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.

Selenium (Se) is not considered an essential nutrient for plants, although trace amounts of this element can enhance the growth and yield of some plant species. The application of sodium selenate in staple foods has been proposed as an alternative to minimize Se deficiency in the human diet. However, the threshold between deficiency and toxicity for Se is very narrow. Different plant species vary considerably in the absorption and accumulation of Se in shoots and other edible parts, and also in the tolerance to high Se concentrations in the soil. Therefore, this study aimed to evaluate the Se toxicity in common bean plants grown under high doses of sodium selenate, and the Se translocation of contaminated bean seeds to next generation grains. The study was carried out on a field experiment with the application of four rates of sodium selenate (0, 50, 500 and 5000 g/ha) to the soil were common bean crop was grown. Following, greenhouse conditions were used to investigate the translocation of Se from enriched seeds to the grains. The common bean showed tolerance to sodium selenate rates up to 500 g/ha, with reduction of yield observed at rate of 5000 g/ha. Even with no symptoms of toxicity the application rates of 500 g/ha of sodium selenate to the soil produced grains with concentrations of Se that surpass the limit established by Brazilian food law. The seeds enriched with Se can translocate this nutrient to the next generation.

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