AUTHOR=Xiao Liang , Chen Guanglei , Wang Hong , Li Yixuan , Li Chi , Cheng Liang , Wu Wenge , Xiao Xin , Zhu Yiyong 

TITLE=Improvement of P Use Efficiency and P Balance of Rice–Wheat Rotation System According to the Long-Term Field Experiments in the Taihu Lake Basin

JOURNAL=Frontiers in Environmental Science

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2022.932833

DOI=10.3389/fenvs.2022.932833

ISSN=2296-665X

ABSTRACT=Phosphorus (P) accumulation in rice-wheat rotation fields around the Yangze River Delta are enriched during the last decades. To protect environment and save P resource, we conducted field experiments to optimize the P application scheme. 
First, one field experiment was designed as a series of P fertilizer application doses of 0~100 kg P2O5 hm-2. Grain yield and P uptake by crops were analyzed to calculate P surplus and P use efficiency. Soil P fractions were extracted and tested. According to the P balanc, we optimized fertilization by reducing chemical P  amount, which was used by local farmers, and further by substituting chemical P with organic fertilizer. To verify these managements, another field experiment was conducted with five treatments: no N, P, or K fertilizer (CK), only no P fertilizer (NK), farmers' fertilization of P (90 kg P2O5 hm-2) (FFP), reducing 20% P (FFP-20%P), reducing 20% P and replacing 20% P by manure (FFPM-36%P). 
The grain yield was enhanced by increased P fertilizer and reached at a constant level after 75 kg P2O5 hm-2. Moreover, the annual P surplus was balanced around the input of 150 kg P2O5 hm-2. Accordingly, optimization of fertilization  (FFP-20%P) and further by replacing of manure (FFPM-36%P) also achieve the equivalent crop yield like FFP treatment (90 kg P2O5 hm-2). Thus, 72~75 kg P2O5 hm-2 application rate is a threshold for production of rice and wheat and P balance. 
Total P content in soil was enhanced by increased input of P fertilizer and mainly divided in labile Pi and middle stable Pi fractions. Soil Olsen-P content increased by P fertilization accordingly. While the content of organic P and stable P content was relatively constant. Reducing P fertilizer by 20% had a similar results of soil P fractions, when compared with farmers’ P fertilization treatment.
Therefore, reducing at the least 20% current input of P by farmers (annual 180 kg P2O5 hm-2) according to the balance of P surplus in rice and wheat rotation systems is an imperative measure to guarantee crop production with enhanced P use efficiency, and meanwhile can alleviate environmental risk.