Track 2-11: Plant Nutrition and Nutrient Cycling

Description

Sustainable cultivated pasture production in the southern Cape region of South Africa requires management practices that will support soil quality (Swanepoel and Botha 2012). Soil organic carbon (Corg) sequestration is regarded as one of the most important ways to promote soil quality. Dairy farmers in the southern Cape attempt to increase Corg by following minimum-tillage practices. These irrigated dairy-pastures require high levels of nitrogen (N) to maintain highly productive pastures. Nitrogen fertilisers have be-come very expensive and severely strain profitability of these dairy-pastures. Forage legumes are frequently incorporated into the grass pastures to overcome economic and environmental problems associated with high levels of inorganic fertiliser application. Their capacity to fixate atmospheric N contributes greatly to nutritional value, palatability and subsequently profitability of pastures (Botha 2003). Since C and N are biophilic compounds, Corg may have a direct effect on the N-fixating legume plant or the Rhizobium population that infects its roots (Swanepoel et al. 2011).

The aim of this study was to determine the effects of Corg on white clover (Trifolium repens) biomass production and N-fixation by host-specific Rhizobium.

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Rhizobium-White Clover Symbiosis and Nitrogen Fixation along a Soil Organic Carbon Gradient

Sustainable cultivated pasture production in the southern Cape region of South Africa requires management practices that will support soil quality (Swanepoel and Botha 2012). Soil organic carbon (Corg) sequestration is regarded as one of the most important ways to promote soil quality. Dairy farmers in the southern Cape attempt to increase Corg by following minimum-tillage practices. These irrigated dairy-pastures require high levels of nitrogen (N) to maintain highly productive pastures. Nitrogen fertilisers have be-come very expensive and severely strain profitability of these dairy-pastures. Forage legumes are frequently incorporated into the grass pastures to overcome economic and environmental problems associated with high levels of inorganic fertiliser application. Their capacity to fixate atmospheric N contributes greatly to nutritional value, palatability and subsequently profitability of pastures (Botha 2003). Since C and N are biophilic compounds, Corg may have a direct effect on the N-fixating legume plant or the Rhizobium population that infects its roots (Swanepoel et al. 2011).

The aim of this study was to determine the effects of Corg on white clover (Trifolium repens) biomass production and N-fixation by host-specific Rhizobium.