The regime and P availability of omitting P fertilizer application for rice in rice/wheat rotation in the Taihu Lake Region of southern China

In the Taihu Lake Region (TLR) of China, farmers' injudicious and excessive use of phosphorus (P) fertilizer has led to a dramatic spike in P accumulation. In view of that, the water flooding practice can increase soil P release and enhance P availability in rice season, compared with the strong P fixation in wheat season; it seems possible to save P fertilizer in rice season with the aim of reducing P loads without any crop yield declines. To validate this possibility, a 4-year pot experiment encompassing eight rice/wheat seasons and using four paddy soils with varying Olsen-P contents (6.16 to 40.95 mg kg(-1)) was conducted to compare rice/wheat yield, inorganic and organic P accumulation under four different P regimes, P fertilization for both rice and wheat (PR + W; conventional practice), P fertilization only for wheat (PW), P fertilization only for rice (PR), and no P fertilization for both seasons (Pzero). Compared with conventional PR + W treatment, PR treatment significantly decreased wheat yields, especially in medium- and low-P soils, with an Olsen-P concentrate decline of 34.4-62.8 %. In contrast, PW treatment showed no significant difference in the rice/wheat yields over 4 years irrespective of high-, medium-, and low-P-concentrated soils, despite the soil Olsen-P concentration declining by 34.9-64.4 %. This highlights the feasibility of omitting P fertilizer application to flooded rice for at least 4 years in rice/wheat cropping paddy fields while maintaining crop yields and reducing environmental risk. In four paddy soils, available inorganic P was the dominant effective P source and increased with the concentration of Olsen-P. Without P fertilization over time, the concentration of soil inorganic P fractions declined and organic P remained relatively constant. According to the P supply capacity of different soils under the regime of omitting P fertilization for rice, how to utilize the bioavailability of P in different P supply capacity soils when P fertilization is omitted for rice crops will be required in future work.