关中地区小麦/玉米轮作农田硝态氮淋溶特点

通过田间原位淋溶装置研究了不同施氮量和秸秆覆盖对关中地区小麦/玉米轮作农田90cm深处硝态氮(NO3--N)淋溶量、0～1m土层硝态氮累积及作物产量和氮平衡的影响.试验设不施氮(N1,0kg·hm-2·a-1)、常规施氮(N2,471kg·hm-2·a-1)、推荐施氮(N3,330kg·hm-2·a-1)、减量施氮(N4,165kg·hm-2·a-1)、增量施氮(N5,495kg·hm-2·a-1)和推荐施氮+秸秆覆盖(N3+S)6个不同施肥处理.结果表明:NO3--N淋溶量随施氮量的增加而增大,氮肥的过量施用及秸秆覆盖易造成NO3--N淋溶.N3+S处理90cm处年NO3--N流失量最大,为22.32kg·hm-2,施肥造成的氮流失量为16.44kg·hm-2,比相同施氮量不覆盖处理(N3)高158.9%.NO3--N主要累积在20～60cm土层,年施氮量330kg·hm-2(N3)时,秸秆覆盖与否不影响NO3--N的剖面分布.各施肥处理对作物产量没有显著影响,但减量施氮处理(N4)有减少作物产量的趋势.在本试验条件下,推荐施肥量(小麦施氮150kg·hm-2,玉米施氮180kg·hm-2)在保证作物产量的同时,可减少土壤NO3--N的淋溶和累积.

Nitrate leaching characteristics of wheat-corn rotation farmland in Guanzhong area of Shaanxi

By using in situ leaching device,a field experiment was conducted to study the effects of nitrogen fertilization rate and straw mulching on the nitrate leaching at 90 cm soil depth,nitrate accumulation in soil profile(0-100 cm),crop yield,and nitrogen balance of wheat-corn rotation farmland in Guanzhong area of Shaanxi.Six treatments were installed,I.e.,no fertilization(N1,0 kg·hm~(-2)·a~(-1)),conventional fertilization(N2,471 kg·hm~(-2)·a~(-1)),recommended fertilization(N3,330 kg·hm~(-2)·a~(-1)),reduced N application(N4,165 kg·hm~(-2)·a~(-1)),increased N application(N5,495 kg·hm~(-2)·a~(-1)),and recommended fertilization plus straw mulching(N3+S).The nitrate leaching loss was increased with increasing N fertilization rate.Excessive N fertilization and straw mulching could easily cause nitrate leaching.In treatment N3+S,the annual NO_3~--N loss at 90 cm soil depth was the greatest(22.32 kg N·hm~(-2)),and the NO_3~--N loss from N fertilization was 16.44 kg N·hm~(-2)·a~(-1),being 158.9% higher than that in treatment N3.Nitrate mainly accumulated in 20-60 cm soil layer.When the N application rate was 330 kg N·hm~(-2)·a~(-1),straw mulching had less effect on the NO_3~(-)-N distribution in soil profile.No significant difference was observed in the crop yield among the treatments,but reduced N application(N_4)tended to decrease the yield.Under our experimental condition,a fertilization rate of150 kg N·hm~(-2)·a~(-1) for wheat and 180 kg N·hm~(-2)·a~(-1) for maize could ensure the crop production and reduce the soil nitrate leaching and accumulation.