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Nelson Mandela University (2020)

Impacts of cattle grazing pressure on vegetation and soil characteristics in an arid grassland of South Africa

Botha, Gert Stephanus

Titre : Impacts of cattle grazing pressure on vegetation and soil characteristics in an arid grassland of South Africa

Auteur : Botha, Gert Stephanus

Université de soutenance : Nelson Mandela University

Grade : Magister Scientiae 2020

Résumé
Natural rangelands are often degraded due to the implementation of incorrect grazing systems. One potential solution is the use of short duration, high intensity grazing. The impacts of this grazing system on, inter alia, vegetation and soil properties have not yet been comprehensively tested within the arid rangelands of South Africa. This study aimed to determine the impacts of grazing intensity on vegetation composition, forage quantity and quality, and soil compaction, soil water infiltration rates and soil chemical properties in an arid grassland in South Africa. The following three grazing treatments were compared : no grazing (NG), low intensity grazing (LIG) and high intensity grazing (HIG). A total of 18 plots (six replicates per treatment) were grazed with Bonsmara cattle. Each plot, 4 ha in size, was surveyed pre-grazing, directly after grazing, and again three, six and 12 months post-grazing. The results indicated that different grazing intensities did not affect grass diversity and the veld condition a year after grazing. Phytomass was influenced by grazing intensity, with no grazing having the highest phytomass throughout the study period. Soil compaction differed among seasons but not among treatments, with summer surveys recording the lowest soil compaction rates. The soil water infiltration rates did not differ between the three different treatments, indicating that grazing intensity did not affect infiltration rates. However, grazing did seem to improve soil nutrient levels when compared to NG. The grazed treatments had higher NH4+, K+, and organic carbon than the NG treatment. Nevertheless, there was no significant difference in nutrients levels when comparing the LIG system to the HIG system. When comparing the soil nutrients levels within a treatment over time, only the HIG treatment showed an increase in soil nutrient levels (Mg2+) over time, whereas the LIG and NG treatments showed no changed throughout the study period. Generally, the study results indicated that in the short term there was no advantage to using higher grazing intensity, although the presence of grazing (as opposed to no grazing) is advantageous to arid grassland functioning.

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