干旱区滴灌均匀系数对土壤水氮分布影响模拟

基于HYDRUS-2D软件建立了棉花膜下滴灌水氮运移模型,利用干旱区棉花膜下滴灌试验数据对模型进行了参数率定和验证。将灌水器流量沿毛管的变化离散为依次逐段减小,并假设土壤水分在各段之间不存在交换,利用验证后的数学模型研究了干旱区不同滴灌均匀系数时土壤水氮分布特征,评估了土壤空间变异对水氮分布均匀性的影响。模拟结果表明,随着灌水的进行,滴灌均匀系数Cu为0.60和0.80时,土壤含水率和NO-3-N质量浓度均匀系数均呈下降趋势,而Cu=0.95时变化较平稳;滴灌均匀系数越低,灌水后土壤含水率和NO-3-N质量浓度均匀系数降低的幅度越大;土壤NO-3-N质量浓度均匀系数的变化范围为0.35~1.00,低于土壤含水率均匀系数。田间试验存在的土壤空间变异在一定程度上增加了土壤水氮分布不均匀性。

Modeling Distributions of Water and Nitrate in Soil as Affected by Drip System Uniformity under Arid Conditions

A model simulating the transport of water and nitrate in soil under mulched drip irrigation of cotton was established and solved numerically by using the HYDRUS-2D package. The model was calibrated and validated by the field experiments conducted in Urumqi, Xinjiang Uygur Autonomous Region, China, during the cotton growing seasons of 2010 and 2011. The emitter discharge rates that progressively decreased from the inlet to the distal end along the dripline were discretized as a series of sequential segments each having an equal discharge rate. Assuming no lateral exchange of water in soil between adjacent segments, the model, which had been verified, was used to evaluate the effect of drip system uniformity and soil spatial variability on the distributions of water and nitrate in soil under arid conditions. The results indicated that the uniformity coefficients of soil water content and nitrate were observed in downward trend for drip system uniformity coefficients (Cu) of 0.60 and 0.80, while a relatively stable variation pattern was observed for Cu=0.95; the lower system uniformity the greater decrease in the uniformity coefficient of soil water content and nitrate following an irrigation event was observed. The uniformity coefficient of soil nitrate, which varied from 0.35 to 1.00, was substantially lower than that of soil water content. Meanwhile, the soil spatial variability in the experimental field increased the nonuniform distributions of the soil water and nitrate.