Greenhouse vegetable production is an important guarantee of food security in China, but the nitrogen loss caused by excessive application of nitroge n fertilizer in the production process has caused many environmental problems, such as soil acidification,groundwater pollution, greenhouse gas emissions and so on. The effect of fertilizer application on soil nitrogen loss in g reenhouse vegetable product ion is mostly carried out by the method of field control experiment, but less on the regional scale or larger scale. T his paper takes Shouguang City, Qingzhou City, Linzi District in Shandong Province and Cangnan County of Wenzhou City, Zhejiang Province a s the study area.
The purpose of this study is to study the effects of different nitrogen application models on nitrog en loss under different scales in greenhouse vegetable cultivation. It is hoped that this study can have theoretical and practical signifi cance for reducing nitrogen loss and realizing sustainable development in greenhouse vegetable
The main research results of this paper are as follows:
(1) The average content of soil available nitrogen in greenhouse vegetable planting area in recent ten y ears was from 132.98mg/kg in 2006 to 260.57 mg / kg in 2015 (an increase of 95.9 From 2006 to 2015, the content of soil available nitrogen in greenhouse vegetable planting area was significantly higher than that in non greenhouse vegetable field at the same time , about 29.7% higher than that in 2006 to 107.7% higher in 2015. From 2006 to 2010, the content of available nitrogen in greenhouse vegetable fields in Linzi District was mainly in the fourth and fifth levels,which means the application of nitrog en fertilizer was ineffective.
(2) The management models of different regions and di fferent vegetable species are obviously different. There are great differences in soil water content and soil nitrate content in the growth process of greenhouse vegetables under different management modes. The proportion of nitrogen leaching in Qingzhou g reenhouse tomato is about 58.3%, t he nitrogen leaching loss is 865.1kg N / ha, the gaseous loss is 28.5kg N / ha,and the nitrogen surplus was 81.1 kg N/ha. W H C N S_ve g simul ation results shows that with the increase of nitrogen application rate, nitrogen le aching loss and gas emission loss show s a linear increasing trend, but their effect on yield growth gradually decrease.
(3)Taking Linzi, Qingzhou and Shouguang as examples , the corresponding data were collected and the database of attribute data needed fo r the operation of WHCNS_veg model was established. The model was used to simulate the nitrogen loss of greenhouse tomato in autumn and winter under different soil types an d management models. The results showed that in the process of greenhouse tomato pla nting in autumn and winter, the nitrogen leaching loss in Linzi, Qingzhou and Shouguang area was about 15.8 × 10 3 t, accounting for 66.3% of the total nitrogen fertilizer in put, and the gas emission loss was about 0.696 × 10 3 t. It accounts for about 2.9% of the total nitrogen fertilizer input. Compared with the traditional nitrogen application rate of local farmers, the nitrogen application model with a 60% reduction in chemi cal fertilizer application had no effect on the yield of the whole region, bu t reduced the nitrogen leaching loss by 32.8% and the gas emission loss by 53.5%.
(4)We conducted a meta analysis using 1174 paired observations from 69 publications on the effec ts of nitrogen fertilizer application and reducing nitrogen fertilizer applic ation on the nitrogen losses in a broad scale. We found that the increase in nitrogen loss is much higher than that in production gain caused by excessive application of nitrogen fertilizer in comparison with non application: nitrate leaching (+187.5%), ni trous oxide emission (+202.0%), yield (+35.7%), and nitrogen uptake (+ We recommend 302 kg N/ha as an optimal nitrogen fertilizer application rate in terms of yield sustain ability and 570kg N/ ha as a warning application rate in terms of environmenta l sustainability. Compared with the excessive nitrogen fertilizer application in current situations, appropriate reduction in nitrogen fertilizer application rate substantially mi tigates the environmental cost, e.g. decreasing nitrate leaching (32.4%) and nitrous oxide emission ( 38.6%), while, it has no significant effect on the nitrogen uptake and yield. Considering current situation, 20% 40% reduction in nitrogen fertilizer app lication rate is appropriate in terms of both environment and yield.