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Field Characterization of Field Capacity and Root Zone Available Water Capacity for Variable Rate Irrigation

机译:变量灌溉田间容量和根区有效水容量的田间特征

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摘要

Accurate spatial characterization of field capacity (FC) and root zone available water capacity (R) can enhance site-specific management practices—such as variable rate irrigation—to lower input costs, reduce contaminant leaching, and/or improve crop yield. Measuring the volumetric water content after wet soils drain following substantial precipitation can provide a field estimate of FC. The average FC (FCa) for the managed root zone was determined at thirty-two locations in a topographically variable field in south central Nebraska. The difference between FC and permanent wilting point estimates—computed using a pedotransfer function—yielded values for R for the observation locations. Sampling locations were too sparse for reliable interpolation across the field. Therefore, relationships between a surrogate, or predictor, variable and soil water properties were used to provide spatial distributions of FC and R for the field. Field estimates of FCa and R were more strongly correlated to elevation (correlation coefficient, r = -0.77 and - 0.76, respectively) than to deep soil apparent electrical conductivity (r = -0.46 and -0.39, respectively). Comparing maps of FCa and R from gSSURGO to maps from field characterization yielded a root mean squared difference of 0.031 m3 m-3 for FCa and 34 mm for R. Sampling seven locations across the elevation range in this field produced FCa and R prediction functions that achieved 95% and 87%, respectively, of the reduction in the standard error achievable with a larger number of sampling locations. Spatial characterization of FCa and R depends on identifying a suitable predictor variable(s) based on field knowledge and available spatial data. Well-chosen variables may allow satisfactory predictions using several sampling locations that are distributed over the entire field. Ultimately, the costs and benefits of spatial characterization should be considered when evaluating site-specific water management.
机译:田间容量(FC)和根区可用水容量(R)的准确空间特征可以增强特定地点的管理实践(例如可变速率灌溉),以降低投入成本,减少污染物淋失和/或提高作物产量。在大量降水后测量湿土壤流失后的体积水含量可以提供FC的现场估算值。在内布拉斯加州中南部的地形变化领域中,在32个位置确定了管理根区的平均FC(FCa)。 FC和永久性枯萎点估计之间的差异(使用pedotransfer函数进行计算)得出了观测位置的R值。采样位置太稀疏,无法在整个现场进行可靠的插值。因此,使用替代变量或预测变量与土壤水分属性之间的关系来提供田间FC和R的空间分布。 FCa和R的现场估计值与海拔高度(相关系数分别为r = -0.77和-0.76)相关,而与深层土壤表观电导率(分别为r = -0.46和-0.39)具有更强的相关性。比较来自gSSURGO的FCa和R的图与来自现场表征的图,得出FCa的均方根差为0.031 m3 m-3,R的均方根差为34 mm。在该场高程范围内的七个位置采样产生了FCa和R预测函数大量采样位置可实现的标准误降低分别达到95%和87%。 FCa和R的空间表征取决于根据领域知识和可用空间数据确定合适的预测变量。选择好的变量可以使用分布在整个字段中的几个采样位置进行令人满意的预测。最终,在评估特定地点的水资源管理时应考虑空间表征的成本和收益。

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