渭北旱塬苹果园土壤深层干燥化与硝酸盐累积

以渭北旱塬的苹果园为研究对象，对5～34龄苹果园土壤剖面水分含量分布与硝酸盐累积状况进行研究．结果发现，旱地苹果园的高投入与高产出经营方式不但导致了土壤深层干燥化，而且土壤深层累积了大量的硝态氮，累积层在40～260cm土层，最高含量达403．4mg·kg^-1．由于连续施氮肥，这些氮素被再利用的可能性很小，存在土体中的硝态氮会造成潜在的环境问题．由于土壤深层水对干旱的调节作用减弱或丧失，导致苹果产量受控于当季节降水．因此，应当控制苹果园施氮量，避免氮素的大量累积，并采取措施改善果园水分状况。

Desiccation and nitrate accumulation of apple orchard soil on the Weibei dryland

The study of apple orchard soil on the Weibei dryland showed that high input and high yield not only resulted in soil desiccation, but also induced nitrate accumulation in the soil profile. Generally, the soil layers with accumulated nitrate located in 40 - 260 cm depths, and the maximum nitrate content was 403.4 mg x kg(-1). Owing to the continuous application of nitrogen fertilizer, the accumulated nitrate could hardly be reused in the future, which might lead to environmental pollution. Because the soil storage water could not adjust the water utilization of apple trees, the yield of orchard was affected by precipitation. Therefore, the nitrogen application rate should be reduced, and actions should be taken to improve soil moisture in apple orchard.