Atefeh M. Soltani - Water Engineering Department, Agricultural Sciences Faculty, University of Guilan
Maryam Navabian - Water Engineering Department, Agricultural Sciences Faculty, University of Guilan & Department of Water Engineering and Environment, University of Guilan. Rasht, Iran

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 ۳۰ 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 ۱۸, ۳۰, and ۷۰ cm. Results showed that water saving was ۲۳-۲۴%, which varied over two years depending on the weather conditions. The most nitrate and ammonium concentration changes occurred at a depth of ۳۰ cm in ۲۰۱۸ and a depth of ۷۰ cm in ۲۰۱۹. Nitrate concentration after two dried periods at a depth of ۳۰ 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 ۱۳% in the first alternation at a depth of ۳۰ cm, which was much lower in the following periods. Nitrogen balance in the surface layer showed that ۳۹ and ۵۱% ammonium volatilization and rice uptake occurred, respectively. Denitrification was obtained ۰.۵ kg N ha-۱ which could be as an index for the emission of N۲O. Total nitrogen loss based on applied nitrogen fertilizer was ۵۲%, of which ۴۷% is caused by ammonium volatilization. Results showed the importance of the number of alternations in nitrogen changes in paddy fields.

Ammonium, Denitrification, Rice uptake, Volatilization