MAXIMUM RATE OF SOLID PIG SLURRY IN ORGANO-MINERAL FERTILIZER FORMULATION

There is an increasing interest in the recycling of by-products and waste materials with low concentration of nutrients, such as the separated solid fraction of pig slurry with or without composting (SPS), for land application as fertilizers or soil amendments. In Canada, these 'low-analysis` fertilizers are regulated by The Fertilizers Act and Regulations. According to the Canadian Fertilizer Act, % N + % P2O5 + % K2O in a mixed fertilizer (low-analysis fertilizer + mineral fertilizers) should be not be less than 24%. In the context of sustainable agriculture, it is necessary to develop organo-mineral fertilizers (OMF) containing SPS that do not pose a risk of adverse effects to the environment. This study aimed to determine the maximum amount of SPS that can be added to mineral fertilizers in order to obtain an OMF that contain 24% of N+P2O5+K2O. Two commercial mineral fertilizers, monoammonium phosphate [MAP (11-52-0)] and diammonium phosphate [DAP (18-46-0)], and 14 pig slurries were used in this study. The concentration of total N in SPS ranged from 0.9 to 4.3%, P2O5 from 2.3 to 14.2% and K2O from 0.6 to 4.0%. The amount of N+P2O5+K2O varied from 5.2% in SPS obtained by means of flocculation using a polymer + rock dust to 19.1% in SPS obtained by means of flocculation-sedimentation using magnesium by-products. The maximum amount of SPS to be used in mineral fertilizers mixture varied from 68 to 89% by weight of the OMF, depending of SPS type. There is obviously a great deal of research needed to optimize manufacturing starter OMF pellets containing more SPS than ammonium phosphate fertilizers.