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在陕西渭北旱塬进行了2a田间试验,研究不同栽培模式、施氮量和小麦种植密度对旱地硝态氮残留的影响。结果表明,种植小麦2a后0~200 cm土壤剖面中残留硝态氮58.6~283.9 kg/hm2,数量可观,短期内在渭北旱塬深厚的土壤中不会对地下水造成威胁,但夏季休闲期间容易下迁至作物无法吸收的土壤深度。与常规无覆盖模式相比,地膜覆盖和垄沟种植显著提高了作物对氮素的吸收,但同时也增加了土壤0~200 cm的硝态氮残留,这与地膜覆盖导致有机氮矿化增加有关;秸秆覆盖对作物氮素吸收和硝态氮残留均没有明显影响。施氮量低于120 kg/hm2时,各种栽培模式土壤剖面残留硝态氮的分布差异较小,只有地膜覆盖和垄沟种植处理在土壤表层有少量硝态氮累积;施氮量为240 kg/hm2时,无覆盖和秸秆覆盖土壤60~120 cm深度都有明显累积峰,地膜覆盖和垄沟种植土壤残留硝态氮则在60 cm以上土层累积较多。小麦种植密度也影响了各种栽培模式土壤硝态氮及其分布特点。垄沟种植条件下,从土壤表层到200 cm的深层,垄上土壤残留硝态氮均显著高于沟内土壤;上层差异最大,随着土壤深度的增加其差异逐渐降低;随着施氮量的增加,这种差异显著增大;随小麦种植密度的增加则显著降低。随着施氮量增加,小麦吸氮量和土壤中残留硝态氮量均显著提高;施氮增加的残留硝态氮占施氮量的0.3%~44.6%。垄沟种植模式施氮增加的残留硝态氮最多,地膜覆盖处理次之,垄沟种植处理垄上土壤增加量远远高于沟内土壤。施氮量提高1倍,增加的残留硝态氮量平均提高了3倍多。提高小麦种植密度,施氮增加的残留硝态氮平均减小13.2 kg/hm2。由于种植密度增加显著提高了小麦对氮素的吸收,因此硝态氮残留有降低的趋势。其中,秸秆覆盖模式80~140 cm土层降低显著;地膜覆盖条件下高密与低密残留硝态氮的差异主要在深层;垄沟模式中,低密度种植硝态氮残留量在整个土壤剖面都高于高密度处理;而无覆盖条件下,残留硝态氮则随种植密度的提高呈增加趋势。
Field experiments were conducted in Weibei arid highland in Shaanxi Province to study the effects of different cultivation modes, nitrogen application rates and wheat planting density on nitrate residual in dryland. The results showed that the residual nitrate nitrogen in 0-200 cm soil profile after planting wheat 2a was 58.6 ~ 283.9 kg / hm2, which was significant in a short period. It would not be a threat to groundwater in the deep soil of Weibei dry land in a short term, Move down to the soil that the crop can not absorb. Compared with the conventional uncovered pattern, plastic film mulch and furrow drench significantly increased the N uptake by crops, but also increased nitrate residuals from 0 to 200 cm in the soil, which was related to the increase of organic nitrogen mineralization caused by plastic film mulching ; Straw mulching had no significant effect on crop nitrogen uptake and residual nitrate nitrogen. When the nitrogen application rate was less than 120 kg / hm2, there was little difference in the distribution of residual nitrate-N in the soil profiles of all cultivation modes. Only a small amount of nitrate accumulation was observed on the soil surface under mulching and furrow irrigation. / hm2, there was obvious accumulation peak in the depth of 60-120 cm without covering and straw mulching, while residual nitrate-N in the mulching and furrow planting soil accumulated more in the soil above 60 cm. Wheat planting density also affected soil nitrate nitrogen in various cultivation patterns and its distribution characteristics. Under the condition of furrow planting, the residual nitrate nitrogen in the ridge soil was significantly higher than that in the furrow from the soil surface to the depth of 200 cm. The difference in the upper layer was the largest, and the difference was gradually decreased with the increase of soil depth. With the increase of nitrogen application rate Increase, this difference significantly increased; with the increase of wheat planting density was significantly reduced. With the increase of N application rate, the nitrogen uptake by wheat and the residual nitrate content in soil increased significantly. The residual nitrate content increased by 0.3% ~ 44.6% of the N application rate. In the furrow ditch planting pattern, the amount of residual nitrate nitrogen increased with the increase of nitrogen application, followed by mulching with plastic film, and the increase of soil with ridge furrow planting was much higher than that with ditch soil. The amount of nitrogen application increased by 1 time and the amount of residual nitrate nitrogen increased by more than 3 times on average. Increasing the planting density of wheat increased the residual nitrate nitrogen by 13.2 kg / hm2 on average. As the planting density increased significantly nitrogen uptake by the wheat, the nitrate residual decreased. Among them, the straw mulching pattern decreased significantly in 80-140 cm soil layer. The difference of nitrate nitrogen in high-density and low-density mulching was mainly in the deep layer under mulching conditions. In the furrow pattern, the residual nitrate nitrogen in low density planting was high in the whole soil profile In high-density treatment, while no-cover conditions, the residual nitrate nitrogen increased with the planting density increased.