Hydraulic and thermal properties of a sandy soil as influenced by incorporation of sewage sludge

Soil-water retention was increased by incorporation of sewage sludge into a sandy soil. Most of this increase resulted from water adsorbed by organic matter (15-bar water). At any given water content, unsaturated hydraulic conductivity and soil-water diffusivity decreased as rates of sludge addition increased. However, saturated hydraulic conductivity increased as rates of sludge addition increased. Thermal conductivity decreased with increasing rates of sludge application. However, the heat capacity of all oven-dried sludge-soil mixtures was the same as that of the control treatment. The combination of a lower thermal conductivity and a higher specific heat (due to higher water content) buffered sludge-amended soil against sudden temperature changes. Thus, maximum and minimum daily temperatures on plots receiving sludge were a few degrees lower and higher, respectively, than those on the control treatment.