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

Abstract

AbstractChina 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 (0–20 cm) 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 (Pa), organic P (Po) compounds, and P fractions in soils were intensively assessed using chemical digestion, NaHCO3 extraction, 31P 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 43 mg·kg−1·yr−1. Pa was 67% higher after 3 years of IRCC, compared with RRD, but 78% lower after 10 years. Consecutive IRCC induced a decrease in Po compounds, with a mean decrease in TPo of approximately 20 mg·kg−1·yr−1. Long‐term consecutive IRCC increased transformation of Pa, Fe(II)–P, and Po into Ca–P and Fe(III)–P, increasing mean Ca–P and Fe(III)–P concentrations by approximately 69 and 7 mg·kg−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.