Effect of 17 years of organic and inorganic fertilizer applications on soil phosphorus dynamics in a rice–wheat rotation cropping system in eastern China

Purpose: Fertilizer application can influence soil phosphorous (P) availability to crops. However, information is limited on the soil P transformation induced by application of fertilizer P in eastern China where most soils are inherently low in plant available P. The objective of this study was to investigate the long-term effect of various combinations of composted pig manure, rice straw, and inorganic fertilizers on the soil P pools, the subsequent P uptake by crops, and potential environmental effects. Materials and methods: A long-term fertilizer field trial was established on a silty clay loam in east China since 1996. The trial had six treatments: no fertilizer application, combination of inorganic fertilizers and rice straw, combination of inorganic fertilizers and organic manure, inorganic fertilizers only, rice straw only, and organic manure only. Soil samples (0–20 cm) were collected from each plot at the trial site in May 2013. Soil was analyzed for pH, organic matter, Olsen P, and Mehlich 3 P (M3 P). Hedley’s fractionation method was applied for P fractionation, and a soil P mass balance was evaluated. Results and discussion: The accumulation of total soil P (TP), Olsen P, and M3 P was most pronounced (p < 0.05) when inorganic fertilizer P was applied in combination with manure, while the use of straw instead of manure did not lead to such an increase. Recovery by plant biomass as a percentage of applied P was greater in plots with inorganic P fertilizer than plots treated with manure alone. Based on the results of P fractionation, residual fertilizer P accumulated mostly as moderately labile and sparingly labile forms of P, irrespective of the type of fertilizer P applied. Application of organic manure apparently prevented the conversion of applied fertilizer P into recalcitrant P forms and resulted in relatively larger proportions of available P. Conclusions: From both agronomic and environmental perspectives, combined application of inorganic fertilizer P and organic manure is a promising agronomic strategy for increasing soil P availability and reducing P loss from the rice–wheat rotation system.