Effect of rice intermittent irrigation on nitrogen cycle and emission in a lysimeter study

Abstract

Although intermittent irrigation is widely regarded as a saving irrigation water technology in paddy fields, it can cause water and air pollution by changing the nitrogen cycle. A two-year lysimeter experiment was conducted to investigate the effect of intermittent irrigation on the nitrogen cycle. For applying intermittent irrigation, soil drying began about 30 days after transplanting and the alternate wetting and drying was considered weekly. To investigate the nitrogen cycle in the lysimeter, nitrate and ammonium concentrations and acidity were measured periodically at depths of 18, 30, and 70 cm. Results showed that water saving was 23-24%, which varied over two years depending on the weather conditions. The most nitrate and ammonium concentration changes occurred at a depth of 30 cm in 2018 and a depth of 70 cm in 2019. Nitrate concentration after two dried periods at a depth of 30 cm indicated the producing and leaching of nitrate in the soil, which upraised the risk of groundwater contamination. Nitrate concentration in the dried period increased compared to the previously flooded period, although the rate of increase was variable in each alternation. The reduction of ammonium concentration was about 13% in the first alternation at a depth of 30 cm, which was much lower in the following periods. Nitrogen balance in the surface layer showed that 39 and 51% ammonium volatilization and rice uptake occurred, respectively. Denitrification was obtained 0.5 kg N ha-1 which could be as an index for the emission of N2O. Total nitrogen loss based on applied nitrogen fertilizer was 52%, of which 47% is caused by ammonium volatilization. Results showed the importance of the number of alternations in nitrogen changes in paddy fields.

Keywords

• ammonium
• denitrification
• rice uptake
• volatilization