Copper Toxicity in Oil Palms on Peat and Its Effect on Palm Growth and FFB Production

Abstract

This paper documents a case of copper toxicity observed on young mature palms in a fertiliser trial evaluating the comparative efficacy of applying three micro nutrients (copper, zinc, iron) via four application techniques (soil, foliar spray, root infusion and trunk injection) in peat soil. Oil palms were more sensitive to copper than either zinc or iron, as toxicity was only induced by the former although the latter two micro-nutrients were applied at much higher rates. With copper, applying a dosage as low as only 3.0 g CuSO4 per palm via root infusion or trunk injection was more toxic than applying the same fertiliser to peat soil (soil application) at rates 166 times higher. Copper toxicity, manifested as scorching or “burn” of lower and middle level fronds, had no negative effect on palm growth, but significantly lowered fresh fruit bunch (FFB) production by as much as 3.0 tonnes per hectare per annum. A drop in yield was consistently recorded 9 to 10 months after each annual application of copper and was caused by a significant reduction in the number of bunches harvested. The latter was attributed to an increase in the rate of female inflorescence abortion, four to five months prior to anthesis or 9 to 10 months before harvest. Lowering of the inflorescence sex-ratio could be another contributing factor. Keywords: Copper, micro-nutrients, oil palm, peat, toxicity.