Potassium efficiency of 10 potato cultivars as related to their capability to use nonexchangeable soil potassium by chemical mobilization

Ten potato cultivars were grown in low potassium soil with and without potassium (K) in a pot experiment to test their K efficiency. Two harvests (29 and 83 days after planting) were taken to obtain final dry matter (shoot + tubers) accumulation (DMA) rates of shoot and root growth and K uptake rate per unit root (K influx). Under K deficiency, DMA of different cultivars varied by a factor of more than 2. Based on absolute DMA without K, the cultivars, Linda, Oktan, Ponto, and Maas were more K efficient than Quarta and Belana. Results show that with the same root length, more K efficient cv. Oktan had higher relative shoot growth rate and produced more DMA than less K efficient cv. Quarta in the absence of K by taking up more K per plant from soil and maintaining higher shoot K concentration. The more K efficient cv. Oktan could take up more K per plant due to its higher K influx, and its higher influx was because of its capacity to use higher nonexchangeable soil K. The DMA, K uptake, and K influx in 10 cultivars were more correlated to the quantity of nonexchangeable K depleted (r = 0.850, 0.98 1, and 0.608) than to that of exchangeable K (r = 0.284, 0.363, and 0.315, respectively). Stepwise regression analysis indicated that capacity to use nonexchangeable K is the main factor controlling K efficiency of different cultivars followed by root length to DMA ratio and K influx.