Carbon and nitrogen storage and organic fractions in latosol submitted to different use and management systems

The advance of the agricultural frontier, characterized by the conversion of natural ecosystems into cultivated areas, was intensified in the last decades. Most of the practices used to manage soils cause changes in the soil quality and soil organic matter (SOM) dynamics. Studying the impact of different management systems is essential to choose the most adequate soil management practices. This study aimed to evaluate different SOM fractions and carbon and nitrogen storage of a very clayey typic dystroferric Red Latosol (Oxisol) under the following use and management systems: native forest (MTN), eucalyptus (EUC), pine (PIN), pasture (PAS), corn under minimum tillage (MCM) and corn under conventional till (MPC). The soil samples were collected in September 2004, in the 0-10, 10-20 and 20-40 cm layers to assess organic carbon (OC) and total nitrogen (TN) storage, in the 0-5 and 0-10 cm layers for the physical-densimetric SOM fractionation, and at 0-5 cm to measure the carbon content of the microbial biomass (Cmic). OC storage in the EUC soil was higher than in the MTN soil. The relative contribution of C increased in the order: C-clay > C-silt > C-sand > C-LF. The largest proportion (> 90 %) of OC was associated to the heavy fraction of SOM, with values close to 98 % in the tillage systems with corn (MPC and MCM). The Cmic and C-light fraction (C-LF) were more sensitive to evaluate changes in SOM dynamics caused by the different use and management systems of the studied Latosol.