LIME STABILIZED SLUDGE TREATMENT OF ACID SOILS RELATIVE TO SOIL ACIDITY MINIMUMS FOR SLUDGE APPLICATION

Lime stabilized sludge (LSS) from wastewater treatment plants contains lime, which may neutralize soil acidity, and P, an essential plant nutrient. Guidelines for use of land application of secondary sludges call for the soil pH to be at 6.5 or above prior to application. This greenhouse study was initiated to determine the effects of placement of LSS from two sources on soil and plant parameters of three test species grown on two soils each limed and unlimed. Test crops were radish (Raphanus sativus L.), tall fescue (Festuca arundinacea Shred), and red clover (Trifolium pratense L.). An objective was to determine the need for a pH greater-than-or-equal-to 6.5 prior to application of LSS. Aliquots of two acid soils were limed and left unlimed. The soils were potted after receiving the equivalent of 57,000 kg ha-1 of either dairy or municipal LSS placed in the 2,500 g of potted soil. One crop of radish and two cuttings of the forages were taken. Placement did not affect dry matter yields but the municipal sludge treated plots yielded significantly more dry matter. Liming prior to treatment lowered the Cd concentration in radish and red clover tissue but increased the Cd concentration in tall fescue from the soil having the greatest extractable Cd prior to treatment. Incorporation of LSS into the soils tended to reduce Cd concentration in the plants.