Tillage systems effects on soil carbon stock and physical fractions of soil organic matter

Changes in soil management and land use influence soil organic matter (SOM) turnover through changes in quantity and quality of plant residues entering the soil, their seasonal and spatial distribution, the ratio between above- and bellow-ground inputs and through changes in soil disturbance. We hypothesized that the sequestered C is stored mainly in the mineral associated fraction (C associated in sand, silt and clay fraction). The objective of this study was to evaluate the C stock and stabilization in a tropical Dystrophic Red Latosol (Typic Haplortox) (Paty do Alferes, Brazil) subjected to 6-years soil tillage systems and soil cover. Treatments included no-tillage (NT), animal traction (AT) and conventional tillage (CT). Two additional treatments were evaluated: grass coverage (GC) and bare soil (BS). After six years crop, soil C stock in the 0-10 cm layer was higher in NT than in CT (17.6 vs. 12.3 Mg ha−1, P < 0.05). It resulted an increase of 5.3 Mg C ha−1 in NT when comparing to CT. In NT, most of the C accumulation compared to CT occurred in the mineral associated fraction. Although, only the C associated in sand fraction was statistically different (6.7 vs. 1.2 g kg−1 soil, P < 0.05). GC had the highest C sequestration and C and N associated in the mineral fraction (14.9 g C kg−1 and 5.1 g N kg−1) in the 0-5 cm depth. For all treatments, most of the soil organic C was in the heavy fraction (> 55%). GC incorporated to soil annually 0.6 Mg C ha−1. C associated with sand fractions was the most sensible mineral associated C fraction compared to C in silt and clay fraction, and can be used as a suitable soil quality indicator for sustainable use.