Temporal Stability of Spatially Measured Soil Matric Potential Probability Density Function

Abstract

Estimation of mean water status in a field is crucial to effective irrigation water management. Problems encountered with the estimation of mean field soil water status may be attributed to spatial variability of soil physical properties. Several investigators have shown temporal stability of spatial patterns of field measured soil water content, but temporal stability of field measured soil matric potential (ψm), a measure of soil water status more appropriate for irrigation scheduling, has not previously been reported to last for more than a few days within one irrigation cycle. This study investigated the temporal stability of spatial patterns of ψm both within and between sequential irrigation cycles. Sixty locations in a 1‐ha field were outfitted with a 1‐m neutron probe access tube and three tensiometers placed at 0.15‐, 0.3‐, and 0.5‐m depths. The observations obtained from 14 d of soil water content measurements and 46 d of ψm measurements within eight irrigation cycles were analyzed with Spearman's rank correlation coefficients and a relative differencing technique. The results showed temporally stable soil water content spatial patterns and also indicated temporally stable ψm spatial patterns if assumptions of full soil wetting at the beginning of the cycle and uniform evapotranspiration among locations were satisfied. Several locations in the field estimated the field mean ψm to within 10% within a given range of potentials, and a few estimated the field mean to within 20% across the entire range of potentials tested. Other locations estimated the lower and higher percentiles of ψm with similar accuracy.