Conversion of rural abattoir wastes to an organic fertilizer and its application in the field cultivation of tomato in India

Sophisticated capital intensive waste-recycling technologies are unviable in small rural abattoirs in India due to low volume of wastes (principally blood and rumen digesta) generated and lack of infrastructural facilities. We report recycling of slaughterhouse wastes as an organic fertilizer, ‘bovine-blood-rumen-digesta-mixture’ (BBRDM). Bovine blood and rumen digesta were mixed in 3:1 ratio in a metallic container, boiled and stirred continuously till the mixture was largely free of water. The mass was sun-dried for 3 days to obtain the final product. BBRDM was applied for field cultivation of tomato (Lycopersicon esculentum L., local variety ‘Patharkuchi’) in West Bengal state (India) during 2012–13 and 2013–14. We compared tomato yields obtained with BBRDM (N:P₂O₅:K₂O 30.36:1:5.75) and conventional inorganic fertilizers [diammonium phosphate (DAP), N:P₂O₅:K₂O 18:46:0 + potash, N:P₂O₅:K₂O 0:0:44]. BBRDM was applied at a higher rate compared with DAP + potash to meet the farmers’ desire for enhanced yields. 75 kg ha⁻¹ was applied at the 2nd week while 150 kg ha⁻¹ was applied at the 8th week after transplantation. Yields (total fruit weight) obtained from BBRDM-treated plants were higher in comparison with DAP + potash-fertilized plants by 46–48% as the former supplied 2.5 times more nitrogen (N) than the latter. The partial factor productivity of DAP + potash was 73–76% higher than BBRDM. Conversely, as BBRDM was produced through local entrepreneurship from slaughterhouse wastes, the cost of this organic product would be expected to be much lower than the commercial inorganic fertilizer. Furthermore, application of BBRDM negates the environmental cost of treating slaughterhouse effluent. Considering the same cost of applying 225 kg fertilizer ha⁻¹, higher yield with BBRDM should result in greater potential revenue for the farmer compared with yields with DAP + potash. The C/N ratio of BBRDM is 4.8, having relatively high N content. Accordingly, rapid release of plant-available N was observed in BBRDM-fertilized soils. The temporal increase in soil NH₄ ⁺may be attributed to lack of soil N immobilization. Local farmers are willing to accept the new fertilizer as a substitute for currently used chemical fertilizers.