Nutrient dynamics and decomposition rates during composting of sulphitation pressmud by different methods

Decomposition rates and nutrient contents of sulphitation pressmud (SPM), either alone or by mixing with cow dung and rice straw, under the aerobic (heap and NADEP), anaerobic (pit) and vermicomposting methods were compared. Loss in Organic C and C/N ratios of the decomposing materials indicated the heap and NADEP methods faster for the composting of SPM alone and SPM + cow dung and vermicomposting method for SPM + rice straw registering significant reductions in Organic C ranging from 45.0 to 61.0% from the respective decomposing materials at termination time (119 days). The heap and NADEP methods recorded C/N ratio of SPM alone as low as 11 and 12 and SPM + cow dung as 12.0 and 13.9 at termination stage. Vermicomposting method brought the C/N ratio of SPM + rice straw to 16.4 as compared to 18.6 to 29.8 with the other methods. Irrespective of the composting methods, CO2 evolution from the decomposing materials was higher in early period (up to 28 days). Among methods, NADEP and heap methods recorded more CO2 evolution in early period while vermicomposting method showed more CO2 evolution at the later intervals in comparison to the other methods. Nutrient content in the decomposing materials at different intervals depended on their initial contents. Total N in the composts were statistically comparable, however, the composts of SPM alone recorded relatively more N than SPM + cow dung and SPM + rice-straw prepared by the respective methods. Total P and K contents of the composts increased with time irrespective of the composting methods. Composts of SPM alone recorded significantly more total P than SPM + cow dung and SPM + rice straw at 62, 91 and 119 days while SPM + rice straw recorded more total K than the composts of other materials. Total P in the composts did not differ with the composting methods, but total K in composts of SPM alone was relatively more with heap and NADEP methods, in SPM + cow dung with pit method and in SPM + rice straw by vermicomposting method. Total S in the composts decreased with time and both the aerobic methods showed more reductions than pit and vermicomposting methods.