Influence of consecutive integrated rice-crayfish culture on phosphorus fertility of paddy soils

China has experienced an increase in integrated rice-crayfish (Procambarus clarkii) culture (IRCC) in rice paddies. However, whether the current regime degrades phosphorus (P) fertility in rice paddies remains unclear. To assess changes in P fertility, the surface soil (0-20cm) of high-yield rice paddies with 3, 6, and 10 consecutive years of IRCC was sampled in Honghu County in the Jianghan Plain region, China. Adjacent fields planted with long-term rotations of rice and dry-season crops (RRD) were also sampled. Total P (TP), available P (P-a), organic P (P-o) compounds, and P fractions in soils were intensively assessed using chemical digestion, NaHCO3 extraction, P-31 nuclear magnetic resonance, and sequential chemical extraction. IRCC significantly increased organic matter, total nitrogen, TP, Fe(II), and S2- contents of rice paddy soils and nutrient concentrations in the surface water, with a distinct decrease in total Fe and pH. Consecutive IRCC greatly influenced P fertility. Continuous P accumulation in rice paddy soils accelerated greatly, with a mean increase of approximately 43mgkg(-1)yr(-1). P-a was 67% higher after 3years of IRCC, compared with RRD, but 78% lower after 10years. Consecutive IRCC induced a decrease in P-o compounds, with a mean decrease in TPo of approximately 20mgkg(-1)yr(-1). Long-term consecutive IRCC increased transformation of P-a, Fe(II)-P, and P-o into Ca-P and Fe(III)-P, increasing mean Ca-P and Fe(III)-P concentrations by approximately 69 and 7mgkg(-1)yr(-1), respectively. Our results suggested that long-term consecutive IRCC degrades P fertility in rice paddies, and implementing IRCC in high-yield rice paddies is not recommended