EVALUATION OF STABILITY AND MATURITY OF COMPOSTED RICE STRAW, OLIVE POMACE AND SOME AGRICULTURAL WASTES

Abstract

Composting technique is considered as one of the environmentlly friendly methods used for recycling the excess residues of rice straw ( RS) and solving the environmental problems of olive pomace (OP) by-product of the olive oil industry. For this purpose, three compost piles were made from mainly rice straw, different ratios of olive pomace and some agricultural wastes viz. tomato hallum, banana residues and farmyard manure to evaluate the stability and maturity of composted materials during 90-day composting period. The first pile (A) was made of 60% RS+10% OP+10% tomato hallum+10% banana residues+10% farmyard manure, the second pile (B) wase made of 50% RS +20% OP+10% tomato hallum+ 10% banana residues+ 10% farmyard manure while the third pile (C) was made from 40% RS + 30% OP10% tomato hallum+ 10% banana residues+ 10% farmyard manure. Representative compost samples were taken after 15, 30, 45, 60 and 90 days of the composting process. The results revealed that slight increase in temperature occurred through the first 2-3 days of composting to reach the maximum values at 30 days of composting (thermophilic stage). All the composts showed a more pronounced increase in pH, EC, bulk density and total nitrogen, while total organic carbon significantly declined with composting progress. Consequentially, the C/N ratios became narrowed during composting process where they reached 18.80 for pile C. At maturity stage, the greatest values of humification parameters (Humification index, Humification degree and Humification rate) were obtained by pile C followed by pile B. Meanwhile, the ratio of NH4+/NO3- as an indicator to nitrification process, Extinction coefficient (E4/E6) as well as CO2 rate decreased gradually to reach the minimum values. Finally, the highest values of germination index (92.22 and 95.39%) were achieved with pile C for cress and barley seeds, respectively