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在有防雨设施的试验田里，设置不同的土壤水分处理，应用１５Ｎ示踪技术研究土壤水分对氮素有效性的影响。试验结果表明：冬小麦对肥料氮素的利用率随土壤水分提高而提高；土壤供应的有效性氮素（Ａ值）在土壤水分由田间持水量的５０％ 提高到６０％ 时出现“跃迁”，土壤水分超过田间持水量的６０％ 以后，Ａ值差异不显著，表明土壤氮素有效性对土壤水分存在一个阈值反映。节水、节肥高效的土壤水分下限应控制在土壤田间持水量的６０％ 以上。
In the experimental field with rain-proof facilities, different soil moisture treatments were set up, and the effect of soil moisture on the effectiveness of nitrogen was studied by 15N tracing technique. The results showed that the nitrogen utilization efficiency of winter wheat increased with the increase of soil moisture. The available nitrogen (A value) of soil supplied a “transition” when soil moisture increased from 50% to 60% After the soil moisture exceeded 60% of the field capacity, the difference of A value was not significant, indicating that soil nitrogen availability had a threshold value of soil moisture. Water, fertilizer and efficient soil moisture limit should be controlled in the soil field water capacity of more than 60%.