Global greenhouse vegetable production systems are hotspots of soil N2O emissions and nitrogen leaching: A meta-analysis

Abstract

Vegetable production in greenhouses is often associated with the use of excessive amounts of nitrogen (N) fertilizers, low NUE (15-35%), and high N losses along gaseous and hydrological pathways. In this meta-analysis, we assess the effects of application rate, fertilizer type, irrigation, and soil properties on soil N₂O emissions and nitrogen leaching from greenhouse vegetable systems on the basis of 75 studies. Mean ± standard error (SE) N₂O emissions from unfertilized control plots (N₂O_control) and N leaching (NL_control) of greenhouse vegetable systems were 3.2 ± 0.4 and 91 ± 20 kg N ha^-1 yr^-1, respectively, indicating legacy effects due to fertilization in preceding crop seasons. Soil organic carbon concentrations (SOC) and irrigation were significantly positively correlated with NL_control losses, while other soil properties did not significantly affect N₂O_control or NL_control. The annual mean soil N₂O emission from fertilized greenhouse vegetable systems was 12.0 ± 1.0 kg N₂O-N ha^-1 yr^-1 (global: 0.067 Tg N₂O-N yr^-1), with N₂O emissions increasing exponentially with fertilization. The mean EF_N2O was 0.85%. The mean annual nitrogen leaching (NL) was 297 ± 22 kg N ha^-1 yr^-1 (global: 1.66 Tg N yr^-1), with fertilization, irrigation, and SOC explaining 65% of the observed variation. The mean leaching factor across all fertilizer types was 11.9%, but 18.7% for chemical fertilizer. Crop NUE was highest, while N₂O emissions and N leaching were lowest, at fertilizer rates <500 kg N ha^-1 year^-1. Yield-scaled N₂O emissions (0.05 ± 0.01 kg N₂O-N Mg^-1 yr^-1) and nitrogen leaching (0.79 ± 0.08 kg N Mg^-1 yr^-1) were lowest at fertilizer rates <1000 kg N ha^-1 yr^-1. Vegetables are increasingly produced in greenhouses, often under management schemes of extreme fertilization (>1500 kg N ha^-1 yr^-1) and irrigation (>1200 mm yr^-1). Our study indicates that high environmental N₂O and N leaching losses can be mitigated by reducing fertilization rates to 500-1000 kg N ha^-1 yr^-1 (mean: ∼762 kg N ha^-1 yr^-1) without jeopardizing yields.

Keywords: Greenhouse vegetable; Nitrogen leaching; Nitrogen use efficiency; Nitrous oxide emissions; Yield-scaled N losses.