Four agricultural residues namely, sheath of peanut pods, flax shivers, red sawdust and white sawdust, were composted with different amendments for four months under greenhouse and field conditions. Results emphasized that composting proceeded at different rates and was principally influenced by the type of residues and/or added amendments. Initial bio-fortification of residues with cellulose decomposing microorganisms, exhibited a recognized trend of stimulation and led to a higher rate of organic carbon loss. Percentage losses in organic carbon of the sheath of peanut pods after composting were higher in biofortified treatment. The organic accelerator associated with bio-fortification, led to a loss in the organic carbon amounting to 15.61% of the initial value of flax shivers, after 120 days of composting. Bio-fortification of red sawdust receiving either an organic or a chemical accelerator increased the amounts of bio-oxidized organic carbon to 9.13% in the control and to 16.45 or 12.97% respectively, in amended red sawdust. In white sawdust, the differences in the percentage of oxidized carbon were hardly detectable. The nitrogen (N) concentrations increased in the final compost and the largest amount was found in the sheath of peanut pods, reaching 2.6%. The level of total nitrogen was more or less the same in composts prepared from either flax shivers, red or white sawdust where it was 1.65, 1.63 and 1.5%, respectively. Oxidation of organic matter associated with the increase in nitrogen concentrations, whether initially or during composting, led to a reduction in carbon/nitrogen (C/N) ratios in the final composts. Generally, all biofortified composts had narrower C/N ratios compared to the non-biofortified ones. The lowest organic carbon and total nitrogen contents and consequently C/N ratios were found in sheath of peanut pods compost compared to other residues. Initial neutral pH values of different composted residues were slightly shifted towards acidity before settling around neutrality. Total soluble salts in the final composts varied within the type of agricultural residues used. Nevertheless, values in all composts at the end of the composting did not exceed safe levels.
Key words: Potting soil, bio-fortification, composting, agricultural residues and cellulose decomposing microorganisms.
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