Two experiments to investigate the micronutrient requirements of cassava (cv Black Twig) on Malaysian peat soil are described. Cu was found to be the only essential micronutrient and Mn, Zn, Fe, Mo and B were not needed. Fertilizing with 20 kg/ha of copper sulphate approximately tripled tuber dry matter, and starch and Cu uptake, but applying 10 kg/ha of copper sulphate gave the same results. Each crop of cassava absorbed only about 2% of the applied Cu, giving a leaf Cu content of about 14 ppm compared with about 7 ppm in Cu-deficient plants. Cu deficiency symptoms were invariably observed in Cu-deficient plots and these are also described.
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