Effects of N, P and K fertilisers on trace element status of oil palm in Sumatra

Trials testing application of N, P, K and Mg fertilisers to oil palm have been carried out in different locations on mineral soils in both North and South Sumatra and their effect on the content of both major and minor elements has been monitored. This paper reports the effict of these major fertilisers on the trace element status of the palms. In all four of the trials on old palms in North Sumatra, urea fertiliser significantly reduced the leaf levels of both copper and zinc, in some cases below tentative critical levels. In addition superphosphate fertiliser significantly reduced leaf copper in all four of these trials whilst muriate of potash fertiliser significantly depressed leaf zinc in two trials. In contrast, N and P fertilisers had no effect on leaf trace element levels in five trials on younger palms in South Sumatra, but in four of the trials,K fertiliser significantly reduced leaf zinc. There were no consistent effects of N, P and K fertilisers on leaf levels of B, Mn or Fe. Changes in soil properties due to the fertiliser applications do not appear to explain these results. Furthermore the effects of fertilisers on leaf trace element levels were not generally seen in the rachis, suggesting that uptake of trace elements into the palms was not significantly affected. The reduction in leaf copper and zinc levels may therefore be due to a physiological effect of the fertiliser nutrients inside the palms influencing the transfer of these trace elements to the leaves. Leaf concentrations of other trace elements were not generally affected by fertilisers, indicating that the results for copper and zinc are not due toa"dilution"effect resulting from increased growth. In the trials on older palms in North Sumatra, yields have generally fallen with time and Ganoderma incidence has increased in treatments where trace elements have been depressed by the major fertilisers. It is concluded that continuous application of N, P and K fertilisers is likely to have an adverse effect on the trace element status of oil palms, which if not corrected may result in reduced yields and increased disease incidence.