Modling Study Of Nitrogen Losses Based On GIS In Yinnan Irrigation District

Excessive nitrogen is a major cause of surface water pollution, and the main source of nitrogen is from fertilizers used in agriculture. This study based on field drainage experiment, modleing and theoretical analysese, investigated nitrogen losses from rice fields in YinNan Irrigation District (YNID) with geographical information system (GIS) technology. The field hydrology model, DRAINMOD, was calibrated for simulating water movement, and nitrogen loss was estimated with simulated hydrological data and measured N concentration. Main results are as follows:1. Relating the unique hydrological and climatic situations in YNID, DRINMOD was calibrated, and further used to simulate drainage flow under various system layout;2. The simulated results show that, for the growing seaons of 2004, the drainage volume from rice field was 58.3 cm on average, accounting for 44.8% total irrigation. For fields with narrower spacing, drainage volume could reach 96.2cm, or more than 60% of irrigation depth. This verified the varying extends of "large irrigation, large drainage" in the studying area;3. Nitrogen loss calculated from simulated results and measured N concentration indicated that, the loss in May and June was the highest, often 2-3 times higher than in July and August. The total nitrogen loss was 336.8 kg in the whole season, or 9.68 kgN/hm~2, accounting for 3.9% of the total fertilization application.4. Simulations show that controlled draining could reduce subsurface drainage by 46.8%, and nitrogen loss by 52.7% in.5. A lumped parameter water quality model indicated that the decay of nitrogen in lateral and main drainage path was rather weak;6. The nitrogen transfer process in ditch was integrated into a GIS using Mapinfo as platform; the GIS system also served as a user-friedndly data management tool for the YNID.