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

Abstract

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.