The increase of soil organic matter stocks under conservation management systems is dependent of soil type and regional climatic conditions, and has influence on the physical quality of soils. In this study the long-term (21 yr) effect of no-tillage on total soil organic carbon (TOC) and particulate organic carbon (POC, >53mm), as well as its relationship with aggregate stability of a South Brazilian Oxisol (Haplohumox), was evaluated. In comparison with TOC stocks of conventionally-tilled soil, no-tillage soil had a net storage of 0.15Mg ha-1 yr-1 of TOC, and 0.06Mg ha-1 yr-1 of POC, in the 0-20cm soil layer. These low accumulation rates of organic carbon probably were due to the high clay content and gibbsitic mineralogy of the soil, which determine a great physical stability of soil organic matter. The mean geometric diameter (MGD) of soil aggregates varied from 1.6 to 3.7mm, and had a positive relationship with TOC and POC, reinforcing the crucial role of organic matter on physical quality of subtropical oxisols.
conservation management systems; soil organic carbon; soil aggregation
