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Effects of Long-Term Cattle Grazing on Structural Stability and Some Chemical Properties of a Seasonally Flooded Vertisol
Abstract
Destruction of soil structure can increase surface runoff with adverse consequences, leading to reduction in the area of land available for crop production. The impacts of long-term grazing by cattle on the structural stability and some chemical properties of a heavy clay soils, periodically submerged by water were studied. Results showed that total organic carbon (TOC) was high in the cattle grazing soil due to contributions from the cattle residues, but the organic residues did not enter into close associations with the soils aggregates. Mean weight diameter (MWD) of water-stable aggregates ranged from 1.16 to 1.13 mm in the cattle grazing soils and between 1.22 and 1.92 mm in the non-cattle grazing soil. More than 70% of aggregate sizes > 0.25 mm were stable in the 0-25 cm depth in all the profiles. Aggregated silt and clay was about 30% in the cattle grazing soils and 26% in the control. This development may be due to the shrinking and contracting behaviour of the soil rather than the residues from the cattle. Clay dispersion index (CDI) value of 0.3gg-1 and the negative values in potential structural enhancement index (PSEI) in the 0-25 cm and 25-50 cm soil indicate deleterious impact of cattle grazing on the soil structure. There was significant (P<0.01) positive correlation between ASI and MWD in Assang soils. Whereas increases in ASI lead to increases in MWD, the significant (P<0.01 positive correlation (r= 0.726) between CDI and OC in Assang soils implies that organic matter acted as disaggregating agent when not in close association with the soils particles. The exchangeable Ca, Mg and K were significantly high in the cattle grazing soils, evidencing the high chemical fertility of such soils. Intensive grazing by cattle promotes deformation of soil structure, especially under uncontrolled soil moisture content. Tillage within optimal moisture content will enhance the location of Ca, Mg, K and N for plant growth.
Key words: Structural stability, cattle grazing, heavy clay soil, organic carbon.
