Abstract

Lampung district is among the major cassava producers in Indonesia. The soils of the region are acidic, with very low cation exchange capacity and negligible organic matter content. Assuming that potassium (K) availability is a limiting factor for cassava cropping under the given conditions, the effects of K fertilizer at six seasonal doses (0, 30, 60, 90, 120, and 180 kg K₂O ha^-1) applied once (15 days after planting), and one treatment attributed to farmers’ practice, were examined at two locations, Sukadana and Rumbia. All K fertilizer treatments were combined with 135 kg N ha^-1 and 36 kg P₂O₅ ha^-1, except one treatment with 200 kg N ha^-1 and 60 kg P₂O₅ ha^-1. Urea (46% N), SP36 (36 kg P₂O₅), and KCl (60% K₂O) were used as the source of N, P, and K fertilizer, respectively. While K doses hardly affected soil properties at harvest, they had obvious correlative influences on plant growth, organ K contents, and tuber yields. An optimum dose of 60-90 kg K₂O ha^-1 seemed to satisfy cassava requirements in Sukadana, whereas the adequate dose in Rumbia was a bit higher. Nevertheless, some evidence indicates that the potential for K fertilization and other means to improve cassava production in this region is considerably higher. Measures, such as division of the seasonal K dose into many frequent applications, and supplementation of composted organic matter, in order to enhance soil fertility and cassava crop performance, are discussed.