Nitric oxides and nitrous oxide fluxes from typical vegetables cropland in China: Effects of canopy, soil properties and field management

In China, vegetable croplands are characterized by intensive fertilization and cultivation, which produce significant nitrogenous gases to the atmosphere. In this study, nitric oxides (NOX) and nitrous oxide (N2O) emissions from the croplands cultivated with three typical vegetables had been measured in Yangtze River Delta of China from September 2 to December 16, 2006. The NO fluxes varied in the ranges of 1.6–182.4, 1.4–2901 and 0.5–487 ng Nm−2 s−1 with averages of 33.8 ± 44.2, 360 ± 590 and 76 ± 112 (mean ± SD) ngNm−2 s−1 for cabbage, garlic, and radish fields (n = 88), respectively. N2O fluxes from the three vegetable fields were found to occur in pulses and significantly promoted by tillage with average values of 5.8, 8.8, and 4.3 ng Nm−2 h−1 for cabbage, garlic, and radish crops, respectively. Influence of vegetables canopy on the NO emission was investigated and quantified. It was found that on cloudy days the canopy can only shield NO emission from croplands soil while on sunny days it cannot only prevent NO emission but also assimilate NO through the open leaves stomas. Multiple linear regression analysis indicated that soil temperature was the most important factor in controlling NO emission, followed by fertilizer amount and gravimetric soil water content. About 1.2%, 11.56% and 2.56% of applied fertilizers N were emitted as NO–N and N2O–N from the cabbage, garlic and radish plots, respectively.