High-P wheat straw increases the availability and turnover of phosphorus in lime concretion black soil

Objectives We investigated the effects of wheat straw with high and low phosphorus (P) contents on soil P availability, microbial biomass P (MBP), and the turnover of microbial biomass P, to provide a theoretical support for nutrient management under straw returning system.

Methods An incubation microcosm experiment was carried out using lime concretion black soil. The P content in high and low P wheat straws was 2.17, 0.51 mg/kg, respectively, from the plots of no fertilizer control and P application treatment in a long-term field experiment. The incubation experiment had three treatments–no straw control (CK), adding low-P wheat straw (LS), and adding high-P wheat straw (HS), and lasted 90 days under 70% of field water capacity at 25℃. Soil samples were collected at 0, 3, 7, 15, 30, 60, and 90 days of incubation for the determination of Olsen-P, inorganic P and organic P components, phosphatase activity, the number of phosphate solubilizing bacteria, soil microbial biomass P (MBP). The turnover characteristics of soil MBP were calculated.

Results The Olsen-P content in the three treatments increased within the first 15 days of incubation, and then kept stable. After 90 days of incubation, compared with CK, HS treatment significantly increased Olsen-P content by 59.4% but LS decreased that by 23.9% (P<0.05). The Ca₁₀-P and Fe-P in both HS and LS treatments were lower, while Ca₈-P were significantly higher than in CK. The Ca₂-P in HS treatment was significantly higher than those in LS and CK, while Ca₂-P in LS and CK were similar. Compared with CK, the labile organic P (LOP) and medium labile organic P (MLOP) in both LS and HS treatment were significantly enhanced but the medium stability organic P (MSOP) decreased, the high stability organic P (HSOP) content was similar in the three treatments. The LOP content in HS treatment was 37% and 158% higher than in LS and CK. Both HS and LS treatment stimulated the transformation of MSOP to LOP and MLOP, increased the number of organic and inorganic P-dissolving bacteria and soil phosphatase activity, increased the cumulative assimilation and mineralization, and the turnover intensity of soil MBP. HS had better effect than LS and resulted in shorter MBP turnover time.

Conclusions High-P-straw is more beneficial for the transformation of Ca₁₀-P and Fe-P to Ca₂-P and Ca₈-P, and the mineralization and turnover of microbial biomass P. Therefore, incorporation of high-P straw increase the availability of P in lime concretion black soil while low-P-straw incorporation decrease it.