SOIL ORGANIC-MATTER PARTICLE-SIZE FRACTIONS IN SOILS OF THE SEMIARID ARGENTINEAN PAMPAS

Because the level of organic matter in soils can reflect the intensity of soil utilization, the present study was carried out with the aim o f elucidating the precise effects of different soil management practic es on total organic matter and its particle size fractions in soils of the semiarid pampa region. Surface samples of 52 entic Haplustolls un der three different uses (24 under continuous cropping, 18 under rotat ion with grass leys and 10 virgin soils) were analyzed in terms of cla y, total organic matter content and organic matter particle size fract ions, The obtained data show that organic matter fractions differ acco rding to particle size distribution and the prevailing soil management system, Stable organic matter content (< 50 mu m) is significantly re lated to clay content, whereas coarse organic matter (> 100 mu m) is s trongly influenced by the type of soil management utilized.