LEACHING OF COMPOSTS FROM AGRICULTURAL WASTES TO PREPARE NURSERY POTTING MEDIA

The leaching of salt and mineral elements from three composts prepared with residual vegetable crop biomass (melon, pepper or zucchini) and from one limed peat (control) was studied using methacrylate columns and distilled water. After 5 container capacities of effluent, both the electrical conductivity and the concentration of soluble elements in compost leachates decreased substantially and equalled those of peat. Composts reacted differently to the leaching of salt due to differences in the raw waste sources and the composting process and hence, in their physical and chemical characteristics, especially organic matter contents. At the end of the experiment, after pouring 8 container capacities of water, the leaching efficiency of the salts was 84%, 89% and 77% for melon, pepper and zucchini-based composts, respectively. Mineral elements differed in their ability to be removed from the composts; available N (NH₄⁺ and NO₃^-), K⁺, Na⁺, Cl^-, and S were leached readily, whereas P, Ca²⁺, and Mg²⁺ were removed hardly due to chemical binding or adsorption. Leached composts showed a range of physico-chemical and chemical parameters suitable for use as growing media constituents. Finally, special emphasis must be paid to the management of the effluents produced under commercial conditions to avoid environmental pollution.