壤土特性空间变异对地下滴灌水氮分布及夏玉米生长的影响

Water and Nitrogen Distribution and Summer Maize Growth in Subsurface Drip Irrigation System as Affected by Spatial Variations of Soil Properties

【目的】与地表滴灌相比,地下滴灌的特殊性在于系统性能不仅受水力设计参数的影响,而且还与土壤特性的空间变异密切相关。本文的目的是定量评估地下滴灌系统水力参数和土壤特性空间变异对土壤水氮空间分布和夏玉米生长的影响。【方法】试验田块的土壤为砂质壤土。试验中滴灌带埋深设置0、15和30cm3个水平,施肥装置选择国内外常用的压差式施肥罐和文丘里施肥器两种类型;土壤特性测试指标包括颗粒组成、容重、水分特征曲线、含水量、硝态氮和铵态氮含量。采用人工神经网络模型估算了土壤饱和导水率。夏玉米收获时测定了地上部分干物质、产量和氮素吸收量的分布。【结果】试验田块内土壤初始硝态氮含量的变异程度最大,饱和导水率次之,土壤容重的变异程度最小;土壤特性空间变异程度为弱-中等。滴灌带埋深对施肥灌溉后土壤硝态氮在垂直剖面上的分布影响明显,滴灌带附近一般硝态氮含量较高。但施肥装置类型对土壤硝态氮分布的影响不显著;滴灌带埋深和施肥装置类型对土壤铵态氮含量分布的影响均不显著。由地下滴灌系统水力设计和土壤特性空间变异引起的作物地上部分干物质、吸氮量和产量的变异系数明显小于灌溉施肥后土壤氮素的变异系数,接近或小于灌水量与施肥量的变异系数。【结论】对试验土壤来说,土壤特性的空间变异,尤其是土壤初始含水量和氮素含量的不均匀性,可能是导致施肥灌溉后土壤水氮分布不均匀的重要原因。因此在地下滴灌系统设计中应考虑土壤特性空间变异的影响。

【Objective】In contrast to surface drip irrigation,both hydraulic design and spatial variations of soil properties can impose influence on the system performance of subsurface drip irrigation （SDI）. Field experiments were conducted on a sandy loam soil to investigate the effects of hydraulic design of SDI system and spatial variations of soil properties on water and nitrogen distribution and summer maize growth. 【Method】In the experiments,dripline depths were varied from 0 to 30 cm and two injector types,a differential pressure tank and a Venturi device,were used. Spatial variations of soil properties,including soil particle size distribution,bulk density,soil water characteristic curve,soil water content,and nitrate and ammonium nitrogen contents were tested. Saturated hydraulic conductivity was determined by an artificial neural network model from particle size distribution and bulk density. On harvest of summer maize,total dry matter above ground,yield,and nitrogen uptake were measured. 【Result】 The results indicated that initial nitrate content had the largest variability with a coefficient of variation CV ranging from 0.51 to 1.58,saturated hydraulic conductivity had a moderate CV of 0.31-0.44,and soil bulk density had a smallest CV of ≤0.06. Dripline depth had a significant effect on the vertical distribution of nitrate following a fertigation event. A greater nitrate content generally occurred at the proximity of the dripline buried positions,while injector types had an insignificant influence on nitrate distribution. No significant effect on ammonium distribution of dripline depths and injector types was found. The variability of total dry matter above ground,nitrogen uptake,and yield caused by hydraulic design and soil properties variation was least with CV considerably smaller than soil nitrogen contents but approximate water and fertilizer applied CV. 【Conclusion】Our experiments demonstrated that the nonuniform distribution of water and nitrogen in the soil following a fertigation event was mainly caused by the spatial variation of soil properties,especially the initial distribution of soil water and nitrogen contents. It is suggested that the spatial variations of soil properties should be considered in the design of SDI systems.