The Application of Fertilisers to Pines in Southern Africa
Abstract
SYNOPSIS Phosphate is the major limiting element for tree growth in Southern Africa. Once phosphate requirements have been met responses to N and K may also occur. N and K applied without P will cause a growth reduction. Manganese deficiency in some areas of the Southern Cape is the only example of a trace element deficiency causing crop failure in South Africa. With the exception of P. pinaster which has not responded consistently, all the commercial pines have responded to fertiliser application. Response to fertiliser application at planting appears likely to last to the first thinning and to be economically viable. Responses in unthinned stands, unless widely spaced or clearfelled at an early age, are less likely to last to clearfelling. The application of fertiliser to older crops at time of thinning holds good promise of an economic return, but the stands must be adequately released to ensure a growth response. Research to date indicates that 10 to 25 kg P per hectare as superphosphate or 2:3:2(22) should be applied at planting. The method of application should be spot placement in a depression some 200 mm from the tree. A further application of 50 to 90 kg P per hectare at first thinning will ensure maximum growth. This fertiliser should be evenly broadcast throughout the stand. The use of fertilisers in Southern African forestry will expand rapidly in the eighties but more work is needed to refine the prescriptions and broaden the data base which supports them.