水分亏缺程度对变量灌溉水分传感器埋设位置预判的影响

基于土壤黏粒含量遴选可代表平均土壤含水率的点位,是确定变量灌溉系统土壤水分传感器网络埋设位置的重要方法。为了评估水分亏缺程度对传感器埋设位置的影响,该研究通过在不同土壤可利用水量管理区内设置不同的水分亏缺灌溉处理,基于土壤含水率时间稳定性原理,分析了水分亏缺程度和土壤性质对冬小麦主要根系层内土壤含水率空间分布结构相似性和直接代表平均土壤含水率点位的影响。结果表明,受土壤性质和水分亏缺程度的影响,在土壤砂粒含量随土层深度增加而增大的1区,土壤含水率空间分布结构相似性仅在2016年的雨养处理达到了显著水平(P0.05),而在土壤剖面质地均匀的2区,2016年的雨养和高、中、低水分亏缺处理和2017年的中、低水分亏缺处理均达到了显著水平(P0.05)。在冬小麦主要根系层内,不同土壤性质管理区直接代表平均土壤含水率点位占总测点数的比例基本相等。受水分亏缺程度的影响,1区直接代表平均土壤含水率的测点比例随水分亏缺程度减小而增加,2区则呈先减小后略有增加趋势。除2016年高水分亏缺处理外,0~0.2、0.2~0.4、0.4~0.6 m土层代表平均土壤含水率点位的黏粒含量与该土层平均黏粒含量之间均存在显著的线性关系(P0.05),2 a拟合系数变化范围为0.66~1.03,且2017年拟合系数随土壤水分亏缺程度增加呈增大趋势。因此,在砂壤土地块变量灌溉管理区内,基于管理区平均土壤黏粒含量进行土壤水分传感器埋设位置遴选时,需根据拟采用的水分亏缺管理模式对拟合系数进行修正。

Influence of water stress level on determination of soil moisture sensor position under variable rate irrigation

Abstract: Determining positions to represent mean soil water content based on soil clay contents is an alternative method for positioning soil water content sensors in wireless sensor networks for a variable rate irrigation system. The field was divided into 4 management zones according to available soil water holding capacity (AWC). Two of the 4 management zones were selected to arrange the rain-fed treatment and 3 irrigation treatments representing different water stress levels to assess the effect of the levels on the placement of soil water content sensors under variable rate irrigation system. In zone 1, sand fraction largely increased with depth with AWC within 1-m soil profile ranging from 152 to 161 mm. In zone 2, a relatively uniform profile was observed along the profile with AWC within 1-m soil profile ranging from 161 to 171 mm. Based on the temporal stability of soil water content, the effects of soil water status and soil properties on the similarity of soil water spatial pattern and the positions directly representing the plot-mean soil water content were studied. Results showed that both of soil texture and water stress had effect on the structure similarity of soil water content distribution. In zone 1, the average Spearman''s rank correlation coefficient of 0-0.6 m was significant at the probability level of 0.05 only in the rain-fed treatment in the 2016 season. In zone 2, the Spearman''s rank correlation coefficient was significant at the probability level of 0.05 in all treatments in the 2016 season and in the medium and low water stress treatments in the 2017 season. The percentages of positions directly representing the mean soil water content were almost the same in zones 1 and 2. Affected by soil water status, the percentages increased as the level of soil water stress decreased in zone 1. While in zone 2, as the severity of water stress decreased, the percentages decreased and then had a slight increase. In general, significant linear regressions (P<0.05) between the mean clay content and the clay content representing the mean soil water content sites were found in layers 0-0.2, 0.2-0.4, and 0.4-0.6 m for all the treatments in 2016 and 2017, except for that in the severe water stress treatment in 2016. The fitted equation coefficients ranged from 0.66 to 1.03 in the 2 seasons, demonstrating a clearly increasing trend as the severity of water stress increased in 2017. When the mean clay content was used for a priori identification for positioning soil water content sensors in the management zones under variable rate irrigation system in a field with sandy loam soil, the strategies of water stress management should be considered in determining a fitted equation coefficients.