Optimum nitrogen use and reduced nitrogen loss for production of rice and wheat in the Yangtse Delta region.
A long-term field and lysimeter experiment under different amount of fertilizer-N application was conducted to explore the optimal N application rates for a high productive rice-wheat system and less N leaching loss in the Yangtse Delta region. In this region excessive applications of N fertilizer for the rice-wheat production has resulted in reduced N recovery rates and environment pollution. Initial results of the field experiments showed that the optimal N application rate increased with the yield. On the two major paddy soils (Hydromorphic paddy soil and Gleyed paddy soil) of the region, the optimal N application rate was 225-270 kg N hm(-2) for rice and 180-225 kg N hm(-2) for wheat, separately. This has resulted in the highest number of effective ears and Spikelets per unit area, and hence high yield. Nitrogen leaching in the form of NO(3-)-N occurs mainly in the wheat-growing season and in the ponding and seedling periods of the paddy field. Its concentration in the leachate increased with the N application rate in the lysimeter experiment. When the application rate reached 225 kg N hm(-2), the concentration rose to 5.4-21.3 mgN l(-1) in the leachate during the wheat-growing season. About 60% of the leachate samples determined contained NO(3-)-N beyond the criterion (NO(3-)-N 10 mg l(-1)) for N pollution. In the field experiment, when the N application rate was in the range of 270-315 kg hm(-2), the NO(3-)-N concentration in the leachate during the wheat-growing season ranged from 1.9 to 11.0 mg l(-1). About 20% of the leachate samples reached close to, and 10% exceeded, the criterion for N pollution. Long-term accumulation of NO(3-)-N from leaching will no doubt constitute a potential risk of N contamination of the groundwater in the Yangtse Delta Region.
Wang
D J
DJ
Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. djwang@issas.ac.cn
Liu
Q
Q
Lin
J H
JH
Sun
R J
RJ
D000383:Agriculture; D002681:China; D004784:Environmental Monitoring; D005308:Fertilizers; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism*; D012275:Oryza; D012621:Seasons; D012987:Soil; D014908:Triticum; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis / Q000378:metabolism*; D014881:Water Supply
D005308:Fertilizers; D012987:Soil; D014873:Water Pollutants; D009584:Nitrogen