Organic matter and soil aggregation in agricultural systems with different adoption times

In conservation management systems, such as no-till (NT), it is important to analyze the pattern of changes in soil quality as a function of the time since adoption of the system. This study evaluated the physical fractions of organic matter and soil aggregation in management systems in areas cultivated with different times since implementation of NT: 6, 14, and 22 successive years of soybean and maize/wheat crops (NT6, NT14, and NT22, respectively); 12 years of no-till with successive years of soybean and maize/wheat crops, and the last 4 years with integration of maize and ruzi grass (Brachiaria ruziziensis) - (NT+B); pasture; and forest. Physical fractionation of organic matter determined the total carbon (TC), particulate organic matter (POM), and mineral organic matter (MOM) by calculating the carbon management index (CMI) and variables related to soil structural stability. Forest and pasture areas showed the highest contents of TC, POM, and MOM, as well as higher stocks of POM and MOM. Among the cultivated areas, higher TC and particulate fractions of organic matter and the best CMI values were observed in the area of NT22. There were changes in aggregation indices, depending on the time since implementation of NT. Areas of NT22, pasture, and forest showed the greatest evolution in C-CO2, indicating increased biological activity, with positive effects on soil structural stability.