• Grazing effects of the bulk density in a Natraquoll of the flooding pampa of Argentina

      Taboada, M. A.; Lavado, R. S. (Society for Range Management, 1988-11-01)
      The influence of grazing by cattle on soil bulk density was studied in a typic Natraquoll of the Flooding Pampa of Argentina for a period of 33 months, by comparing a grazed situation to an enclosure deferred from grazing for 7 years. Floods took place in this period as usual. Bulk density (BD) at -33.3 kPa of water retention varied from 1.00 to 1.11 Mg m-3 in the ungrazed soil and in the grazed soil from 1.04 to 1.16 Mg m-3. Environmental factors were the primary agent controlling BD; only in some periods were there significant differences between treatments. Slight increases in BD occurred under grazing after the recession of the flood water, and significant decreases occurred in the ungrazed soil during the large and sudden falls in water content. In this case the effect of trampling, therefore, would consist mainly of impeding the decrease in BD. No compaction was observed in periods when no flood occurred or while soil remained submerged in water. The results indicated that the variations of bulk density caused by cattle trampling were superimposed on those produced by floods and showed an interaction between the effects of land-use and the particular environmental conditions of the region.
    • The deterioration of tall wheatgrass pastures on saline sodic soils

      Taboada, M. A.; Rubio, G.; Lavado, R. S. (Society for Range Management, 1998-03-01)
      The deterioration of sown tall wheatgrass (Elytrigia elongata) growing on 3 sodic saline soils was investigated in the Laprida basin, in the center of the Buenos Aires province of Argentina. These soils are known to have poor drainage and high saline levels and support different species associations. On each soil type the native grassland was compared to sown wheatgrass, in terms of plant density and cover and soil physical and chemical characteristics. The 3 soil types reacted differently to tillage. Tillage had little impact on soil type A (typic Natraquoll), a poorly drained soil with a loamy A horizon (14 cm) overlying a silty clay loam. Soil type B (typic Natraquaf), a wet texture contrast soil with bleached horizons has characteristics that are likely to severely limit plant growth. The sowing of wheatgrass increased ground cover by live vegetation on this soil type. This contrasted with soil type C (typic Natralboll), a saline soil with an organic matter-rich but thin (8 cm) A horizon. In this soil, the plant density declined and other components such as pasture cover also declined with time. This pasture deterioration was attributed to several soil factors including decreased organic matter content and increased soil bulk density. It was concluded that the varied performance of wheatgrass sown pastures was a function of the different inherent characteristics of the soils.