Effects of different agricultural systems on organic matter and aggregation of a medium-textured soil in subtropical region

Abstract

This work evaluates the impact of different agricultural systems on the humic fractions of organic matter (SOM) and soil aggregation in a medium-textured soil in a subtropical region of Brazil. Three managed areas and a reference area were evaluated: permanent pasture (PP), no-till (NT), no-till+Brachiaria (NT+B) and native forest (NF). Deformed soil samples were collected in the layers 0-0.05; 0.05-0.10; 0.10-0.20 and 0.20-0.40 m, and unformed soil samples in the layers 0-0.05 and 0.05-0.10 m. After collection, total organic carbon (TOC) analysis, chemical fractioning of SOM and aggregate stability analysis were performed. The PP area presented the highest TOC and C-FA contents in the first three layers evaluated. In the 0.10-0.20 m layer, the C-HUM contents in the NT+B area were 1.9 times higher than in the NT area, and in 0.20-0.40 m they were 6.6 times higher. The PP area obtained the best structural indicators, especially higher WMD, GMD and % of macroaggregates. The two areas using direct seeding presented a percentage of macroaggregates higher than 37.28% in the superficial layer. The PP management provided increases in TOC levels and, consequently, humic substances, besides the formation of more stable aggregates. The NT+B system showed promise in increasing TOC and humic substances, especially at depth, even with a short implementation period. The increase in TOC and humic substances provided by the grasses contributes to the formation of more stable aggregates and, consequently, to the improvement of the quality of medium-textured agricultural soils.
 Keywords: aggregate stability, carbon fractions, climate change, humic substances.