Spatial variability of field-measured soil-water properties

Infiltration and redistribution of water following an irrigation was studied, and the work was replicated at 20 locations on a 150 hectare plot of land. Hydraulic conductivity was measured as a function of soil-water content at 30.5 cm depth intervals to a depth of 182.9 in twenty 6.5-meter-square plots randomly established over a 150-hectare field. Tensiometers installed at 30.5, 61.0, 91.4, 121.9, 152.4, and 182.9 cm were used to measure hydraulic gradients. Soil-water contents were ascertained from soil-water characteristics obtained from six soil cores taken from each of the above depths for each plot. Variations in soil-water content were found to be normally distributed with depth and with horizontal distance throughout the field, while values of the hydraulic conductivity were found to be log-normally distributed. The correlation between hydraulic conductivity during steady-state infiltration and the clay fraction was significant at the 1 per cent level. Several equations for predicting water movement and retention under field conditions are examined.