80a</td>
<td valign="top" align="center">2.62a</td>
<td valign="top" align="center">36.33a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">9.65b</td>
<td valign="top" align="center">24.26a</td>
<td valign="top" align="center">20.52a</td>
<td valign="top" align="center">8.27a</td>
<td valign="top" align="center">64.22a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">9.52b</td>
<td valign="top" align="center">31.62a</td>
<td valign="top" align="center">29.31a</td>
<td valign="top" align="center">8.61a</td>
<td valign="top" align="center">71.65a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">12.65a</td>
<td valign="top" align="center">25.61a</td>
<td valign="top" align="center">27.33a</td>
<td valign="top" align="center">3.44b</td>
<td valign="top" align="center">65.30a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">9.93a</td>
<td valign="top" align="center">26.21b</td>
<td valign="top" align="center">11.03b</td>
<td valign="top" align="center">4.93a</td>
<td valign="top" align="center">56.87ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">8.65a</td>
<td valign="top" align="center">34.80a</td>
<td valign="top" align="center">10.35b</td>
<td valign="top" align="center">5.47a</td>
<td valign="top" align="center">52.88b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">10.25a</td>
<td valign="top" align="center">29.62ab</td>
<td valign="top" align="center">17.61a</td>
<td valign="top" align="center">7.04a</td>
<td valign="top" align="center">64.16a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">N600</td>
<td valign="top" rowspan="3" align="left">Tillering stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">0.36a</td>
<td valign="top" align="center">1.59b</td>
<td valign="top" align="center">5.58c</td>
<td valign="top" align="center">0.11b</td>
<td valign="top" align="center">6.76b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">0.77a</td>
<td valign="top" align="center">3.81a</td>
<td valign="top" align="center">13.63b</td>
<td valign="top" align="center">0.41 a</td>
<td valign="top" align="center">17.97a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">0.75a</td>
<td valign="top" align="center">4.47a</td>
<td valign="top" align="center">18.37a</td>
<td valign="top" align="center">0.22ab</td>
<td valign="top" align="center">23.13a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Elongated stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">5.59b</td>
<td valign="top" align="center">22.56a</td>
<td valign="top" align="center">9.41b</td>
<td valign="top" align="center">2.67b</td>
<td valign="top" align="center">42.87b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">13.10a</td>
<td valign="top" align="center">21.73a</td>
<td valign="top" align="center">22.50a</td>
<td valign="top" align="center">3.30b</td>
<td valign="top" align="center">58.70ab</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">13.26a</td>
<td valign="top" align="center">23.37a</td>
<td valign="top" align="center">20.97a</td>
<td valign="top" align="center">5.61a</td>
<td valign="top" align="center">61.90a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="3" align="left">Mature stage</td>
<td valign="top" align="center">C0</td>
<td valign="top" align="center">1.52b</td>
<td valign="top" align="center">12.57b</td>
<td valign="top" align="center">4.33b</td>
<td valign="top" align="center">2.66b</td>
<td valign="top" align="center">18.92b</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C10</td>
<td valign="top" align="center">4.66a</td>
<td valign="top" align="center">26.17a</td>
<td valign="top" align="center">10.48a</td>
<td valign="top" align="center">8.88a</td>
<td valign="top" align="center">48.99a</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="center">C20</td>
<td valign="top" align="center">3.33a</td>
<td valign="top" align="center">24.63a</td>
<td valign="top" align="center">9.09a</td>
<td valign="top" align="center">7.30a</td>
<td valign="top" align="center">46.48a</td>
</tr>
<tr>
<td valign="top" colspan="9" align="left">F-values and significance level</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">Variety</td>
<td valign="top" align="center">0.575</td>
<td valign="top" align="center">0.965</td>
<td valign="top" align="center">0.002</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">0.757</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C treatment</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">N treatment</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
<tr>
<td valign="top" colspan="4" align="left">C and N interaction (C &#xd7; N)</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">0.75</td>
<td valign="top" align="center">0.43</td>
<td valign="top" align="center">&lt;0.001</td>
<td valign="top" align="center">&lt;0.001</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>C0,0 t hm<sup>-2</sup> biochar;C10, 10 t hm<sup>-2</sup> biochar; C20, 20 t hm<sup>-2</sup> biochar;N120,120 t hm<sup>-2</sup> N fertilizer; N600,600 t hm<sup>-2</sup> N fertilizer; Different letters within the columns show a significant difference between the treatments at P=0.05 according to the LSD test.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>Under low nitrogen conditions (N120), the whole plant NUE of GT11 remarkably improved by C20 treatment at tillering and elongated stages. Compared with the C0 treatment, the whole plant NUE of GT11 increased from 21.54% and 47.40% to 45.29% and 74.00% at tillering and elongated stages after C20 treatment, respectively. Under N600 conditions, biochar just significantly improved the whole plant NUE at tillering stages. The whole plant NUE with C10 and C20 treatment was up to 20.60% and 19.98%, that was more than C0 treatment by 12.14% and 11.52%, respectively.</p>
<p>Data from <xref ref-type="table" rid="T4">
<bold>Table&#xa0;4</bold>
</xref> shows that the whole plant NUE of B8 was observably increased after biochar applied under N600 conditions. At tillering stage, the whole plant NUE was up to 17.97% and 23.13% from 6.76% by C10 and C20, respectively, and was up to 57.70% and 61.90% from 42.87% at elongated stage, and was up to 48.99% and 46.48% from 18.92% at mature stage. While under N120 conditions, biochar mainly significantly improved the whole plant NUE at tillering stage with C20 treatment.</p>
</sec>
</sec>
<sec id="s5" sec-type="discussion">
<title>Discussion</title>
<sec id="s5_1">
<title>Effects of biochar on sugarcane biomass</title>
<p>In accordance with previous report (Liao, 2019), biochar have little effect on the biomass accumulation of sugarcane. This is in agreement with some studies reported a decline in crop yield with biochar application (<xref ref-type="bibr" rid="B32">Zhu et&#xa0;al., 2014</xref>; <xref ref-type="bibr" rid="B11">Jay et&#xa0;al., 2015</xref>; <xref ref-type="bibr" rid="B22">Olszyk et&#xa0;al., 2020</xref>).Experiment on rice conducted by <xref ref-type="bibr" rid="B28">Xie et&#xa0;al. (2011)</xref> showed that grain yield decreased by 2% at first year after wheat straw biochar application. Previous researches seldom concern about different varieties yield response to the biochar impact. In this study, we found that the sugarcane variety GT11 with low NUE could significantly increase the biomass in the elongation period under low nitrogen treatment (N120), this is consistent with many studies which have shown that the effect of biochar on crop yield is not substantial in fertile soil; however, it becomes effective in poor soil (<xref ref-type="bibr" rid="B29">Xie et&#xa0;al., 2013</xref>; <xref ref-type="bibr" rid="B23">Omara et&#xa0;al., 2020</xref>; <xref ref-type="bibr" rid="B7">Haider et&#xa0;al., 2022</xref>). While the variety B8 with slightly higher NUE did not show a significant increase. We speculate that this difference arises from the differences in the response of different sugarcane genotypes to biochar. And this indicated that the impact of biochar on sugarcane yield is very complex.</p>
</sec>
<sec id="s5_2">
<title>Effects of biochar on nitrogen accumulation in sugarcane</title>
<p>The results from this study demonstrate that biochar could improve the nitrogen accumulation of the two sugarcane varieties under high and low nitrogen conditions, especially in the tillering and elongation stages, where the nitrogen accumulation of the whole sugarcane plant and green leaves significantly increased. Both biochar and nitrogen treatments greatly affected nitrogen accumulation in stem and leaves of the two varieties, but there was no significant interaction between them. These results are consistent with the effect of biochar on nitrogen accumulation in other crops. <xref ref-type="bibr" rid="B10">Huang et&#xa0;al. (2014)</xref> found that biochar promoted rice fertilizer nitrogen uptake by about 23%&#x2013;27%, thus increasing rice grain yield by 6%&#x2013;8%. <xref ref-type="bibr" rid="B13">Khan et&#xa0;al. (2021)</xref> also found that applying biochar under nitrogen reduction conditions can increase the nitrogen absorption of rice by 13%, thus increasing rice grain yield and NUE by 36% and 35%, respectively. Biochar can significantly increase nitrogen accumulation and the proportion of nitrogen obtained by crops from fertilizers or soil. This is probable due to biochar application can effectively improve soil structure, increase soil pH value, and facilitate the release of soil-available nitrogen and other nutrient availability (<xref ref-type="bibr" rid="B6">Frimpon et&#xa0;al., 2021</xref>). Our previous studies have also observed (<xref ref-type="bibr" rid="B17">Liao et&#xa0;al., 2018</xref>, 2019) that biochar can increase the nitrogen content in the soil and augment the soil nitrogen retention in the early growth stage of sugarcane, which could explain how biochar is capable of promoting the increase of nitrogen accumulation in the early growth stages of sugarcane.</p>
</sec>
<sec id="s5_3">
<title>The effect of biochar on sugarcane nitrogen use efficiency</title>
<p>Our experiment found that biochar can indeed improve the nitrogen utilization rate of sugarcane, where the NUE of roots, stem, and leaves increased to a certain extent. Under high and low nitrogen conditions, the nitrogen use efficiency of the whole plant, green leaves, and roots of GT11 was significantly improved, yet B8 got a huge boost under high nitrogen conditions. The positive influence of biochar on NUE is consistent with several reports. <xref ref-type="bibr" rid="B23">Omara et&#xa0;al. (2020)</xref> demonstrated that <italic>Zea mays</italic> L. grain yield, N uptake, and NUE increased by 25%, 28%, and 46%, respectively, with fertilizer N-biochar-combinations treatment compared to N fertilizer single treatment in sandy loam soil. <xref ref-type="bibr" rid="B30">Ye et al. (2020)</xref> conducted a three-year fixed-point experiment in stratospheric soil in Northeast China to study the effects of biochar and controlled-release of nitrogen fertilizers on rice yield, nitrogen use efficiency, residual nitrogen, and nitrogen balance in soil-crop systems. Their study found that yield and nitrogen use efficiency increased by 10.2% and 16.5%, respectively, after adding biochar. On the other hand, the experimental results showed that nitrogen accumulation, nitrogen use efficiency, and biomass in leaves were greatly improved, but biochar did not show a significant promoting effect on stem as harvested organs, suggesting that there is a complex transformation relationship in sugarcane &#x2018;source&#x2013;sink,&#x2019; thereby affecting the accumulation of stem biomass, which requires further research in later experiments.</p>
</sec>
</sec>
<sec id="s6">
<title>Conclusion</title>
<p>With consistent biochar treatments and growing conditions, two sugarcane varieties varied in response to biochar but with some general patterns. Results showed a positive effect of application of biochar in genotype with low NUE and low N condition. High biochar applied rate could effectively reduce the stress of high N level on the growth of sugarcane. However, this experiment is mainly a barrel planting experiment under greenhouse conditions, and many years of multi-pilot field experiments are still needed in the follow-up tests. Nonetheless, the effect of biochar treatment on the physiological and biochemical indicators of sugarcane will be carried out in the future, and the relationship between the nitrogen balance of the biochar&#x2013;sugarcane&#x2013;soil system will be studied to verify and evaluate the effect of biochar on the nitrogen absorption and utilization of sugarcane. Finally, this study provides a theoretical basis for biochar application in sugarcane cultivation and production.</p>
</sec>
<sec id="s7" sec-type="data-availability">
<title>Data availability statement</title>
<p>The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding authors.</p>
</sec>
<sec id="s8" sec-type="author-contributions">
<title>Author contributions</title>
<p>GC: Analyzed and interpreted the data, Wrote the original article. JG: Performed the experiments, Contributed reagents, materials, analysis tools or data. C-XQ: Contributed reagents, materials, analysis tools or data. D-LH: revised the article. FL: Conceived and designed the experiments, Performed the experiments, Wrote the original article. LY: conceived and design the experiments. All authors contributed to the article and approved the submitted version.</p>
</sec>
<sec id="s9" sec-type="funding-information">
<title>Funding</title>
<p>The present study was supported by National Key R&amp;D Program of China (2019YFD1000503, 2020YFD10006054-14), National natural science foundation of China (31560353), Natural Science Foundation of Guangxi Province (2021GXNSFBA075010), and Fund of Guangxi Academy of Agricultural Sciences (GNK2021YT0110,GNK2022JM14).</p>
</sec>
<sec id="s10" sec-type="acknowledgement">
<title>Acknowledgment</title>
<p>The authors would like to thank Editage (<uri xlink:href="http://www.editage.cn">www.editage.cn</uri>) for English language editing.</p>
</sec>
<sec id="s11" sec-type="COI-statement">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec id="s12" sec-type="disclaimer">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
</body>
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