ASSESSING THE USE OF COMPOSTED TWO-PHASE OLIVE MILL WASTES AS SOIL IMPROVERS

Abstract

Co-composting two phase olive mill wastes (TPOMW) with bulking agents –which provide nitrogen and aeration– with agricultural purposes is an appropriate strategy for the management of this by-product from both environmental and economic points of view. The aims of this work were to characterize two composts prepared by mixing TPOMW and fresh horse manure and to study the effects of the composts produced when applied to a calcareous soil fertilized with two mineral programs on radish, lettuce and green beans throughout two years, by emphasizing on crops productivity and soil chemical properties. The two mixtures subjected to composting evolved to materials with different properties, thus leading to differences in soil and crop responses to the resulting composts. After compost application radish root and leaf biomass were significantly higher when AL was added compared to AL+H, and similarly standard mineral fertilization (F1) showed higher values for these parameters than the reduced program F2. Regarding subsequent crops, compost application increased markedly lettuce and bean yields in comparison with the controls, especially treatments with the highest rate of compost and mineral fertilizers. Throughout the second year of the experiment, standard fertilization enhanced radish and lettuce productivity, whereas non significant variations in bean pods yield were scored; in addition, the residual effect resulted in a greater lettuce yield in compost-amended treatments with standard fertilization, especially when composts were added at 24 Mg ha-1. Finally, compost application improved soil fertility, particularly by increasing total organic carbon, total nitrogen and available potassium contents with respect to controls.