Organic-Matter Pools of Soil under Pines and Annual Cultures

When submitted to different uses and managements, soils can suffer alterations in the amount and in the quality of carbon and nitrogen present in the soil. This study's objective was to evaluate carbon and nitrogen in different compartments of the organic matter of the soil under savannah, 30-year-old pine plantation, and annual cultivations with corn and soy under conventional preparation and direct planting after 10 years of age. The substitution of the savannah for the pines and annual cultures reduces the carbon and total nitrogen in the soil. Among the compartments, only the particulate-free light fraction is not reduced in the Pinus in relation to the savannah. No tillage presents potential for improvement of the quality of the soil to make the fractions of carbon more labile in the soil. The more labile fractions reflect the alterations well imposed in the use and management of the soil, and they can be used as sensitive and premature indicators of the quality of the soil. They can be used for calculation of the carbon management index.