Soil compaction is related to management practices in the semi-arid Argentine pampas

The physical properties of coarse-textured soils in semi-arid regions often deteriorate with use. We hypothesize that compaction is related to the cropping systems employed in accordance with the different water balances of the soils. Surface samples of 52 Entic Haplustolls under three different regimes (24 under continuous cultivation, 18 under rotation with grass leys and 10 virgin soils) were analysed for clay, silt, organic matter and water content, bulk density, resistance to penetration, hydraulic conductivity and susceptibility to compaction. Data were statistically analysed using regression equations and soils were distinguished on the basis of organic matter content and susceptibility to compaction. In soils of similar texture we found resistance to penetration and susceptibility to compaction to be inversely related to organic matter content and therefore higher under continuous cultivation. Hydraulic conductivity was lower in cultivated soils, especially those with a fine texture. The results show that in sandy to loam soils an increase of about 5 g kg(-1) organic matter is required to achieve a 0.06 Mg m(-3) decrease in bulk density at the proctor optimum. The results also indicate that the loss of organic matter occurring in the cultivated soils of the study region makes them more susceptible to compaction, which not only has adverse mechanical effects on plants but also gives rise to a considerable reduction in hydraulic conductivity. (C) 1999 Elsevier Science B.V. All rights reserved.