摘要
The rice-wheat rotation in southern China is characterized by frequent flooding-draining water regime and heavy nitrogen(N)fertilization. There is a substantial lack of studies into the behavior of dissolved organic nitrogen(DON) in the intensively managed agroecosystem. A 3-year in situ field experiment was conducted to determine DON leaching and its seasonal and yearly variations as affected by fertilization, irrigation and precipitation over 6 consecutive rice/wheat seasons. Under the conventional N practice(300kg N ha-1for rice and 200 kg N ha-1for wheat), the seasonal average DON concentrations in leachate(100 cm soil depth) for the three rice and wheat seasons were 0.6–1.1 and 0.1–2.3 mg N L-1, respectively. The cumulative DON leaching was estimated to be1.1–2.3 kg N ha-1for the rice seasons and 0.01–1.3 kg N ha-1for the wheat seasons, with an annual total of 1.1–3.6 kg N ha-1. In the rice seasons, N fertilizer had little effect(P > 0.05) on DON leaching; precipitation and irrigation imported 3.6–9.1 kg N ha-1of DON, which may thus conceal the fertilization effect on DON. In the wheat seasons, N fertilization had a positive effect(P < 0.01)on DON. Nevertheless, this promotive effect was strongly influenced by variable precipitation, which also carried 1.8–2.9 kg N ha-1of DON into fields. Despite a very small proportion to chemical N applied and large variations driven by water regime, DON leaching is necessarily involved in the integrated field N budget in the rice-wheat rotation due to its relatively greater amount compared to other natural ecosystems.
The rice-wheat rotation in southern China is characterized by frequent flooding-draining water regime and heavy nitrogen（N）fertilization. There is a substantial lack of studies into the behavior of dissolved organic nitrogen（DON） in the intensively managed agroecosystem. A 3-year in situ field experiment was conducted to determine DON leaching and its seasonal and yearly variations as affected by fertilization, irrigation and precipitation over 6 consecutive rice/wheat seasons. Under the conventional N practice（300kg N ha^-1for rice and 200 kg N ha^-1for wheat）, the seasonal average DON concentrations in leachate（100 cm soil depth） for the three rice and wheat seasons were 0.6–1.1 and 0.1–2.3 mg N L^-1, respectively. The cumulative DON leaching was estimated to be1.1–2.3 kg N ha^-1for the rice seasons and 0.01–1.3 kg N ha^-1for the wheat seasons, with an annual total of 1.1–3.6 kg N ha^-1. In the rice seasons, N fertilizer had little effect（P 〉 0.05） on DON leaching; precipitation and irrigation imported 3.6–9.1 kg N ha^-1of DON, which may thus conceal the fertilization effect on DON. In the wheat seasons, N fertilization had a positive effect（P 〈 0.01）on DON. Nevertheless, this promotive effect was strongly influenced by variable precipitation, which also carried 1.8–2.9 kg N ha^-1of DON into fields. Despite a very small proportion to chemical N applied and large variations driven by water regime, DON leaching is necessarily involved in the integrated field N budget in the rice-wheat rotation due to its relatively greater amount compared to other natural ecosystems.
基金
supported by the Jiangsu Provincial Natural Science Foundation of China(No.BK-2010612)
the Foundation of State Key Laboratory of Soil and Sustainable Agriculture,China(No.Y05-2010034)
the National Natural Science Foundation of China(No.41001147)
