Abstract
Excessive nitrogen fertilizer application in greenhouse vegetable production (GVP) is of scientific and public concern because of its significance to international environmental sustainability. We conducted a meta-analysis using 1174 paired observations from 69 publications on the effects of nitrogen fertilizer application and reducing nitrogen fertilizer application on the nitrogen losses on 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: nitrate leaching (+187.5%), ammonium leaching (+28.1%), total nitrogen leaching (+217.0%), nitrous oxide emission (+202.0%), ammonia emission (+176.4%), nitric oxide emission (+543.3%), yield (+35.7%) and nitrogen uptake (+24.5%). Environmental variables respond nonlinearly to nitrogen fertilizer application, with severe nitrate leaching and nitrous oxide emission when the application rate exceeds 570 kg N/ha and 733 kg/N, respectively. The effect of nitrogen fertilizer on yield growth decreases when the application rate exceeds 302 kg N/ha. Appropriate reduction in nitrogen fertilizer application rate substantially mitigates the environmental cost, for example, decreasing nitrate leaching (−32.4%), ammonium leaching (−6.5%), total nitrogen leaching (−37.3%), ammonia emission (−28.4%), nitrous oxide emission (−38.6%) and nitric oxide emission (−8.0%), while it has no significant effect on the nitrogen uptake and yield.
Highlights
China is the world’s largest vegetable producer [1,2] and greenhouse vegetable production (GVP) is a major vegetable cultivation system in China because of its higher economic benefits
The results indicated that the huge environmental cost caused by excessive nitrogen input could not be compensated with the little increased yield in Chinese GVP
Our results show a rapid increase in reactive nitrogen losses when the nitrogen fertilizer application exceeded the thresholds (570 kg N/ha for nitrate leaching, 733 kg N/ha for nitrous oxide)
Summary
China is the world’s largest vegetable producer (constituting ~50.5% of the world’s yield in 2016) [1,2] and greenhouse vegetable production (GVP) is a major vegetable cultivation system in China because of its higher economic benefits. Excessive nitrogen fertilizer application is especially common in GVP, which consumes about 40% of the total nitrogen input [5]. Due to its excessive nitrogen input, the nitrogen losses (e.g., nitrate leaching, greenhouse gas emission) are getting severe [6]. In northern China, the nitrate concentration of groundwater nearby vegetable greenhouses is much higher than other places [5]. Nitrous oxide is an important part of greenhouse gas despite its small share [8]. The average nitrous oxide emission factor of vegetable system in China is 0.69%, which is higher than other crop systems. The nitrous oxide emission in GVP is about 1.4 times than in open-field vegetable production [9]. In order to reduce the environmental cost, it is necessary to have a growing knowledge base about the multiple aspects of the effect of excessive nitrogen input [10]
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