Intermittent evaporation from calcareous sandy soils as affected by sewage sludge

Saudi Arabia produces large quantities of aerobically digested sewage sludge, most of which is being dumped into landfills. Since most agricultural soils in Saudi Arabia are mainly calcareous sandy soils, and low in organic matter, the application of sewage sludge to these soils may be used as a source of organic matter for the improvement of some physical properties of these soils. In a laboratory study, the effect of added sewage sludge in upper depth 10 cm of soil columns at concentrations of 0, 50, 75, and 100 Mg ha(-1) on cumulative evaporation, percentage of water conserved and soil moisture profile of slightly and moderately calcareous sandy soils (Typic Torripsamments) was investigated Thirty-four mm of irrigation water (tap water) was applied every 7 days. Soil columns were placed in a walk-in controlled growth chamber with a constant temperature of 32 degrees C. By the end of the third cycle at the 21st day, sewage sludge concentrations were significantly effective in reducing the cumulative evaporation, with the same trend as in the first and second cycles. Furthermore, evaporation was greater for high concentration (100 Mg ha(-1)) of sewage sludge application than for the low concentration and control. The percentages of water conserved at 25, 50, 75, and 100 Mg ha(-1) were about 1.34, 1.53, 1.71, and 1.84 times those of the control for slightly calcareous sandy soil and were 1.24, 1.48, 1.63, and 1.81 times the control for moderately calcareous sandy soil. For both soils, results indicated that evaporation constants for different sewage sludge concentrations follow the same pattern. The results also showed that the high sewage sludge concentrations gave higher moisture content in soil columns. The results indicated that sewage sludge may be utilized in calcareous sandy soils as an organic amendment to reduce evaporation and increase percentage of water conserved.