Field Measurement Of Nitric Oxide Fluxes From A Water-Saving Ground Cover Rice Production System In China

Due to the increasing of the demand for food and the declining of irrigation water supply, security problems of food are facing unprecedented challenges in Asia. To safeguard food security and preserve precious water resources, the technology of water-saving ground cover rice production system (GCRPS) are being increasingly adopted in the agricultural production sector of rice production. However, compared to the conventional paddy pattern with intermittent irrigation water regime, changes in soil environment under GCRPS will affect soil biogeochemical processes that regulate nitric oxide (NO) flux, an important environmental pollution gas. To dater, the research on NO emissions of rice fields were mainly concentrated in the conventional paddy pattern, but the effect on NO emissions of water-saving ground cover rice production system were few. Therefore, in order to quantify the difference in NO fluxes between GCRPS and conventional paddy and to identify their controlling factors, the NO fluxes were in situ anniversary measured and comparative analysis of observational data from a rice-fallow rotation cropping system under different fertilizer treatments (conventional fertilization and no N fertilization as a control) of two production patterns, based on a method of static opaque chamber and chemiluminescent analysis.The research setted up two moisture management patterns:conventional paddy pattern and water-saving ground cover rice production system. The two planting conditions setted up no nitrogen treatment (conventional paddy pattern and GCRPS were C-NN and G-NN, respectively) and N-fertilized (conventional paddy pattern and GCRPS were C-UN and G-UN, respectively) treatment. According to the local farmers, a total of 150 kg N ha-1 urea was used in the N-fertilized treatment (90 kg N ha-1 for basal application applied, 30 kg N ha-1 for dressing during mid-tillering stage,30 kg N ha-1 for dressing during panicle initiation stage).The results are as follows:(1) During the rice-growing season, the high NO emissions of rice-growing season were mainly observed during the mid-season drainage period. In the fallow season, the NO fluxes in each treatment have the same seasonal dynamics which is negatively correlated with soil water content.(2) In the rice-growing season, the average seasonal emission fluxes of NO under conventional paddy was 2.00±0.88μg N m-2 h-1 and the total amount of seasonal emission was 0.06±0.01 kg N ha-1. The average seasonal emission fluxes of NO under GCRPS was 5.24±2.23μg N m-2 h-1 and the total amount of seasonal emission was 0.16±0.04 kg N ha-1 Whether average emission fluxes of NO or the total amount of seasonal emission, NO emission under GCRPS was greater than that of conventional paddy. In the fallow season, the NO fluxes in each treatment were 0.17-0.30 kg N ha-1, and there were no significant differences in NO emissions between GCRPS and conventional paddy. During the whole period, conventional paddy and GCRPS have the same total amount of annual emission, which were 0.35 å'Œ 0.36 kg N ha-1 yr-1, respectively.(3) The seasonal NO direct emission factors and annual emissions factors of conventional paddy were 0.016% and 0.032%. The seasonal NO direct emission factors and annual emissions factors of GCRPS were 0.12% and 0.15%. The GCRPS had potential trend to icrease NO emissions than conventional paddy.(4)Under the N-fertilized treatment, the water-saving ground cover rice production system could increase the grain yield by 3% comparing with conventional paddy pattern, and the grain yield of GCRPS was 8.1t ha-1.Based on the whole period, conventional paddy and GCRPS do not have the same NO annual dynamic, completely. In the rice-growing season, the fluxes of NO under conventional paddy was low, and the high NO emissions under GCRPS were mainly observed during the mid-season drainage period. In the fallow season, the two pattern of NO emissions present "spring emissions, less emissions in autumn and winter", which is negatively correlated with soil water content. Compared to conventional paddy, the N-fertilized treatment under GCRPS increased the NO emissions in the rice-growing season, but across the annual rotation cycle, the GCRPS have no significant increase in NO emissions, relatived to the conventional paddy.