Nitrous Oxide Emissions and Net Greenhouse Effect from Spring-maize Field as Influenced by Combined Application of Manure and Inorganic Fertilizer

Nitrous oxide(N2O)is one of atmospheric greenhouse gases generated from dryland agro-ecosystems. Seeking its mitigation measures is a hot topic in global climate change studies. We investigated how the fertilizer application strategies could affect N2O emissions from the agricultural soils in the North China. The field experiment was conducted in Qianxi County, Hebei Province. Nitrous oxide fluxes were measured using static chamber-gas chromatography from November 2011 to November 2012 at the spring maize fields with four different treatments, i.e., chemical fertilizer(NPK), manure fertilizer(M), combined manure and chemical fertilizer(50%M +50% U), and Control(CK). The DNDC model, which was validated against data sets of N2O fluxes observed in the experiment, was used to estimate the net greenhouse effects of different management practices and their long term impacts on soil organic carbon(SOC)dynamics. Nitrous oxide emissions from the spring maize fields under different treatments had similar seasonal patterns, varying from-17.56 μg·m-2·h-1to 157.25 μg·m-2·h-1. Obvious N2O emission peaks were observed during the freeze-thaw period, with a maximum flux of 83.85 μg·m-2·h-1. The annual cumulative N2O emissions were 1.49, 1.20, 0.82 kgN·hm-2·a-1and 0.61 kgN·hm-2·a-1, and the N2O emitted during non-growing seasons was40.6%, 59.2%, 61.7% and 60.7% of the annual N2O emissions, for treatments NPK, 50%M+50%U, M and CK, respectively. Nitrous oxidefluxes had a significant positive correlation with soil moisture(WFPS)when WFPS ranged from 19% to 37%. However, there was no signifi- cant correlation between them when WFPS was from 37% to 70%. A significant positive correlation was found between N2 O fluxes and soil temperature(5 cm)under the conditions of suitable soil moisture and abundant substrate. Combined application of synthetic fertilizer and manure could reduce the net greenhouse effect by 33.5%, without decreasing crop yields. In addition, this treatment had positive effects on long-term SOC dynamics(50 years). It is concluded that implementation of manure amendments would effectively mitigate greenhouse gas emissions and increase the SOC in agro-ecosystem.