Effects of Application of Nitrogen on Vegetable Yield, Nitrogen Balance and Soil Nitrogen Accumulation Under Two Years’ Drip Fertigation

【Objective】 Effects of conventional application of N and reduced application of N on vegetable yield and nitrogen balance and nitrogen accumulation and nitrate leaching under two years’ drip fertigation in irrigation areas by diverting water from Yellow Rriver of Ningxia were studied. 【Method】The experiments under greenhouse conditions were conducted with tomato-tomato-cucumber-tomato planting system from 2004 to 2006.【Result】The first two season’s tomato yield and total assimilated N were not increased in the conventional application of nitrogen and increased/decreased application of nitrogen treatment. After two seasons, with the decrease of application of nitrogen, the tomato’s yield in fourth season decreased by 48.7-72.3t·ha-1 compared with the yield in the first season, with the increasing application of nitrogen, the vegetable yield and total assimilated N were increased. Over application of nitrogen caused high accumulation of NO3--N within upper soil(0-30 cm) after first season tomato harvest, the NO3--N accumulation within upper soil after the fourth season harvest were reduced by 91.1%-92.2% compared with after first season harvest. Different application of nitrogen at different rates caused soil NO3--N accumulation moving down. NO3--N accumulation within 60-90 cm soil after the second tomato harvest increased by105.4%-137.3% compared with that after the first tomato harvested. Compared with that after the first tomato harvest, the NO3--N accumulation within 60-90 cm soil increased by 4.8%-30.8% after the third cucumber harvest, but the soil NO3--N accumulation under soil depth 120 cm changed a little. It was possible that the organic fertilizer moved down after four seasons of vegetable planting. Under the treatment of organic fertilizer, compared with that after second tomato harvest, the NO3--N accumulation within 60-90 cm soil increased by 22.7% after the fourth tomato harvested. Under the planting system of cucumber-tomato, dripping amount and the content of upper soil (0-30 cm) water made a significant difference to NO3--N in soil solution. The NO3--N of soil solution in upper layer (0-30 cm) could leach down, especially in the application of nitrogen treatment. The application of nitrogen and irrigation took the main place in nitrogen input, the soil Nmin residue took the main place in nitrogen output.【Conclusion】 Under the condition of drip fertigation in vegetable planting in greenhouse, season’s vegetable yield in conventional application of N (800 kg·ha-1) were not increased and caused high accumulation of NO3--N in upper soil layer (0-30 cm) after first season vegetable harvest and caused soil NO3--N accumulation moving down after next vegetable harvest, it is feasible to reduce nitrogen application. Based on organic fertilizer and phosphor (P) nitrogen fertilizer and potassium (K) fertilizer, the nitrogen fertilizer application was about 100-150 kg·ha-1 for autumn-winter season tomato, about 250-300 kg·ha-1 for winter-spring season tomato, about 400-450 kg·ha-1 for autumn-winter season cucumber.