Response of cassava (Manihot esculenta Crantz) to calcium and potassium in a humid tropical upland loamy sand soil

Calcium (Ca) and potassium (K) are essential nutrients for plant growth but the antagonistic effect between these nutrients may reduce crop yield. A two–year field trial was carried out in a loamy sand soil to evaluate cassava response to Ca (0, 50, 100, and 200 kg ha⁻¹, as ground limestone, GL) and K (0, 50, 100, and 200 kg K₂O ha⁻¹, as potassium chloride, KCl). Calcium addition, especially 200 kg Ca ha⁻¹, adversely affected soil K availability with more pronounced on water–soluble K than on exchangeable and non–exchangeable K from day–7 onwards. Both Ca and K had no antagonistic impact on cassava. However, growth and yield responded positively to K more promptly than to Ca. Combined rates, except 100 kg Ca ha⁻¹ with no K fertilizer, significantly increased fresh tuber yield by 7.6–41.1 % over the control. To gain the highest fresh tuber yield by adding 200 kg Ca ha⁻¹, 200 kg K₂O ha⁻¹ must be implemented. This light–textured soil was physically preferable for cassava tuberization, and the optimum yield can be achieved by proper Ca and K fertilization.