Soil carbon and nitrogen of wheat-maize rotation system under continuous straw and plastic mulch

Straw and plastic mulching have been widely used in northwest China because of their ability to improve water use efficiency and increase grain yields. However, the dynamic changes of soil carbon (C) and nitrogen (N) under continuous straw and plastic mulching is rarely mentioned. A field experiment was conducted over four consecutive wheat (Triticum aestivum L.)-maize (Zea mays L.) rotation cycles in Northwest China to determine dynamic changes in soil C and N under three treatments: CK (traditional non-mulched), PM (transparent plastic mulching), and SM (straw mulching). Over the four wheat-maize cycles, soil organic carbon (SOC) in SM increased by 18% in the 0-0.2 m soil layer, while in PM SOC decreased by 15%, and in CK SOC changed little. Total N under CK and SM remained basically unchanged over time, but declined over time under PM. The overall microbial biomass carbon (MBC) and nitrogen (MBN) under SM increased by 32% and 17%, respectively, after four rotation cycles compared with significant decreases of 29% and 22% under PM and little change under CK. SM reduced soil temperature and increased soil water content, while PM increased both ST and water relation to the CK. Both SM and PM treatments increased grain yield and reduced nitrate N leaching. In the long run, straw mulching can improve SOC, MBC, MBN, and wheat-maize yield, and should be the recommended mulching practice for sustainable wheat-maize production in dryland areas in response to the potential challenges of climate change to dryland agriculture.