Mulching Effects on Labile Soil Organic Nitrogen Pools under a Spring Maize Cropping System in Semiarid Farmland

Understanding the response of labile soil organic nitrogen (SON) pools to soil surface mulching is essential in identifying changes in soil N availability. Three treatments included non-mulched (CK), gravel-mulched (GM), and plastic film-mulched (FM), based on a 5-yr spring maize (Zea mays L.) field experiment in northwestern China. Compared with the CK, the GM and FM treatments significantly increased the grain yield and aboveground biomass, while had no effect on the soil organic carbon (SOC) and total nitrogen (TN) contents aft er 5 yr of this study. Compared with the CK, the GM and FM treatments significantly decreased light fraction organic N by 12.2 and 6.5 mg kg(-1), respectively, and extractable organic N by 7.7 and 9.3 mg kg(-1) in the 0- to 20-cm layer; while significantly increased water soluble organic N by 1.6 and 1.5 mg kg(-1) in the 0-to 20-cm layer, respectively, and by 1.3 and 1.2 mg kg(-1) in the 20- to 40-cm layer aft er 4 yr of this study. Meanwhile, the FM treatment significantly increased the microbial biomass N by 19.5 mg kg(-1) in the 0-to 20-cm layer compared with the CK aft er 4 yr of this study. In general, the GM and FM treatments increased maize productivity without detriment to the SOC and TN balance compared with the CK. The FM treatment displayed greater effects on enhancing crop yield and increasing labile SON pools than GM. It is suitable to choose plastic film mulching over gravel mulching to have increases in crop yields and improvements in soil N availability in semiarid farmland.