ABSTRACT
Agricultural soil is a significant source of nitric oxide (NO). The primary aim of this study was to quantify the effect of long-term organic amendments on NO emissions from the summer maize-winter wheat cropping system in Guanzhong Plain. NO fluxes were regularly measured by the static chamber method for one year (June 2016 to June 2017). Field experiments included four fertilizer treatments that commenced in 1990. The control (CK, 0 kg·hm-2) treatment was unfertilized throughout the years. The fertilized treatments were synthetic fertilizer (NPK, 165 kg·hm-2), synthetic fertilizer plus maize stalk (NPKS, (165+40) kg·hm-2), and synthetic fertilizer plus dairy manure (NPKM, (50+115) kg·hm-2) during the winter wheat season. They were fertilized with synthetic fertilizer (188 kg·hm-2) during the summer maize season. The results showed small NO emission [<12.2 g·(hm2·d)-1] from the CK treatment within the experimental period. Large NO fluxes [up to 112.0 g·(hm2·d)-1 in NPK treatment] were captured following sowing and fertilization during the summer maize season and following fertilization during the winter wheat season for all fertilized treatments. Annual NO emissions and direct emission factors ranged from 0.13 to 0.57 kg·hm-2 and from 0.04% to 0.12%, respectively. Annual NO emissions from the NPKS and NPKM treatments were 17.6% lower and 68.0% (P<0.05) larger than those from the NPK treatment, respectively. Seasonal NO emissions from the NPKS and NPKM treatments were 41.1%-60.0% (P<0.05) lower than those from the NPK treatment during the winter wheat season, indicating that organic amendments reduced NO emissions. Seasonal NO emissions from the NPKS and NPKM treatments were 25.2%-292.1% (P<0.05) larger than that from the NPK treatment during the summer maize season, mostly due to the positive effect of soil organic matter content on NO emissions.
