International Symposium on
Drylands Ecology and Human Security
Application of Sewage Sludge to Improve Soil Physical Properties
Department of Soil Science, Isfahan University of Technology, Isfahan, Iran
Soils in arid and semiarid regions in general have poor physical properties and their water holding capacity is very low. Application of sewage sludge to soils as organic amendment is known to improve soil physical properties such as aeration, bulk density and infiltration. These improvements, however, may bring about potential environmental problems as soil transport properties are also enhanced, increasing the risk of groundwater pollution through leaching of chemicals such as nitrates. The effect of incorporating sewage sludge at rates of 25, 50, and 100 Mg ha-1 in the plow layer of a Haplargid in central Iran on selected soil physical and transport properties was investigated. Wheat was planted after sludge application. The experiment was conducted using a complete randomized block design with three replications. The objective was to evaluate the temporal effect of sewage sludge on selected soil properties measured 23, 85, 148, 221, 351, and 561 days after the treatment. Nitrate concentration was measured to a depth of 180 cm at the end of the wheat growing season. Sewage sludge application significantly increased the average size of the soil aggregates, hydraulic conductivity, final infiltration rate, and moisture content at 33 and 1500 Kpa, while significantly decreasing the soil bulk density. In general, the effects were more evident in the 100 Mg ha-1 treatment. Over time, however, the soil physical properties under various treatments approached the control values. Nitrate movement was significantly greater in the sludge treated plots and significant amounts of NO3 had moved below the root zone. The results of this study indicate that sewage sludge application improves soil physical conditions, with the effects persisting over a long period. However, soil transport properties also change, causing NO3 to move well below the root zone. Because of the higher risk of groundwater contamination, large-scale use of sewage sludge to fields should proceed only with caution.