COFFEE SILVERSKIN AND EXPIRED COFFEE POWDER USED AS ORGANIC FERTILIZERS

The coffee industry produces a wide range of organic wastes, some in large amounts, and most of them do not have a well-defined final disposal. The agricultural use of these wastes can be based on the recycling of nitrogen, but their chemical characterization and evaluation with soil under controlled conditions are mandatory. The aim of this work was to evaluate the use of coffee silverskin and expired coffee grounds as organic fertilizers. The wastes were chemically characterized according to CONAMA’S resolution No. 375 and passed through Brazil’s Agriculture Ministry regulation for organic fertilizers and soil conditioners. A greenhouse experiment with Rhodic Ferralsol soil and maize was performed to obtain the agronomic efficiency index (AEI) for nitrogen. The treatments were control (without residue), ammonium nitrate as a mineral reference, and both organic wastes, at a dose of 450 mg of Kjeldahl nitrogen per pot, in triplicate. The data obtained in the characterization were favorable to the wastes as nitrogen sources for agriculture. However, the AEIs obtained were low (0.5 and 7.9% for the expired coffee grounds and the coffee silverskin, respectively) compared to that of the mineral reference (92%). Based on these results, the use of coffee silverskin and expired grounds as organic fertilizers is not recommended but can improve soil attributes and serve as a complementary source of nitrogen and potash.