Response of cassava, sunflower, and maize to potassium concentration in solution II. Potassium absorption and its relation to growth

Abstract

The absorption, distribution and utilization of potassium by 12 cultivars of cassava, and one cultivar each of sunflower and maize, grown over a wide range of constant solution potassium concentrations (0.5 to 8024 μM) are reported. Absorption rates by cassava were generally lower than for the other species at all potassium concentrations. At the lowest potassium concentrations giving maximal growth, the rate of absorption per unit root weight by cassava cultivars varied between 41 and 68 μmol/g fresh root/day, while the values for sunflower and maize were 104 and 68 μmol/g fresh root/day, respectively. Greater relative root size of cassava at all solution potassium concentrations and ability to increase the relative size of the root system at low potassium concentrations, partially offset the low rates of absorption per unit root weight. As the solution potassium concentration increased from 0.5 to 6 μM, the proportion of potassium in the roots and younger leaves of cassava decreased while the proportion in the older leaves and stems increased. At higher solution potassium concentrations the proportion of total plant potassium in the roots continued to decrease but there was little effect on the other plant parts. At all solution potassium concentrations cassava cultivars utilized potassium more efficiently than either sunflower or maize in the production of dry matter.