Soil Carbon Sequestration Due to Crop Sequences Under No-Tillage in Tropical Region.

No-tillage system (NT) under tropical regions are important for C sequestration, which increase soil quality, but it is dependent of the plants used in crop sequence. The objective of this study was to evaluate the capacity of a long-term NT cropping sequences to increase soil organic C and improve soil aggregation. By nine years were cultivated continuous corn (Zea mays L.) (CC); continuous soybean (Glycine max L. Merrill) (CS); and soybean/corn rotation (SCR) as summer crops and corn, sunflower (Helianthus annuus L.), oilseed (Raphanus sativus L.), millet (Pennisetum americanum), pigeon (Cajanus cajan (L.) Millsp), sorghum (Sorghum bicolor (L.) Moench) and sunn hemp (Crotalaria juncea L.) as winter crops. Soybean on summer (SCR and CS) and sunn hemp on winter increased soil C stock (16.24, 16.30 and 17.24 Mg ha^-1) and soil C sequestration rate (0.68, 0.68 and 0.79 Mg ha^-1 y^-1), which may be attributed to the fast soil C addition by legumes biomass and N availability for the subsequent crop. Pigeon pea and sunn hemp increased total soil N content, when compared to corn under CC. Conversely, corn enhanced total soil N content, compared to pigeon pea and sunn hemp, under CS, showing the importance of intercropping grasses/legumes for the no-tillage system. Increases of soil N content increased soil C. The highest mean weight diameter aggregate (MWD) was observed under SCR. Sorghum increased MWD compared to sunflower, oilseed and pigeon. The MWD correlated with fine particulate organic carbon.