Effects of organic fertilizer incorporation practices on crops yield, soil quality, and soil fauna feeding activity in the wheat-maize rotation system

The decline in soil quality is becoming a significant process of soil degradation. Optimizing organic fertilizer incorporation practices in cropland is essential to enhancing crop productivity and soil health. However, that requires a comprehensive understanding of crop yield and soil quality reaction across an application gradient of organic fertilizer. We investigated the effect of organic fertilizer incorporation practices on crop yield, soil quality, and fauna feeding activity from fluvo-aquic soils on wheat (Triticum aestivum)-maize (Zea mays) rotation field. The six treatments included were unfertilized N control (UC), traditional chemical fertilizer application (TF, 600 N kg ha−1 year−1), and recommended chemical fertilization (RF, 400 N kg ha−1 year−1) with no organic fertilizer application rate, low-level 15.0 (RFLO), medium-level 30.0 (RFMO), and high-level 45.0 t ha−1 year−1 (RFHO) application, respectively. The research findings show that the yield with organic fertilizer incorporation treatments increased 26.4%–44.6% for wheat and 12.5%–40.8% for maize compared to RF plots. The long-term organic fertilizer incorporation rate increased organic carbon from 54.7% to 110.6% versus UC plots and 27.9%–74.0% versus chemical fertilizer (TF and RF) treatments, and the total nitrogen content of soil increased from 41.8% to 59.2%, and 24.6%–39.2%. The long-term inorganic fertilizer combined with organic fertilizer incorporation practices significantly enhanced soil sucrose (30.1%–51.9%), urease (28.4%–38.3%), and β-1,4-glucosidase (34.6%–122.4%) activity. Still, nitrite reductase, polyphenol oxidase, and catalase significantly lower 27.3%–49.9%, 8.5%–26.3% and 23.3%–34.3% than single applications of inorganic N fertilizer groups. Meanwhile, the results showed that organic fertilizer incorporation practices improved soil fauna feeding activity by 35.2%–42.5%, and the excessive application of inorganic N fertilizer reduced the activity level of soil fauna.


Introduction
Organic fertilizers are materials with defined chemical composition and high nutritional value that can provide adequate nutrients for plant growth (Moller and Schultheiss, 2015;Rajan and Anandhan, 2015). Organic fertilizers were mainly made by composting animal manure, human excrement, or plant matter (such as straw and garden waste) under microorganisms fermenting at high temperatures (Chew et al., 2019). Organic fertilizers improve the soil structure, provide a wide range of plant nutrients, and add beneficial microorganisms to the soil. Because of the benefits of organic fertilizers on soil structure and crop yield were widely used in the agricultural system (Brar et al., 2015;Maltas et al., 2018).
Organic fertilization practices can improve crop yields and soil quality, and combining organic and inorganic fertilizers was considered an effective solution to maintain the sustainability of crop ecosystems (Gentile et al., 2008). The application of organic fertilizers can not only improve soil structure and fertility, and increase soil organic carbon and other nutrients (Diacono and Montemurro, 2010;Liu et al., 2010). Many studies have shown that applying organic fertilizers to the soil surface can provide a rich food source for microorganisms and significantly increase microbial community composition and diversity compared to no application (Chang et al., 2007;Diacono and Montemurro, 2010). In addition, applying organic fertilizers significantly changes cation exchange capacity (CEC) and increases soil moisture content, causing changes in soil fauna community structure and composition in acidic soils (Zelles et al., 1992;Abbott and Murphy, 2007). Adding organic fertilizers benefits the formation and stability of earthworm communities due to the more stable nutrients in organic manure after aerobic fermentation (Bertrand et al., 2015). In contrast, others have found that long-term use of chemical fertilizers may reduce soil OM content and change the activity of soil biota, resulting in changes in soil microbial composition, and resulting in decreased soil invertebrates abundance and diversity due to environmental constraints and reductions in soil pH (Fauci and Dick, 1994;Davies et al., 2022). Wahyuningsih et al. (2019) show that the short-term applications of inorganic fertilizers (urea) significantly increased the soil fauna feeding activity after 2 days, compared to before the application. Tao et al. (2016) also show that soil organic matter (empty fruit bunch) plays an important role in soil ecosystem functioning by enhancing soil fauna feeding activity. Therefore, many studies have announced the effects of fertilization practice on soil nutritions, but the effects of inorganic combined with organic fertilizers on soil biota remain unclear.
In the wheat-maize rotation system, long-term fertilization is an essential factor affecting soil physicochemical properties and biota functions (Welbaum et al., 2004;Kaiser et al., 2007;Thomas et al., 2007;Miao et al., 2011;Chen et al., 2015b;Miller et al., 2020;Miner et al., 2020), and its response mechanism is mainly related to local climatic conditions, soil types, and fertilizer types (Lupwayi et al., 2011;Yu et al., 2015). Qaswar et al. (2020) and Gao et al. (2015) studies show that combining organic and inorganic fertilizers is one of the essential techniques to replace part of the inorganic chemical fertilizers and stabilize wheat and maize yield. Many studies have shown that replacing 20%-30% of chemical fertilizers with organic fertilizers can increase wheat-maize yields and improve soil availability and organic matter (Zhang et al., 2016b). Then, the applications of organic fertilizers were a relatively large range of variation, and the fresh weight of compost was generally from 10.0 to 35.0 t ha −1 (Hannet et al., 2021), and the application rate of dry matter of compost between 8.8 and 14.0 t ha −1 , but liquid manure up to 68.3 t ha −1 (Feng et al., 2013). This suggests the need for a better balance of the impact of fertilization with different organic fertilizer incorporation rates on the wheat-maize rotation system. Moreover, few have conducted long-term investigations of inorganic chemical fertilizers combined application of organic fertilizers with different incorporation rates for soil quality and health, including total soil carbon, organic carbon, nutrients, enzyme activities, and soil fauna activities.
The study aimed to determine the influence of inorganic combined with organic fertilizer incorporation practices (high, medium, and low levels) on crop yields, soil quality, and the fauna feeding activity on fluvo-aquic soil in north China.

Site description
The research treatments were set up starting in 2015 at Tianjin Experimental Farm (TEF), which is located in the suburbs of Tianjin, North China (39°28′N, 117°42′E, Supplementary Figure S1). The region belongs to a temperate monsoon climate, with an annual mean air temperature of 12.9°C and rainfall 586 mm, respectively (2015-2020) (Zhou et al., 2021). Rainfall is concentrated between July and September, with a tremendous annual variation. This soil was classified as fluvo-aquic soil, and the values of TN, OM, TP, and pH in soil (0-20 cm) were 0.82, 12.6, 0.80 and 8.1 g kg −1 , respectively.

Experimental design
The research treatments were conducted on a wheat-maize rotation system with the same cultivation and management practice from October 2019 to October 2020. In previous Frontiers in Environmental Science frontiersin.org 02 years, all wheat-maize straw was returned to the field following management practices. The six trial treatments of each area being 288 m 2 with three replicates, were established in 2015. The treatments included were unfertilized N control (UC), traditional chemical fertilizer application (TF, 600 N kg·ha −1 year −1 ), and recommended chemical fertilization (RF, 400 N kg·ha −1 year −1 ) with zero organic fertilizer (O) application rate, low-level 15.0 (RFLO), medium-level 30.0 (RFMO), and high-level 45.0 t ha −1 year −1 (RFHO) application, respectively. The recommended fertilization was based on the local soil characteristics and the crop target yield, combined with precision irrigation conditions (Cai and Qin., 2006;Yang et al., 2015). The recommended inorganic NPK fertilizers were urea (46.4% N), diammonium phosphate (18% N and 20.09% P), and potassium chloride (49.6% K), respectively (Zhou et al., 2021). In this study, inorganic nitrogen fertilizer was the limiting factor; when applying inorganic N fertilizer, simultaneously apply 200 kg ha −1 year −1 P and K fertilizer as base fertilizer. The organic fertilizer was produced through high-temperature fermentation of garden wastes and agricultural straw, by Xixing Fertilizer Technology Co., Ltd. (Shijiazhuang, China). The values of OM, TN, and TP in organic fertilizer were 86.6 ± 4.9, 6.18 ± 0.10, and 3.39 ± 0.07 g kg −1 , respectively (Zhou et al., 2021). The inorganic NPK rate in each wheat and maize season was half the annual application amount in six trial treatments, respectively. The application rates of fertilizers under different fertilization treatments was shown in Table 1. Two-thirds of the inorganic nitrogen fertilizer and the entire quantity diammonium phosphate and muriate potash fertilizer was applied when sowing as basal fertilizer, and one-third of nitrogen fertilizer is mainly used for top-dressing applications of wheat and maize, respectively. The organic fertilizer was applied to the soil surface by scattering before wheat sowing and incorporated into the topsoil by rotary tillage.

Field sampling and processing
The quadrat method determined the winter wheat yield by harvesting three 1 m 2 sampling areas per treatment (Lu et al., 2018). At the summer maize maturity stage, 20 plants were randomly selected from the middle row of each plot and harvested manually to determine the yield (Lu et al., 2018). The remaining crop was harvested mechanically.
Less than 1 week after harvest, three soil samples (each was a composite of five cores that formed one sample, 5.0 cm in diameter) were collected from each treatment at 20 cm depth on 24 October 2019 and 22 October 2020 to determine the chemical properties (Zhou et al., 2021). The chemical properties of soil were determined, including TC, TOC, TN, AN, TP, AP, TK, exchangeable Ca, Mg, K, Na concentrations, and CEC, EC, and soil pH values. The pH value and electric conductivity (EC) of the soil were measured with a glass electrode and extracted in a 1:2.5 soil/water (H 2 O) suspension after being allowed to stand for 30 min (Zhang et al., 2016b). The Dumas dry-combustion method analyzed all dry soil samples collected for total soil nitrogen (TC) and soil nitrogen (TN) contents using a PerkinElmer 2400 Series Ⅱ CHNS/O Analyzer (PerkinElmer Inc., Shelton, CT, United States). Soil total organic carbon (TOC) was determined using K 2 Cr 2 O 7 -H 2 SO 4 digestion. The alkaline hydrolysis diffusion method determined the available soil nitrogen (AN). The molybdenum blue colorimetrically determined the soil's total phosphorus (TP) content after extraction with a mixed acid solution of H 2 SO 4 and HClO 4 . Available phosphorus (AP) was determined colorimetrically after sodium bicarbonate extraction at pH 8.5. The content of total potassium (TK) in soil was determined by flame photometer  (Bao, 2008;Sunnemann et al., 2021). The concentrations of exchangeable Na, Mg, K, and Ca in soil were measured by ICP-OES (Agilent, 710 Series) after extraction with 1.0 mol L −1 ammonium acetate (Setia et al., 2013). The cation exchange capacity (CEC) was calculated with colorimetrically after using a hexamminecobalt (III) chloride extraction (ISO, 2018). Air-dried soil samples were sifted through a 2 mm sieve for soil enzyme activity determination. The six soil enzymes activity involved in C and N cycling were studied, including soil catalase, soil nitrite reductase, soil sucrase, soil urease, soil polyphenol oxidase, and soil β-1,4-glucosidase, and was determined spectrophotometrically with the soil enzyme kits provided by Suzhou Comin Biotechnology Company Limited (Suzhou, China) (Liu et al., 2018;Gao et al., 2019). Törne (1990) set up the bait lamina test for soil fauna feeding activity for soil environmental quality assessment. The bait lamina is made of polyvinyl chloride board (PVC board, gray), and the size by 120 mm × 6.0 mm × 1.0 mm (length × width × thickness) with a set of 16 double tapered holes (inner diameter 1.5 mm, outer diameter 2.0 mm) at the lower 85 mm, with the aperture spacing of 5 mm (Römbke et al., 2006). The standard feed for bait lamina filling usually consists of 70% cellulose (microparticles), 27% bran flakes (<500 mm), and 3% activated carbon (Eisenhauer et al., 2014). After filling double tapered holes with standard feed, insert the bait strip vertically into the soil, and the top hole was just below the soil surface (Supplementary Figure S2). In this study, soil fauna activities were measured from September 15 to 30 in 2019 and September 9 to 24 in 2020, respectively. Five test areas were set up for each treatment, and 5 strips per area were placed about 15-20 cm apart to monitor the feeding activities of soil fauna with 150 bait lamina in total. After 2 weeks of monitoring, the bait strips were taken from the soil and evaluated with filled (0), partly empty (0.5), and empty (1) (Vorobeichik and Bergman, 2021), to calculate the number of perforated bait strips at each study site and evaluate the percentage of perforated bait strips to the number of test holes in the field. In this study, soil temperature was measured using a HOBO U23-003 sensor (Onset Computer Corporation, Pocasset, MA, United States).

Statistical analysis
Statistical analysis used the Statistical Analysis System (SAS 9.2) software package and Origin Pro 2022 software. Analysis of variance and comparisons of means between treatments was determined using Duncan's multiple range test, and correlations between soil chemical properties were determined using Spearman's correlation coefficient analysis. Treatment impacts were reported to be significant at the 5% probability level.

Crop production
The grain yields of wheat and maize according to fertilization management practices are shown in Figure 1. Different fertilization management practices significantly affect wheat and maize yields, and there was no significant difference in the yield of wheat and maize between different years ( Table 2). The grain yields ranged from 0.68 to 6.35 t ha −1 for wheat and 5.40 to 9.77 t ha −1 for maize in 2018-2020. There was no difference in the wheat yields between different organic fertilizer (RFLO, RFMO, RFHO) incorporation and traditional fertilization (TF) treatments in 2018-2019, while the RFHO and TF significantly (p < 0.05) increased the maize yield by 34.7%, 36.6% as compared with RF, respectively. In 2019-2020, the medium and high organic fertilizer (RFMO, RFHO) incorporation and TF treatments increased the wheat yield by 36.4%, 50.6%, and 41.5% compared to RF, respectively (p < 0.05). There was no difference in wheat yields between RFMO, RFHO, and TF treatments. Similar to the 2018-2019 year, the RFHO and TF plots increased the maize yield by 47.2%, and 42.8% compared to RF, respectively (p < 0.05). Table 3 shows the soil chemical variables under each soil fertilizer management practice at 0-20 cm soil depth. Eleven variables were significantly affected by long-term inorganic combined with organic fertilizer incorporation practices compared with inorganic fertilizer plots (Table 3). The soil chemical parameters were significant correlations (Table 4). Organic fertilizer incorporation led to significant changes in total organic carbon (TOC) and total carbon (TC), levels of soil nutrients (Total N and P, Available N and P), and soil chemical properties of RFHO, RFMO, and RFLO plots, as compared to the RF and TF. The long-term organic fertilizer incorporation rate increased total organic carbon (TOC) from 54.7% to 110.6% versus unfertilized soil and 27.9%-74.0% versus chemical fertilizer treatments. TC content showed the same trend as TOC, increasing 19.5%-49.1% compared with UC and 17.2%-46.3% compared with RF. Soil total organic carbon (TC) and total organic carbon (TOC) increased positively under organic fertilizer plots with higher 2.2-6.0 g kg −1 for TC, and 2.4-6.4 g kg −1 for TOC than RF.

Soil physicochemical properties
The contents of total soil nitrogen (TN) and available nitrogen (AN) in the organic fertilizer incorporation plots increased significantly by 41. Compared with the UC, the fertilization treatment plots pH decreased by 0.49%-5.68%, while the organic fertilizer (RFLO, RFMO, RFHO) incorporation significantly reduced the pH by 3.40%, 5.44%, and 5.68% (p < 0.05), respectively. The content of exchangeable Ca in the organic fertilizer incorporation was significantly lower 10.05%, 7.64%, and 9.82%, than in the TF plots (p < 0.05). While no difference in the exchangeable Mg and CEC between different organic fertilizer (RFLO, RFMO, RFHO) incorporation and chemical fertilizer plots. The contents of exchangeable K and Na in the organic fertilizer incorporation plots significantly increased 49.4%-122.2%, and 21.4%-107.4%, compared with inorganic fertilizer. Figure 2 shows PCA for soil characteristics according to fertilization management practices. The PCA results show that the cumulative contribution of the first three principal components reached 84.7% (PC1: 62.9%; PC2: 13.8%; PC3: 8.0%; Supplementary Table S1).

Frontiers in Environmental Science frontiersin.org
This study significantly reduced soil fauna feeding activity in inorganic fertilizer plots. The feeding activities of soil fauna in the traditional fertilization (TF) and recommended fertilization (RF) site were lower than in all the other plots, about 24.6% in the RF site and 21.6% in the TF site ( Figure 3). We measured the highest average feeding activities in RFLO (35.2%), RFMO (46.8%), and RFHO (42.5%) compared with the other three investigation sites between 2019 and 2020. In RFLO, RFMO, and RFHO, adjoint with increased organic fertilizer incorporation, soil fauna feeding activities were significantly increased compared with RF and TF plots; however, the differences were not statistically significant in RFMO and RFHO plots. Furthermore, RFLO (31.9%) and RFMO (38.8%) in 2019, which had been treated additionally with organic fertilizer, showed higher feeding activities than UC (26.3%), but not significant. Throughout the 0-8 cm soil depth, the UC, RF, and TF treatments showed identical distributions, while RFLO, RFMO, and RFHO had consistent distribution trends (Figure 4). Compared with the organic fertilizer sites, feeding activities in RF and TF treatments showed that they rapidly decreased with increasing soil depth, compared with RFLO, RFMO, and RFHO, and reached a plateau after 4 cm. In the 0-6 cm layer soil depth, the soil fauna feeding activity in organic fertilizer plots was significantly higher compared with the UC and inorganic fertilizer plots (Figure 4).

Effect of organic fertilizer incorporation on crop yields
The results showed that compared with the recommended fertilization, the application of organic fertilizer significantly increased the yield of wheat (p < 0.05). Compared with the recommended fertilization (RF), the treatment of medium (RFMO) and low organic fertilizer (RFLO) had no significant influence on maize yield (p > 0.05), and the RFMO and RFLO plots were significantly lower than the high amount of organic fertilizer (RFHO) and the traditional fertilization treatment (TF). Similarly, Yang et al. (2014) reported that combinations of organic and inorganic nitrogen are likely to increase achievable yields and improve soil fertility with the wheatmaize system. This might be due to all organic fertilizers being used as base fertilizers in the wheat season, all chemical fertilizers being used in maize planting, and organic fertilizer incorporation into the soil, which increased soil OM contents, soil water availability, and aeration (Choudhary et al., 2018;Li et al., 2020). Welbaum et al.

FIGURE 3
Feeding activities (%) in the six fertilization management practices were determined by the bait-lamina test (n = 150 bait laminae) after 15 days of exposure in September 2019, and 2020. The data are median values, and the vertical bars represent SDs. Columns marked by different letters indicate significant differences at p < 0.05.

Frontiers in Environmental Science
frontiersin.org (2004) and Li et al. (2012) reported that when organic fertilizers incorporation can delay the senescence rate of crop roots and leaves, prolong the photosynthetic time of crops, increase the grain quality of ears by prolonging the grain filling time, and finally increase the yield. Studies have shown that the recommended fertilization amount requires good water and fertilizer management to maximize crop yield . The lower wheat yield in the recommended fertilization amount in this study may be caused by flood irrigation resulting in reduced plant availability of nitrogen (Li and Rao, 2003;Shang et al., 2015). The traditional fertilization (TF) could increase crop yields, indicating that inorganic N fertilizer input significantly affects crop yields; the soil organic fertilizers incorporation significantly affects TOC content and yields (Table 2). This result suggests that long-term studies were required to identify the effect of the inorganic combined with organic fertilizers on wheat-maize yield constraints and soil fertility.

Effect of organic fertilizer incorporation on soil chemical properties
The combined application of organic-inorganic fertilizers can provide quick-acting nutrients for crop growth, and effectively increase fertilizer efficiency and ensure the continuous supply of soil nutrients (Diacono and Montemurro, 2010). This study found that organic fertilizer incorporation benefited TC and TOC content, and medium and high levels (>30 t ha −1 year −1 ) significantly increased TC, and TOC contents compared to RF and TF treatment. The content of nitrogen (TN, AN) and phosphorus (TP, AP) in the organicinorganic fertilizers treatment was higher than in the no fertilizer treatment and chemical fertilizer treatment, the same trend as TC and TOC. Liu et al. (2015) and Cai and Qin (2006) research shows that organic fertilizer incorporation can increase TOC capacity by improving agricultural root biomass and exudates. Chen et al. (2015a) studies indicate that soil nutrient content increases after organic fertilizer  S-NiR, nitrite reductase; S-CAT, catalase; S-SC, sucrase; S-UE, urease; S-B-GC, β-1,4-glucosidase; S-PPO, polyphenol oxidase. Values are means ± SD. Means followed by the different lower case letters are significantly different at 5% level by Duncan's multiple range test.
Frontiers in Environmental Science frontiersin.org incorporation and the increase rate is mainly affected by the type and amount of organic fertilizer. Organic fertilizer incorporation increased crop yields, and soil organic matter and nutrient content were improved, consistent with the research of Gao et al. (2015) and Choudhary et al. (2018). The traditional mineral fertilizer (TF) significantly increased wheat and maize yields. Still, it did not have a significant influence on TC and TOC (p > 0.05), similar to the findings of Chen et al. (2015a) considered that the balanced application of inorganic fertilizers could keep farmers high, but it has a limited impact on soil carbon sequestration. Moreover, additional C, N, and P releases in the high-rate organic fertilizers could partly explain our findings. In addition, combined application of organic-inorganic fertilizers treatments increased exchangeable K, while the same treatments did not significantly increase the content of soil TK, relative to the UC and RF, consistent with the research of Hannet et al. (2021), indicating that potassium in the soil is not a limiting factor in alkaline soils. In this study, organic fertilizer incorporation significantly decreased soil pH and exchangeable Ca concentration, while exchangeable Na concentration and electrical conductivity increased in these plots compared with inorganic fertilizer. The pH of alkaline soil tends to decrease with the increase of commercial organic fertilizer application years, and the soil pH tends to be neutral, which is beneficial to the better growth of crops (Oyetunji et al., 2022). Demelash et al. (2014) reported increased Ca and Mg content with applying organic-inorganic fertilizers treatments, but it was not observed to increase the levels of other alkaline elements (K, Na). In this study, although the exchangeable Ca decreased, the exchangeable Na and K concentrations increased significantly. Organic fertilizer and soil type may be the main reasons for these differences (Abu Bakar et al., 2011;Manolikaki and Diamadopoulos, 2019;Jain and Kalamdhad, 2020). In this study, the cation exchange capacity (CEC) of soil increased by 4.9%-5.6% due to organic fertilizer incorporation; the same finding by Ouédraogo et al. (2001) and Cooper et al. (2020) studies that the increase in CEC with organic fertilizer application could be attributed to an increase in TOC. Still, it did not significantly affect (CEC) relative to the inorganic fertilizer plots in this study. It shows that based on stabilizing the wheat-maize yield, the soil quality of the wheat-maize planting area can be improved by combining organic and inorganic methods.

Effect of organic fertilizer incorporation on soil enzyme activity
Studies have shown that fertilization management and incorporation of organic matter can affect soil enzyme activity (Zhao et al., 2016;Li et al., 2017). Urease is closely related to soil nitrogen supply, and improving urease activity in the soil can convert organic nitrogen with high stability to available nitrogen (Zhang et al., 2016a). Therefore, the improvement of urease activity indicated that adding organic fertilizer incorporation improved soil nitrogen conversion. Li et al. (2010) and Wang et al. (2021) study found that soil catalase activity increased with more organic nitrogen, while Yang et al. (2018) showed no significant effect with the incorporation of cattle manure and biochar. The fertilization management practices decreased soil catalase, and nitrite reductase activity in this study may be caused by different soil types, organic fertilizer types and sampling time (Li et al., 2017). Soil sucrose and β-1,4-glucosidase reflects soil organic carbon accumulation and are an essential indicator of soil fertility (Zhang et al., 2016b;Ullah et al., 2019). The response of invertase and β-1,4-glucosidase to different fertilization practices was consistent with that of urease. The long-term addition of organic fertilizers significantly increased the activity of soil sucrose and β-1,4-glucosidase, mainly due to the soil organic carbon increase (Table 3). Polyphenol oxidase may suppress the synthesis of humic substances from phenolic intermediates produced during the mineralization of organic C, resulting in the accumulation of phenolic compounds (Wang et al., 2022). Applying organic fertilizers significant reduces the accumulation of phenolic substances and possible poisoning. In the long-term organic fertilizer incorporation plots, the decomposed organic matter provides sufficient energy and carbon source for soil microbial activities, accelerates the reproduction and growth of microorganisms, and improves soil physicochemical properties (Tiemann and Billings, 2011;Ai et al., 2012;Bowles et al., 2014). At the same time, organic fertilizer also contains many enzymes, which are beneficial to improve soil enzyme activity (Li et al., 2017). Therefore, the inorganic fertilizer combined with organic fertilizer incorporation practices can significantly increase the activities of urease (S-UE), sucrose (S-SC), and β-1,4glucosidase (S-B-GC) in the soil compared with the chemical fertilizer.

Effect of organic fertilizer incorporation on soil fauna feeding activity
This study found that soil fertilizer management influenced the feeding activities of soil fauna, and these responses were closely related to soil nutrition. Organic fertilizer application greatly enhanced soil fauna feeding activity, and then inorganic nitrogen fertilizer reduced the soil fauna feeding activity. The highest feeding activity rates were found in plots RFMO and RFHO with a larger amount of organic fertilizer incorporation practices, and traditional fertilization treatment (TF) had the lowest feeding activities Frontiers in Environmental Science frontiersin.org ( Figure 3). However, the feeding activity of soil fauna showed no significant differences between the control UC and inorganic fertilizer (RF and TF) plots. Studies have shown that the experimental time of using the Bait Lamina test is short, usually 3-15 days, and microorganisms cannot decompose and perforate organic matter in a short time, and nematodes, microarthropods such as earthworms, mites, enchytraeids, and collembolans was the main soil fauna causing bait perforation (Gongalsky et al., 2008;Birkhofer et al., 2011). Although some microorganisms are involved in feeding activities, the feeding activities is negligibly small compared to soil fauna (Gestel et al., 2003;Ashford et al., 2013). Applying organic fertilizers increased soil fauna feeding activities, which may be related to the changed soil fauna community's abundance and composition, leading to higher soil fauna feeding activity (Tao et al., 2016). This may explain why the highest feeding activity rates were found in plots RFMO and RFHO with a larger amount of organic fertilizer incorporation practices. The feeding activity of soil fauna in the inorganic fertilizer combined with organic fertilizer polts was high in the 0-6 cm depth range. Many studies show that feeding activities of soil fauna were strongly reduced from 4 to 8 cm soil layer in grassland and forest sites (Larade et al., 2012;Filzek et al., 2004;Gongalsky et al., 2008;Rożen et al., 2010). Other studies showed that soil fauna feeding activities were higher in the bottom of 5-8 cm soil layer than in topsoil layers at ryegrass and soybean fields (Marx et al., 2016;Mousavi et al., 2022). The long-term inorganic fertilizer combined with organic fertilizer incorporation practices significantly increased the soil fauna feeding activity, while the application of RFHO and RFMO did not significantly increase. Soil fertilizer management may affect soil fauna feeding activities by the soil chemical properties; meanwhile, the feeding activities of soil fauna affect the soil physicochemical properties by regulating the decomposition process of soil organic matter (Römbke et al., 2006;Briones and Schmidt, 2017). Geissen and Brummer (1999) research show a strong correlation between soil fauna feeding activities and chemical parameters, and fauna feeding activity increased with higher pH values in acid soil. In contrast, we found that the soils under organic fertilizer had the higher exchangeable K, Na, EC, nutrients (AN, AP), and TOC of all the management practices; however, the lowest pH and exchangeable Ca in alkaline soil (Table 3). The feeding activity of soil fauna was in organic fertilizer plots significantly higher than inorganic fertilized (RF and TF) plots and unfertilized (UC) plots. Soil water content and soil temperature are the main environmental factors affecting fauna feeding activities.
The feeding activity of fauna measured with the baitlaminae showed that the feeding activities increased with temperature (Gongalsky et al., 2008). Drought seriously affects the activities of invertebrates, especially earthworms that like moist soil (Eggleton et al., 2009). Törne (1990) research showed that in cracked clay with low moisture content in Germany, the percentage of bait bar perforation was between 4% and 16%. Precipitation explained the variation in feeding rates observed between 2019 and 2020 (Supplementary Figure S3).

Conclusion
We examined the effects of inorganic fertilizer combined with organic fertilizer incorporation practices on crop yields, soil quality, and fauna feeding activity. We showed that long-term inorganic fertilizer combined with organic fertilizer incorporation practices enhanced soil organic carbon, nutrition, and fauna feeding activity and significantly enhanced soil sucrose, urease, and β-1,4-glucosidase activity. Soil organic carbon, total nitrogen, and fauna activity showed a linear increase of 27.9%-74.0%, 24.6%-39.2%, and 35.2% %-42.5%, respectively, but the enzyme activity did not increase with the increase of organic fertilizer incorporation. In our studied area, the treatment of medium levels (30 t ha −1 year −1 ) may be recommended from crop yields and soil carbon sequestration. Our study findings have important significance for the application of organic fertilizer to the wheatmaize rotation systems.

Data availability statement
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding authors.

Author contributions
ZZ: data curation, formal analysis, writing-original draft, and writing-review and editing. SZ: data curation, formal analysis, and writing-review and editing. NJ: formal analysis, investigation. WX: investigation, validation, and writing-review and editing. JZ: conceptualization, funding acquisition, and writing-review and editing. DY: funding acquisition, methodology, writing review and editing, supervision.