Abstract
Excess dissolved organic nitrogen (DON) leaching occurs due to manure or fresh organic matter application coupled with high irrigation frequency in intensive greenhouse vegetable production systems (GVPS). Quantifying DON leaching is crucial in developing best management practices for intensive GVPS. The objectives of this study were to develop a DON leaching component for the water and N management model for greenhouse vegetables (WHCNS_veg) and to evaluate nitrate and DON leaching under different N management practices. Two seasons of tomato greenhouse experiments with several N management practices were conducted in Shouguang County, Shandong Province in China. The measured soil water content, soil nitrate and DON concentrations, and tomato yield were used to calibrate and evaluate the improved WHCNS_veg model. Results showed that the WHCNS_veg performed well in modeling soil water content, soil nitrate and DON concentrations, and tomato yield, giving normalized root mean square error values of 4.4%, 37.2%, 45.8% and 3.8%, respectively. Manure application significantly enhanced DON leaching, which accounted for 8.8% to 18.7% of the total N leaching under different N management practices. The simulated and measured tomato yield was not sensitive to different N management practices (except for the no N input treatment). However, the amounts of nitrate leaching, DON leaching, and N gas emission (NxO and NH3) under conventional N management were 2.1, 1.3, and 1.1-fold greater than those in the reduced N management treatment, respectively. Reduced N management practices should be recommended in the greenhouse tomato production in North China, which had a relatively high vegetable yield, less environmental impact, and more sustainability. Results indicated that the improved WHCNS_veg model has great potential to optimize N management and assess the environmental impact of GVPS.
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