The Impact of Lime and Gypsum on Sugarcane Yields and Soil Acidity in the South African Sugar Industry

The yield responses of sugarcane to lime and gypsum at two sites in the KwaZulu-Natal Midlands of South Africa are presented and discussed. At Dalton, on a Magwa form soil with an initial aluminium saturation index (ASI) of >80%, over a plant and four ratoon crops variety N12 gave no significant response to dolomitic lime. By contrast, variety N16 gave consistent yield responses to lime at rates of up to 10 t/ha, and also to applications of 5 t/ha lime plus 5 t/ha gypsum, which gave the highest overall yield. At Paddock, on a Nomanci form soil with an initial ASI of about 80%, N16 gave consistent responses to dolomitic lime applied at 7 t/ha in the first to fifth ratoon crops, while N12 responded similarly from the third ratoon onwards. NCo376 gave yield responses to rates of 14 t/ha from the second ratoon onwards. The results confirmed the revised Fertiliser Advisory Service method of recommending lime to ensure that yields are not limited by soil acidity. In addition, there appears to be merit in applying gypsum as well as lime to acid soils. The implications for future research work on liming are discussed.