Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management

Evaluation of aggregate formation in no-till farming systems and the effects on soil organic matter can provide relevant insights into soil carbon storage, nutrient cycling, and soil susceptibility to erosion. However, there is little information on the soil aggregate formation pathways in no-till systems. This study aimed to investigate the effect of no-tillage duration on soil aggregates and soil organic matter compared with undisturbed soil in the rainy and dry season. The following experimental sites were analyzed: NT2 (no-till management for 7 years), NT14 (no-till management for 14 years), NT23 (no-till management for 23 years) and AF, a preserved fragment of Atlantic Forest (reference area). Aggregate formation pathway was analysed/described according to the morphological pattern using a stereo microscope (LEICA M125), in magnification ranges between 20x and 40 x. Physical fractionation of organic matter was carried out by granulometric size separation, and humic substances were separated into humic acid, fulvic acid, and humin fractions by differential solubility. No-till management affected the dynamics of soil aggregation and organic matter fractions. In the long term, no-till farming reduced biological aggregation (52.5 +/- 4.5 % in AF to 19.2 +/- 3.1 % in NT23), and increased physicochemical aggregation (21,2 +/- 2.1 % in AF to 47.2 +/- 5.1 % in NT23), may be because the traffic-induced compaction resulting from seeding. However, over the years, no-till farming increased soil particulate organic carbon (POC), mineral-associated organic matter (MAOM) and humin contents because of the constant input of crop residues to surface layers. Our results suggest that the morphological classification analysis of soil aggregates was sensitive to changes in land use over time, consisting as an indicator practical, affordable, repeatable, and easily understood and interpreted, which may be used to ascertain changes in physical soil conditions.