Soil N2O emission characteristics of greenhouse tomato fields under aerated irrigation

Abstract: Global warming and ozone depletion caused by greenhouse gas emissions are two major global environmental issues. The contribution of facility vegetable fields abundant with high N input to soil nitrous oxide emissions cannot be negligible. Crop growth, yield and water use efficiency under aerated irrigation have been done much work, while the effects of aerated irrigation on greenhouse gas emissions have never been reported. Changes of oxygen content in the soil caused by the aerated irrigation are bound to affect the production and emissions of nitrous oxide. Field experiments by using the method of static chamber/gas chromatography were conducted to determine the effects of aerated irrigation on seasonal N2O fluxes, and cumulative emissions of N2O from soils in greenhouse tomato fields in autumn-winter season and soil water-filled pore space (WFPS) at 20 cm depth in the solar greenhouse of the Key Laboratory of Agricultural Soil and Water Engineering in Arid Area sponsored by Ministry of Education (34°20′N, 108°04′E), at Northwest A&F University, in Yangling, Shaanxi Province of China, from August 13, 2014 to December 28, 2014. Two factors (irrigation and aeration) were designed in the experiment to reveal the effects of aerated irrigation on soil N2O emissions. Four treatments with three replications (each plot size 4.0 m × 0.8 m) were contained in the experiment: aerated deficit irrigation (A1), unaerated deficit irrigation (CK1), aerated full irrigation (A2) and unaerated full irrigation (CK2). The results showed that N2O fluxes under different irrigation methods roughly showed a trend of decrease after the first increase. The first and secondary peaks of N2O fluxes were observed at fruit expanding stage and maturing stage of tomato, respectively, while kept at a low level in other periods. Both seasonal N2O fluxes and cumulative emissions of N2O at different growth stage of tomato followed the same pattern: A2>CK2>A1>CK1. And both N2O fluxes and cumulative emissions of N2O from soils in tomato fields at different growth stages for each treatment mainly concentrated at fruit expanding stage. In addition, aeration and full water supply treatments increased the soil N2O emissions during the whole tomato growth period compared to unaeration and deficit water supply treatments. The average value of N2O fluxes (38.00 μg/(m2·h)) for A2 treatment increased by 85.9% and 264.7% compared with that for A1 and CK1 treatment (P<0.05), respectively, while the difference was not significant when compared to CK2 treatment (P>0.05). The maximum value about cumulative emission of N2O (120.34 mg/m2) for A2 treatment was 1.89 and 4.21 times as much as A1 and CK1 (P<0.01), respectively, while the difference was not significant when compared to CK2 treatment (P=0.078). Compared with unaerated irrigation, aerated irrigation did not increase N2O emissions from soils in greenhouse tomato fields significantly under full water supply condition (P=0.078), while increased N2O emissions significantly under deficit water supply condition (P<0.01). In addition, WFPS kept at a relatively high level for each treatment during the whole tomato growth stage. Except the main peaks, N2O fluxes increased with WFPS increasing. Exponential positive correlations between N2O fluxes and soil water-filled pore space (WFPS) were observed under unaerated irrigation methods of different irrigation level (P<0.05), while the relationships under aerated irrigation methods were not significant (P>0.05). Furthermore, peaks of N2O emissions were negative with WFPS, and N2O intense release was observed when WFPS was between 46.0%-52.1%. The results suggested that aerated irrigation increased soil N2O emissions in tomato fields, and the difference was significant under deficit water supply condition. This study provides valuble information for assessing farmland ecological effects of aerated irrigation and mitigating greenhouse gas emissions to greenhouse soils.