M. Sankaranarayanan
The extent of human influence in agriculture on global warming remains hotly debated throughout the world. A firm scientific understanding is needed about the effect of animal manure and inorganic fertilizers on the emissions of the greenhouse gases. The National Domestic Biogas Programme (NDBP) being implemented by Rwanda, Africa has conducted a study on baseline data on fuel use and manure management at the household level emission on GHGs. The main objective of the study is to determine the amount of greenhouse gases (GHGs) emissions that can be reduced through the use of household bio digesters. The three GHG gases are CO2, N2O (nitrous oxide), and CH4 (methane). Agriculture has the potential to serve as a sink for at least one of them, carbon dioxide (CO2). Anaerobic digestion of organic waste conserves nutrients needed for crop production. The only materials removed from the bio-digester system are the gases generated, mostly methane, carbon dioxide and hydrogen sulphide. The study revealed that average total dung produced per day in a household with at least 3 heads of cattle was found to be almost 50 kg/household in Rwanda. The average quantity of dung collected in wet and dry season are 47 and 48 kg/day/household respectively. The average projected biogas yield is 1.60 m3/day/household based on the IPCC biogas yield at 0.032 m3 per Kg of cow dung. It is found that the practice of pasture grazing is not so common in Rwanda. It is found that 85% of households of Rwanda adopt the practice of collecting the solid dung and other organic waste from the cattle shed and takes it to storage pit before transportation to farm spread. It is observed that in Rwanda one family member or one hired labor is used for collection of manure for 3.32 hours/day to collect 67.43 kg manure/day/household. The average time taken to apply manure is 1.9 to 3.2 hours/day/person for the quantity of 41.8 to 82.5 kg/day/person.