Dynamic composting optimization through C/N ratio variation as a startup parameter

Summary

Different organic wastes (waste of tomato leaves and stems, sheep manure, olive mill waste and melon waste) were mixed with different proportions for different C/N ratio to make better use of tomato waste as it constitutes the majority of horticultural waste in the Souss-Massa region (south-western of Morocco). The objective of this study was to evaluate the effect of C/N ratio on the physicochemical parameters during aerobic composting process (temperature, relative humidity, pH, EC...), and the quality of the compost. The effect of each produced compost was also tested by its incorporation at different rates into sandy soil. The four studied C/N ratios (treatments) were: C/N=25; C/N=30; C/N=35 and C/N=40. Results revealed that the treatment C/N=35 has resulted in the highest oxygen consumption and also, the longest thermophilic phase. Treatments C/N=25 and C/N=35 have reached optimal C/N ratios at the end of the process (respectively 11.88 and 14.71), while treatments C/N=30 and C/N=40 stood higher than 15 (respectively 17.93 and 18.84). Fulvic acid evolution remained constant for all treatments, whereas humic acid content has reached highest levels with C/N=25 and C/N=35 treatments. The effect of compost on seed germination test and phytotoxicity test showed that treatment C/N=35 has produced the most mature compost with the lowest phytotoxicity effect. The amendment of compost has reduced the pH, increased the EC, and enriched soil with organic matter as far as the rate of the amendment is increasing (10; 20 and 30Tonnes.ha-1). Compost of treatment C/N=40 has recorded the highest soil total organic matter content poorly decomposed during composting. However compost of treatment C/N=35 has resulted in the lowest soil total organic matter content, this is mainly due to the intense degradation of the compost during the composting process. The quality of the produced compost depends largely on the level of C/N startup ratio and also the quality of its constituents within the mixture.