Nutritional requirements and interactions of Khaya senegalensis on tropical red and yellow earths

Abstract Factorial experiments with the treatments N, P, K, and a minor and trace element treatment (T) were carried out with African mahogany (Khaya senegalensis) on two soils in the glasshouse. The best growth was on the N+P+T treatments; if any one element was omitted growth was greatly reduced. A second experiment showed that of the elements in the T treatment, S gave a growth response while Ca, Mg, and B did not. (Zn, Cu and Mo were not tested but tip die‐back and chlorotic leaves suggested that Zn was required.) Applications of N, P, K, and S increased the corresponding foliar levels but in the treatments which showed the best growth response the foliar levels were lower than those when one of the elements was omitted. It is suggested that foliar nutrient levels higher than those occurring in healthy trees may indicate that another nutrient is limiting growth. For instance foliar levels greater than about 0.12% P, 0.7% K and 0.13% S may indicate that the supply of P, K and S respectively is adequate...