Long-Term Maize,Sorghum, and Millet Monoculture Effects on an Argentina Typic Ustipsamment

Maize, sorghum, and millet monoculture effects on soil properties of a Typic Ustip samment in the semiarid pampa of Argentina were evaluated after 27 years in a plot experiment. A permanent Eragrostis curvula pasture was used as a reference. Millet was the most destructive crop to the soil because it decreased dry aggregate stability by 10%, soil organic matter (OM) by 30%, extractable K by 20%, available P by 44%, inorganic P by 11%, available Fe by 20%, available Zn more than 90%, available Cu by 30%, and available Mn by 26%, and it increased wet aggregate instability by 75%. Grain sorghum was less destructive to the soil than millet because it only decreased OM by 30% and extractable K by 24%. All studied crops decreased the cation exchange capacity of the soil between 20 and 30%, the pH values, and the concentration of soil extractable Mg2+by 38 to 63%. Soil extractable Ca2+ was decreased 30% by the Eragrostis pasture and 40% by maize. The negative effect of millet and grain sorghum on OM was attributed to a low coverage of the soil with plant residues left by these crops as well as the long exposition of the bare soil during temperate and wet periods. Decreases of soil nutrient contents were attributed to plant uptake in all cases, except the Zn concentrations, which were related to variations on soil pH and phosphate concentrations. It was concluded that maize, the most commonly cultivated crop in the region studied, did not affect physical and chemical soil properties to a large extent. Conversely, millet had the most negative effect on physical and chemical properties of the soil.