Mitigation Options For N₂O Emissions From Spring Maize Soil In North China

Excessive nitrogen fertilizer application results in the lower nitrogen fertilizer use efficiency and cropland becomes an important source of N₂O emission. In order to increase the nitrogen fertilizer use efficiency, reduce the N₂O emissions, a field experiment was undertaken during spring maize growing season from 2007 to 2010 at Yuci, Shanxi Province, in North China, to investigate the effects of nine fertilizer treatments on N₂O emissions from spring maize soil, the responses of grain yield, in addition to N₂O emissions, were examined to explore feasible strategies to reduce N₂O emission. Low frequence of the manual measurement by static chamber may miss the N₂O peak emissions. During this research an automated measurement system was taken to improve the quality of N₂O monitoring. Based on the obersvered data to calibration and validation the Water and Nitrogen Management Model (WNMM) and add a mode to simulation the N₂O emission from sulfure coated urea to get the suitable option.The main results are as follows:1. Compared the effect of Traditional (T) to Optimal of nitrogen reduction treatments (O) on N₂O emission from 2007 to 2009. The results showed that the Optimal of nitrogen reduction treatment was a better choice, compare to Traditional treatment, produced the same yield of grain, and significantly reduced N₂O emissions by 48% on average every year, while reduce nitrogen fertilizer input by 64%. The WFPS and soil NH4+ content were identified as the major environmental factors controlling N₂O emissions from the soil every year. Banding with fertilizer should not during periods of heavy rainfalls and no irrigation immediately were devised as the feasible strategies to reduce N₂O emissions from spring maize in North China. N₂O uptake occurred mainly during the late stage of spring maize growth when the soil mineral N content was less than 46.4 mg kg^-1 soil.2. Study the effect of different nitrogen and phosphorus fertilizers on nitrous oxide emissions from spring-maize field in 2009. Four fertilization management practices were selected, viz. zero fertilizer as control treatment (CK), urea treatment (U), urea and phosphorus treatment (NP), nitric phosphate treatment (NOP). The results indicated that the emission factors of each treatment were U(0.55%),NP(0.4%) and NOP(0.27%) respectively. Compared to urea treatment not only urea and phosphorus could reduce the N₂O emissions, but also the nitric phosphate treatment could significantly reducing the N₂O emissions. NOP treatment was a better management practice in the sense that, when compared to U and NP treatments, it reduced not only N₂O emission by 42% and 26% separately, but also farmers'expenditure on fertilizers by 15% and 30%, while maintaining crop yield.3. Study the effect of different slow/control release nitrogen fertilizers on nitrous oxide emissions from spring maize field in 2009. Five fertilization management practices were selected, viz. (1) zero fertilizer application as control (CK), (2) urea (U), (3) sulfur-coated urea (SCU),(4) nitrate inhibitor dicyandiamide (DCD) with urea (UDD) and (5) DCD with ammonium bicarbonate (ADD), The results indicated that the N₂O emission factor (EF) of every fertilizer treatment was between 0.15%⁰.55%, lower than 1% which was suggested by the Intergovernmental Panel on Climate Change (IPCC). The sulfur-coated urea was most effective in reducing N₂O emissions, and the yield obtained under SCU was significantly higher than other four treatments (P<0.01). Nitrate inhibitor DCD was effective in reducing soil nitrification, which could significantly reduce N₂O emissions.4 Calibration and validation WNMM model and determining the BMPs based on the T and O treatments. The results indicated that the calibrated and validated WNMM model satisfactorily simulated soil mineral N contents, soil water content, soil temperature and N₂O emissions from the spring maize soil, compared with the field observations during calibration and validation. Results showed that the BMPs under normal fertilizer type were using nitric phosphate (73.75kg N hm^-2) as basal fertilizer and urea (129.92 kg N hm^-2) as banding with fertilizer, with irrigation of 100mm twice (one before tillage and one after banding with fertilizer).5. Add the SCU mode based on the field observed data under SCU treatment from 2009 to 2010 and the calibrated and validated WNMM model. The results showed that the S curve method was the best choice for the SCU mode, which had a significant relationship with all of the assessment index (P<0.05). Compared the performance of the four treatments (SCU, BMPs, T and O) under history 59 years weather data, and the results showed that the SCU performed better than BMPs, T and O treatments, which reduce N₂O emission from 21.8%～46.8%, increased yield from -0.48%～22.2% and net return from 1.8%～28.3%. So the sulfur coated urea was the best choice for the spring maize field in North China.