POTASSIUM AVAILABILITY WITH APPLICATION OF SEWAGE-SLUDGE, AND SLUDGE AND MANURE COMPOSTS IN-FIELD EXPERIMENTS

An experiment was conducted to determine the plant availability of K i n organic wastes. Four materials: digested sewage sludge (DSS), digest ed irradiated sludge (DISS), digested, irradiated and composted sludge (DICSS), and composted livestock manure (CLM) were applied to farmlan d for two years at rates of 10, 20, 30, and 40 mg-solids ha(-1) yr(-1) . Potassium fertilizer (KCl) was added to the control treatment (CT), to which no waste was applied, and to the low-rate waste applications, to meet crop K requirement. Equal yields within different treatments were obtained for the test crops lettuce and snap beans through applic ation of available N at the levels balanced for crop economical produc tion. Potassium from the wastes was evaluated based on the assumption that Crop K uptake/Available K applied was equal between the CT and wa ste treatments. The results indicated that, in general, K applied with wastes (waste K + fertilizer K) was equally available (101 +/- 7%) to fertilizer K (KCl), except for low rate application of DISS (10 Mg ha (-1)), where the availability of K was low (89 +/- 1%).