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

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 N 2 O emissions and nitrogen leaching from greenhouse vegetable systems on the basis of 75 studies. Mean ± standard error (SE) N 2 O emissions from unfertilized control plots (N 2 O 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 N 2 O control or NL control. The annual mean soil N 2 O emission from fertilized greenhouse vegetable systems was 12.0 ± 1.0 kg N 2 O–N ha⁻¹ yr⁻¹ (global: 0.067 Tg N 2 O–N yr⁻¹), with N 2 O 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 N 2 O emissions and N leaching were lowest, at fertilizer rates <500 kg N ha⁻¹ year⁻¹. Yield-scaled N 2 O emissions (0.05 ± 0.01 kg N 2 O–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 N 2 O 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. Image 1 • Global greenhouse vegetables contribute 0.067 Tg N 2 O–N yr⁻¹ to atmospheric N 2 O. • N leaching from greenhouse vegetable production contributes 1.66 Tg N yr⁻¹ to groundwater pollution. • N 2 O emissions were higher, and N leaching lower if chemical + organic fertilizers were used. • Low N losses and high N use efficiency were detected at N fertilization rates <500 kg N ha⁻¹ yr⁻¹. • Yield-scaled N 2 O emission and N leaching was lower at N fertilization rates <1000 kg N ha⁻¹ yr⁻¹. [ABSTRACT FROM AUTHOR]