Soil quality indicators in conventional and conservation tillage systems in the Brazilian Cerrado

Conventional and conservation tillage systems can alter soil aggregation and total and labile soil organic matter (SOM) contents. This study aimed to determine the degree of soil aggregation, quantify total carbon (TC), permanganate oxidizable carbon (POXC), light organic matter (LOM), and potentially mineralizable carbon (CO2-C) contents in soils aggregates, and assess soil quality indexes at sites under conventional and conservation tillage in the Cerrado region of Minas Gerais State, Brazil. Four experimental areas were analyzed: a area under conventional tillage for 20 years, a area under no-till for 6 years, a area under no-till for 18 years, and a reference area of undisturbed Cerrado vegetation. Soil aggregates retained on 8.0-4.0 mm sieves were evaluated for size class distribution and mean weight diameter. TC, POXC, LOM, daily and Total CO2-C emissions were also analyzed. These data were used to calculate the C/N ratio and sensitivity, carbon pool, and lability indexes. The results of SOM compartments were in agreement with those obtained for the soil aggregation status. 6NT and 18NT had a higher proportion of macroaggregates and higher MWD values than CT in both layers. For other classes of aggregates, CT had the highest proportions of mesoaggregates at 0-0.05 m depth and microaggregates at 0-0.10 m depth. At 0-0.05 m depth, TC and LOM contents were highest in 6NT and 18NT aggregates. In comparing the soil indexes of managed areas, we found a similar pattern to that observed for macroaggregates, MWD, TC, and LOM. CA, 6NT, and 18NT aggregates had the largest CO2-C cumulative emissions at the end of the incubation period. Environmental conditions at no-till areas promoted macroaggregate formation and preserved TC and LOM contents, resulting in a high degree of aggregate stability. Soil quality indexes were sensitive to identify changes between the reference area and managed areas. Soil aggregates from no-till areas had higher CO2-C emissions and cumulative emissions than those from the conventional tillage area.