Scanning electron microscopy for analysing maturity of compost/vermicompost from crop residue spiked with cattle dung, Azolla pinnata and Aspergillus terreus

Rice straw and wheat straw were mixed with cattle dung (C), Azolla pinnata (A) and Aspergillus terreus (F) and subjected to aerobic composting and vermicomposting. Eight different mixtures were made as R, RC, RA, RF, RCF, RCA, RFA and RCFA and W, WC, WF, WA, WCA, WCF, WFA and WCFA. Ratio of straw and cattle dung was kept as 2:1, and weight of cattle dung was reduced proportionally when Azolla (20 g) or fungus (20 ml) was added in a mixture. Surface structural morphology of the initial and final mixtures was analysed with SEM. Initial samples showed larger particle size with a coarse surface, less compaction and arrangement of biomass as a dense meshwork of lingo-cellulosic fibres. Final samples showed smaller particle size, compaction and several pores per unit area. Electron micrographs clearly show enhancement of degradation and better texture with the addition of fungus, Azolla or cattle dung to the straw. Azolla and cattle dung when added separately, enhanced degradation and compaction, but the mixtures with fungus showed degradation with no compaction. Maximum homogeneity and smallest particle size of RCFA and WCFA indicated that addition of Azolla and fungus along with cattle dungenhanced degradation of straw and enhancement was remarkably more when the mixtures were subjected to vermicomposting. This is a first report highlighting vermicomposting of the straw mixed with Azolla and fungus along with cattle dung for obtaining a better quality product suitable for agricultural use. Parallel variation in C/N ratio and nutrient profile of the mixtures show that SEM helps in determining maturity index of composts.