Abstract:
China is a major producer and consumer of vegetables, the large amount of application of nitrogen fertilizer is a crucial way for enhancing both the yield and quality of vegetables by farmers. However, excessive nitrogen input leads to low nitrogen use efficiency (NUE) in vegetable planting systems, which not only undermines agricultural productivity but also contributes to environmental issues such as soil degradation and water pollution. NUE serves as a key indicator for effective crop production, offering insights into practices that can minimize environmental impacts while maximizing output. Therefore, clarify the current NUEs of vegetable planting systems and its improving ways is imperative for sustainable agricultural practices. Despite its importance, current data on NUE in China's vegetable cultivation systems remains limited. Moreover, the factors influencing NUEs and potential measurement for NUE enhancement have not been thoroughly analyzed. Therefore, by collecting 1, 386 observations (1, 067 were from open-air and 319 were from greenhouse vegetable planting systems) from relevant field experiment literature during 2010 to 2020, we analyzed the NUE and its driving factors in China's current open-air vegetable systems and greenhouse systems, respectively. And a random forest model was applied to identify and rank the importance of different driving factors influencing nitrogen efficiency. Moreover, the effects of various management practices on NUE were quantitatively evaluated by meta-analysis method. Our findings indicated that the current average nitrogen application rates for open-air vegetable systems and greenhouse systems is 227.2(CI: 218.9-235.5) kg N ha
-1 and 361.5(CI: 336.8-386.1) kg N ha
-1 per growing season. Correspondingly, the NUE d in these two systems was 27.8% and 23.2%, with a range of 26.8-28.8% and 21.6-24.6%. respectively. Over all, the nitrogen application rate in greenhouse systems is 59.1% higher than in open-air systems, but the utilization rate is 16.8% lower. The results of the random forest analysis indicated that in the open-air systems, the nitrogen application rate contributed the most to NUE, at 24.0%, followed by sunlight duration during the growth period (10.7%), with soil TN content contributing the least, at only 2.9%. In the greenhouse systems, the nitrogen application rate was the highest contributing factor to the nitrogen fertilizer utilization rate, at 32.6%, followed by soil TP content (15.8%) and soil SOM content (11.4%), with soil pH contributing the least, at only 1.9%. Meta-analysis showed that combined application of phosphorus and potassium fertilizers is the most effective way to improve NUE in the open-air systems, followed by slow-release fertilizers, these two measures could enhance NUE by 82.4% and 53.0%, respectively. In greenhouse system, using urease and nitrification inhibitors could significantly improve NUE by 69.9%, then followed by reduction of nitrogen application (57.1%). Although current NUEs in vegetable planting systems in China was increased compared with other studies, efforts should continue to optimize nitrogen application rates and select comprehensive nitrogen management strategies based on the type of vegetables to improve NUE and mitigate environmental impacts in the future. The results of our study could provide data support and technical backing for the optimized management of nitrogen in vegetable cultivation systems.