[Effect of Long-term Organic Amendments on Nitric Oxide Emissions from the Summer Maize-Winter Wheat Cropping System in Guanzhong Plain].

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.

[Effects of Long-term Organic Amendments on Soil N2 O Emissions from Winter Wheat-maize Cropping Systems in the Guanzhong Plain].

The primary aim of this study was to quantify the effects of long-term organic amendments on soil nitrous oxide (N2O) emissions. Using static chamber-gas chromatograph technique, we measured N2O fluxes from winter wheat-maize rotation system and related environmental factors in the Guanzhong Plain for one year (October 2014 to October 2015). Field experiments were based on the "Chinese National Loess Fertility and Fertilizer Effects Long-term Monitoring Experiment". Four treatments were control (CK, 0 kg·hm-2), NPK (NPK, 353 kg·hm-2), NPK combined with maize straw[NPKS, (353+40) kg·hm-2] and cattle waste[NPKM, (238+115) kg·hm-2]. During the experimental period, N2O fluxes from CK treatment were small[<2.9 g·(hm2·d)-1]; while emissions from fertilized treatments peaked after fertilization[up to 113.4 g·(hm2·d)-1 for NPKS] and irrigation[up to 495.0 g·(hm2·d)-1 for NPKM] during winter wheat and maize seasons, respectively. N2O flux was significantly correlated to soil water-filled pore space for all treatments (r>0.28,P<0.05). Annual N2O emissions were (0.1±0.0), (2.6±0.1), (3.4±0.7) and (2.9±0.3) kg·hm-2 for CK, NPK, NPKS and NPKM, respectively. The fertilized treatments released higher N2O emissions than CK treatment (P<0.05), indicating that fertilization stimulated N2O emissions. However, the differences in N2O emissions were not significant among the fertilized treatments (P=0.06), suggesting that organic amendments did not increase N2O emissions obviously. The direct emission factors were 0.72%, 0.83% and 0.80% for NPK, NPKS and NPKM, respectively, all of which were lower than the IPCC default of 1%. The yield-scaled N2O emission for NPKM was the lowest among the fertilized treatments.