Effect Of Management Practices On N₂O Emission And Denitrification Product Ratio In Greenhouse Vegetable Fields

For typical greenhouse vegetable cropping system in China, relateivly high fertilizer and water inputs will significantly affect soil nitrogen denitrification process, resulting in nutrient losses, greenhouse gas emissions and other environmental issues. In this paper, we selected typical solar greenhouse in Fangshan, Beijing and Shouguang, Shandong to measure the N2O emission flux under different water, carbon and nitrogen managements by statics-chamber method. The dynamic changes of environmental factors such as soil temperature, moisture and inorganic nitrogen content were also monitored to judge the key driving factors of N2O emissions. The Robot automatic incubation system was used to monitor the dynamic changes of soil gaseous products such as CO2, NO, N2O and N2, to find if temperature or different water, carbon and nitrogen management practices have any effects on nitrogen denitrification and product ratio, and to estimate denitrification loss at the field scale. According to the data from field measurements and published literature, we used models to simulate the N2O background emissions and emission factors, and to estimate N2O emissions from greenhouse vegetable fields of major provinces and cities in north China plain. The aim of this study is to provide datasets for theoretical basis of developing low carbon agricultural managements, which can reduce N2O emissions and nitrogen losses from the greenhouse vegetable fields, and to make data supports to improve the greenhouse gas emissions inventory in China. The main results and conclusions are as follows:(1) N2O emissions from greenhouse vegetable fields are mainly drived by organic materials, irrigation rate and fertilizer inputs and so on. There were obvious seasonal variations in N2O emissions. The cumulative N2O emissions for conventional treatment, water and nitrogen recommended treatment and recommended combined with catch crop treatment were 9.5 kg N ha-1 yr-1,3.3 kg N ha-1 yr-1 and 3.6 kg N ha-1 yr-1 from greenhouse vegetable fields in Fangshan, Beijing respectively, which accounted for 1.1%,0.8%,0.9% of the chemical nitrogen fertilizer inputs and 0.6%,0.4%,0.6% of the total nitrogen fertilizer inputs. Compared with conventional nutrient resources management, the recommended treatments mitigated 61-66% of annual cumulative N2O emissions, conserved 52% of chemical fertilizer and 48% of irrigation water inputs without any yield reduction. N2O emission fluxes were significantly and positively correlated with surface soil moisture (WFPS), indicates that denitrification could be the major process for N2O emission.(2) The long-term water, carbon and nitrogen managements in the field had no significant effects on denitrification process and its product ratio. The temperature change and carbon and nitrogen substrates addition could have significant effects on denitrification rates, because soil respiration rate, N2O emission and denitrification rate were significantly higher at 20℃ than that at 15℃ in the anaerobic incubation. The most important limiting factor for N2O emissions was the carbon source, rather than inorganic nitrogen content in the soil. The N2O/(NO+N20+N2) denitrification product ratio in soil from the vegetable field in Fangshan, Beijing and soil in Shouguang, Shandong were 0.39-0.45 and 0.54-0.71, respectively. The gaseous losses through denitrification were 7.7-21.1 kg N ha-1 yr-1 and 27.3-43.7 kg N ha-1 yr-1 from the Fangshan, Beijing field and Shouguang, Shandong field respectively, which accounting 1.9-2.4% and 2.2-2.8% of chemical nitrogen fertilizer inputs.(3) Nitrogen inputs and background emission significantly contribute to N2O emissions from greenhouse vegetable fields. The least squares (OLS) linear regression model and maximum likelihood estimation model were used forthe estimation. Using the above two models, the estimated chemical fertilizer N2O emission factors were 0.78% and 0.49%, and the N2O background emissions were 1.53 kg N ha-1 yr-1 and 0.50 kg N ha-1 yr-1 from typical greenhouse vegetable fields in north China plain, respectively. According to the estimation of OLS model, direct N2O emissions in 2013 were 0.31 Gg N, 0.69 Gg N,3.08 Gg N and 1.93 Gg N, the background emissions were 0.06 Gg N,0.10 Gg N,0.61 Gg N and 0.23 Gg N from greenhouse vegetable fields in Beijing, Tianjin, Hebei and Shandong, respectively.