Response of nitrous oxide emission to soil mulching and nitrogen fertilization in semi-arid farmland

Plastic film and gravel mulching have long been used to improve crop production, but few studies have focused on the effects of these mulching practices on nitrous oxide (N2O) emissions. Understanding the response of N2O emission to soil surface mulching is beneficial for improving management practices. We performed two field experiments over two years in northwestern China to measure the annual N2O emissions using the static chamber technique: first, we compared the N2O emissions from non-mulched (BP), gravel-mulched (GM) and plastic film-mulched (FM) maize (Zea mays L.) fields that received an equivalent nitrogen (N) application rate; second, we monitored the N2O emissions from film-mulched maize fields that received different N application rates [N applied at 0 (N0), 250 (N250) and 380 (N380) kg N ha−1]. Compared to the BP treatment, both the GM and FM treatments markedly improved the soil temperature and moisture, which significantly increased the maize yields and N uptake but did not increase the N2O emissions, most likely because the decreased soil mineral N content limited the N2O production. As a result, the yield-scaled N2O emissions were markedly reduced in the GM and FM treatments, and a greater reduction was observed in the FM treatment due to the higher grain yield. The N2O emissions persistently increased with an increasing N rate, but the grain yield peaked in the N250 treatment in which the N input was nearly equivalent to the maize N uptake. Consequently, low yield-scaled N2O emissions were obtained in the N250 treatment (125 and 155 g N2O-N Mg−1 grain in 2011-2012 and 2012-2013, respectively). Thus, we conclude that film mulching combined with an appropriate N input is a preferable management practice to improve the grain yield and to simultaneously minimize the direct N2O emission intensity in agriculture.