Tolerance of forage legumes to lime-stabilized sludge

Lime-stabilized sludge (LSS) from dairy processing waste-water treatment plants is a desirable product for land application. The material contains lime, which neutralizes soil acidity, and P, which is useful as a plant nutrient. The fineness of the lime and the solubility of P make LSS especially desirable in establishing forage legumes. This greenhouse study had two objectives; to determine a reasonable quantity of LSS for establishing forage legumes such as alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.) and to prevent adverse effects on seedlings. Sludge was applied at 0, 2.5, 5.0, 7.5 g kg^-1to an acid, low P soil in pots, and alfalfa and red clover seeds were sown. All treatments received 123 pg g^-1potassium as KC1. A completely randomized design with four replications was used. Each species was handled as a separate study. Dry matter production was measured at one-tenth bloom stage. Plant samples were analyzed for P, K, Ca, and Mg content. Soil samples taken at the end of the study were analyzed for pH, organic matter, Bray P, K, Ca, Mg, exchangeable Al, EC, and CEC. The higher quantities of LSS (7.5 g kg^-1for alfalfa and 5.0 g kg^-1for red clover) had negative effects on seedling germination and establishment. Lime-stabilized sludge resulted in an increase in total nutrient uptake of Ca, Mg, K, and P up to 5.0 and 2.5 g kg^-1in alfalfa and red clover, respectively. In both species significant dry matter yield increases were obtained with LSS up to 5.0 g kg^-1; however, 7.5 g kg^-1caused a reduction in dry matter yield. Based on these results, applications of LSS at 5.0 for alfalfa and 2.5 g kg^-1for red clover had positive effects in seedling establishment, nutrient uptake, and dry matter production. Lime-stabilized sludge application resulted in significant increases in soil pH, available P, Ca, Mg, EC, and CEC; decreases were seen in neutralizable acidity and exchangeable A1 levels in soil. This study indicates that LSS is appropriate for the acidic, low P soils of Southern Missouri for alfalfa and red clover establishment and production, if applied in appropriate quantities.