Straw application coupled with N and P supply enhanced microbial biomass, enzymatic activity, and carbon use efficiency in saline soil

Abstract Straw application is an efficient technology in saline soil improvement; however, the influence of nutrient (N and P) supply in this process on reclaiming saline land remains unclear. In the present study, N and P addition at different levels was thus employed in a wheat straw applied saline soil to investigate the responses of straw decomposition, soil enzymes (phosphatase, APA; β-glucosidase, BG; protease, PA; and urease, UA), and microbial carbon (C) use efficiency (CUE). In a 28-d soil incubation, five treatments were performed, i.e., ST, LO, MI, HI (representing straw with zero, low, medium, and high N and P inputs, respectively), and CK (without straw and nutrient). The results showed that straw decomposition and microbial biomass were significantly enhanced with the addition of N and P. The activities of APA, BG, PA, and UA increased to varying degrees, while the influence on biomass-specific activities changed with enzyme type under straw and nutrient application. Compared with ST, the addition of N and P decreased soil cumulative C levels in CO2 (CO2-C) evolution and microbial metabolic quotient (qCO2) by 4.1%–21.3% and 15.1%–38.9%, respectively. The values of CUE were in the following orders: MI > LO > HI ≈ ST at 14 d and LO > HI > MI > ST at 28 d, suggesting that N and P supply could increase CUE, but the effect on CUE could not enhance with increasing N and P input levels. Soil organic C contents were significantly positively correlated with the amount of straw decomposition and MBN, and significantly negatively correlated with qCO2. Hence, we suggest that adequate N and P supply may be an effective practice for increasing C sequestration in saline soil through straw application.