Release risk of soil phosphorus under different farming systems: Indoor experiments and in-situ measurement

Abstract

Agricultural phosphorus (P) application leads to the accumulation and release of soil P, which pose ecosystem risks. Different farming systems carry substantial risks of soil P release. This study evaluated the risk of soil P release in three representative systems of paddy fields in China (rice fields (RF), integrated crayfish-rice fields (CRF), and crayfish fields (CF)) using indoor adsorption and desorption experiments and the diffusive gradient in thin films (DGT) technique, and compared the obtained results. The soils of RF and CRF showed higher levels of redox potential (Eh), free Fe–Al oxides (DCB-Fe, DCB-Al), and amorphous Fe–Al oxides (Ox-Fe, Ox-Al) compared to CF. Additionally, the soils of CRF and CF exhibited higher total organic carbon (TOC) content. The indoor experiments revealed a positive correlation between the contents of Ox-Fe, Ox-Al, bioavailable P (BAP), clay, and soil P adsorption characteristics. Desorption characteristics were primarily influenced by total P, TOC, and Ox-Fe content. Furthermore, the order of soil P release risk followed CRF > RF > CF. According to the in situ DGT measurements, the soil P release fluxes were 0.266 mg·m−2·d−1 for CRF, 0.548 mg·m−2·d−1 for RF, and 0.583 mg·m−2·d−1 for CF. Accordingly, the risk of soil P release followed the order CRF < RF < CF. The contrasting results from these two methods are attributable to the indoor experiments indicating the potential for soil P adsorption under specific experimental conditions and the in situ DGT reflecting natural soil P release in a more effective and suitable manner for evaluating soil P release. The findings improve our understanding of the risk of soil P loss in CRF and provides valuable insights into the two methods.