Potassium management effects on yield and quality of cassava varieties in tropical sandy soils

Potassium (K) fertilisation at planting time may not be sufficient to achieve high cassava yields. Experiments were conducted over two growing periods using sweet cassava (SC) variety IAC 576-70 and bitter cassava (BC) variety IAC 13 aiming to evaluate the effects of K fertilisation rate (0-150 kg K/ha) and timing of application (one, two, or three) on leaf K concentration, yield components, and storage-root and starch yields. The SC and BC varieties were grown in a randomized block design in a 3 x 4 + 1 factorial scheme with four replications during growing periods of 10 and 20 months respectively. For SC, split application of K at planting plus 3 months after planting (MP) or at planting plus 1.5 and 3 MP was more effective at increasing the marketable root yield, with greater rainfall at the beginning of the growing period. Split application of K at planting plus 3 MP also reduced the cooking time and cooked root firmness. For BC, split application of K at planting plus 12 MP more effectively increased the storage-root and starch yields; however, root yield response to K fertilisation in the second growing period, with greater rain intensity during the initial crop stages, was greater than in the first growing period. In K-deficient soils, the optimal K application rate for SC marketable root yield varied from 79 to 111 kg/ha when K was applied after 1.5 MP, and linear responses to K application rate occurred when K was applied earlier. For BC, the optimal K application rate varied from 75 to 92 kg K/ha. Our data suggest that K application times should be different for cassava varieties with short and long growing periods.