PLANT-QUALITY AND SOIL RESIDUAL FERTILITY 6 YEARS AFTER A COMPOST TREATMENT

The final results of a 6-year pot experiment on the organic fertilization of sunflower crops using compost prepared front vegetable and animal wastes are reported Comparisons were made of the plant quality and residual fertility of different soil-fertilizer-compost mixtures ranging from untreated soil (no fertilizer or compost additions) to a 5% soil-95% compost mixture. Crop yields, together with the percentage dry matter, protein, and lipids in the seeds were taken as a measure of plant quality, whereas residual fertility was indicated by the microbial and plant nutrient content of the soil-fertilizer-compost mixtures. After 6 years of cropping with no additional mineral or organic fertilization, improvements in crop yield were still apparent in the mixtures with the highest compost contents. The improved crop production was related to the persistence of improved conditions of residual fertility. It is concluded that the use of compost can lead to improved soil fertility, even after several years, which in turn results in a quantitative improvement in crop yield and product quality.