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 cro pping systems employed in accordance with the different water balances of t he soils. Surface samples of 52 Entic Haplustolls under three different reg imes (24 under continuous cultivation, 18 under rotation with grass leys an d 10 virgin soils) were analysed for clay, silt, organic matter and water c ontent, bulk density, resistance to penetration, hydraulic conductivity and susceptibility to compaction. Data were statistically analysed using regre ssion equations and soils were distinguished on the basis of organic matter content and susceptibility to compaction. In soils of similar texture we f ound resistance to penetration and susceptibility to compaction to be inver sely related to organic matter content and therefore higher under continuou s cultivation. Hydraulic conductivity was lower in cultivated soils, especi ally those with a fine texture. The results show that in sandy to loam soil s 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 a lso indicate that the loss of organic matter occurring in the cultivated so ils of the study region makes them more susceptible to compaction, which no t only has adverse mechanical effects on plants but also gives rise to a co nsiderable reduction in hydraulic conductivity. (C) 1999 Elsevier Science B .V. All rights reserved.