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University of KwaZulu-Natal (2002)

An investigation of factors contributing to soil degradation under dairy farming in the Tsitsikamma

Milne, Ryan McKinlay.

Titre : An investigation of factors contributing to soil degradation under dairy farming in the Tsitsikamma.

Auteur : Milne, Ryan McKinlay.

Université de soutenance : University of KwaZulu-Natal

Grade : MASTEROF SCIENCE (AGRICULTURE) in Soil Science 2002

Résumé partiel
Pasture-based dairy farming is the major land use in the Tsitsikamma region of the Eastern Cape. Permanent kikuyu grass (Pennisetum clandestinum) dominates pastures in the region. Kikuyu pastures do not, however, provide adequate year-round quality feed for dairy cows. This has led to the use of annually sown pastures with perennial ryegrass (Lolium perenne) to provide winter forage. Soil degradation under this management has, however, become recognised as a major limitation. Soil quality and degradation under annual and permanent pasture in the region were evaluated in three separate studies. These were (i) an investigation of the extent of loss of soil organic matter and related soil microbial properties and aggregate stability under annual pastures, (ii) a comparison of soil physical properties under annual and permanent pastures and (iii) a survey of the nutrient status of soils and pasture herbage in the region. In the first study, four commercial dairy farms, situated on sites which represented the three main soil groups in the region were sampled, were taken from under permanent kikuyu pastures, annual ryegrass pastures and undisturbed native vegetation nearby. In comparison with undisturbed, native vegetation, soils under both annually cultivated and permanent pasture had gained soil organic matter on the sandy, low rainfall eastern end of the Tsitsikamma. By contrast, at the higher rainfall, finer-textured, western end, where the native vegetation consists of coastal forest, there was a loss of soil organic matter under both types of pasture. Despite this, soil organic C content was lower under annual ryegrass than permanent kikuyu pasture at all the sites reflecting the degrading effect of annual cultivation on soil organic matter. As a consequence, labile, K(2)S0(4) - extractable C, microbial biomass C, basal respiration, arginine ammonification, flourescein diacetate hydrolysis rates and aggregate stability were all less under annual ryegrass than permanent kikuyu pastures at all the sites.

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