Optimizing nitrogen management to mitigate gaseous losses and improve net benefits of an open-field Chinese cabbage system.

The excessive and inappropriate application of nitrogen (N) fertilizer in open vegetable fields is a major anthropogenic source of gaseous N losses including nitrous oxide (NO) and ammonia (NH) emissions in China. A 2-yr Chinese cabbage (Brassica pekinensis L.) experiment was carried out to explore the impacts of optimized N management (reduced N application rate, controlled-release urea [CRF] and nitrification inhibitor [NI]) on cabbage yield, soil inorganic N, and NO and NH emissions, and to assess their economic benefits by a cost-benefit analysis. Six treatments including i) no N fertilizer (CK), ii) conventional urea fertilizer at 400 kg N ha based on farmers' practices (CN), iii) conventional urea at 320 kg N ha (RN), iv) conventional urea (320 kg N ha) with the addition of NI (RN + NI), v) CRF at 320 kg N ha (CR) and vi) CRF (320 kg N ha) with the addition of NI (CR + NI) were implemented in an open Chinese cabbage field. No significant differences were found in the cabbage yields and soil NH-N contents under different N fertilization treatments. Only CR + NI treatment had significantly lower soil NO-N contents than CN by 17.6%-34.6% at the early growing stages of cabbage in both years. Compared with CN, the NO emissions were significantly decreased by 8.61%, 34.4%, 37.8% and 46.6% under RN, RN + NI, CR and CR + NI, respectively, indicating that CR + NI favors NO abatement especially when NH has been suppressed by other 4 R practices. Meanwhile, the NH volatilization was 20.6% higher under RN + NI and 30.8% and 17.3% lower under CR and CR + NI compared to CN, respectively, which implied that CR was the most effective treatment in reducing the NH volatilization and total gaseous N loss in high NH-N loss scenarios. Moreover, the net benefit of RN decreased by $945 USD ha and those of RN + NI, CR and CR + NI treatments increased by $855, $930 and $1004 USD ha compared to CN, respectively. This study recommends CR + NI as the optimal N fertilizer management for the sustainable production of vegetables with the lowest environmental risks and the greatest economic benefits.