Biochar e sua influência no solo, nas plantas e na dinâmica do carbono

Abstract

The application of biochar to degraded or highly weathered soils has been recommended in several countries with climate regions vulnerable to environmental problems but requiring high agricultural productivity to meet population demands. This technology stimulates the circular economy through the use of various organic residues and supports both traditional and regenerative agriculture. This study evaluated the effect of different types of biochar on soil properties, microbiota, plant growth, and the distribution of carbon and nitrogen among soil particle-size physical fractions. The first experiment, conducted in a randomized block design in an agricultural greenhouse, assessed the effect of four types of biochar (pear orange bagasse – BL, sugarcane bagasse – BC, corn cob – BM, and green coconut residue – BCV) on some chemical and biological properties of a Red-Yellow Ultisol and on the growth of curly mustard (Brassica juncea L.). All biochars increased soil carbon (by 108–175%) and total phosphorus (by 22–38%) concentrations. However, the biochar type affected total nitrogen and exchangeable calcium concentrations, as well as microbiota behavior and plant biomass, confirming findings reported in the literature on the importance of evaluating the effects of different biochars. The second study, conducted in a completely randomized design in the laboratory, evaluated the effect of three types of biochar (dry coconut residue – BCS, pear orange bagasse – BL, and biosolid – BB) on the distribution of carbon and nitrogen in the particulate organic matter (POM) and mineral-associated organic matter (MAOM) fractions of a RedYellow Ultisol after a three-year incubation. The biosolid biochar had the smallest contribution to increasing soil carbon (40%) but stood out as the best nitrogen source, increasing soil N content by 145%. This effect is clearly associated with its chemical composition. In general, the biochars did not affect the proportional mass of the POM and MAOM fractions but caused significant changes in the distribution of C and N between them, with a proportional increase of C in the POM and a reduction in the MAOM. In soil without biochar, 17% and 85% of carbon were distributed in the POM and MAOM fractions, respectively. However, biochar increased C in the POM by 4.5 (BB) to 8 times (BCS and OB), causing a shift in the carbon proportion between the two fractions. These results complicate the use of particle-size physical fractionation of organic matter as a tool for assessing changes in soil quality due to management practices, as the POM fraction is no longer a reliable indicator of carbon lability in biochar-amended soils.