SEWAGE SLUDGE COMPOST AS A SOIL AMENDMENT FOR HORTICULTURAL CROPS

Abstract

Municipal sewage sludge, previously amended with Eucalyptus tree trimmings and composted, was incorporated to a depth of 30 cm at rates of 0, 12.3 and 24.6 dry MT/ha for a field planting of onion, snapdragon, turf and spinach. In a similar subsequent planting, the sludge compost was incorpoated to a depth of 10 cm. Additional treatments address the residual effect of the material. The results indicated sludge compost incorporated to a depth of 30 cm had no effect on crop yields, but when incorporated to a depth of 10 cm there was a significant increase in yields for all test crops. No buildup of heavy metals, soluble salts or changes in soil pH that would depress crop growth were detected. Two greenhouse experiments employed equivalent rates and the same four crops. Two materials, sludge compost and heat-dried sludge were compared. The former contained composted Eucalyptus tree trimmings. The latter did not. The results showed both materials were equally beneficial to crop growth and the presence of Eucalyptus trimmings did not decrease yields