Management of organic residues in the coffee productionchain and their impact on soil attributes for the promotion of circular economy

Abstract

The increase in population necessitates higher agricultural production, which in turn produces considerable amounts of organic residue, including agricultural residues. A significant portion of agricultural residues originates from harvest and post-harvest processes. In Brazil, the coffee production chain plays a significant national and global economic role but also generates underutilized residues. In the context of a circular economy, transforming these organic residues can enable their reuse within agriculture. Composting, anaerobic fermentation, and pyrolysis are techniques that can be applied to manage coffee production residues. The application of products derived from these processes, known as soil conditioners, can enhance the effectiveness of conventional fertilizers and improve soil health compared to conventional management systems. The objective of this study is to compare the soil conditioning effects of coffee husk, organic compost, Bokashi, biochar, and COMBI (compost + biochar) on coffee cultivation in two coffee-producing areas (commercial and family farms) in the municipality of Santo Antônio do Amparo, MG, over two production seasons, 2021/2022 and 2022/2023. Biochar was produced through the pyrolysis of coffee husk and wood, while compost and Bokashi were primarily obtained from coffee husk as the main residue. These materials were chemically characterized. The treatments evaluated were: 1) raw coffee husk, 2) organic compost, 3) Bokashi, 4) biochar (coffee husk and wood), 5) COMBI, 6) commercial organomineral fertilizer, 7) conventional fertilization. Application rates of 5 or 10 tons per hectare of soil conditioners were used. Treatments 1 to 5 received conventional mineral fertilizer as a nutrient supplement. The experiment was conducted using a randomized block design with four replicates. Soil analyses, foliar analyses, evaluation of soil bioindicators, and analysis of coffee productivity were conducted. For the chemical attributes, significant differences were observed compared to the control in Area commercial during the 2021/2022 season for calcium and magnesium under the use of COMBI, with concentrations 50% and 46% higher, respectively. Additionally, an effect on base saturation (V%) was noted, with a 24% increase compared to the control. In the 2022/2023 season, the treatment with the most notable results was biochar, which significantly impacted CEC at pH 7.0, showing a 20% increase compared to the control. In Area family farms during the 2021/2022 season, K, P, and remaining P showed increments of 69%, 45%, and 20%, respectively, compared to the standard. For biological indicators in Area commercial during the 2021/2022 season, the application of COMBI resulted in significant differences in MBC and urease activity, with increases of 8% and 21%, respectively, compared to the use of conventional fertilizer. Productivity statistically differed in only one area and for the first harvest according to the treatments used. The management of organic residue in the production of soil conditioners has shown promise, presenting positive effects on the relationships between soil fertility and biology.