Potassium Influx Characteristics of Corn Roots and Interaction with N, P, Ca, and Mg Influx

At K levels usually found in soil solution, K influx characteristics of plant roots can be described by Michaelis- Menten kinetics. When only part of the roots are supplied with K, plant uptake of K may be reduced, causing a reduction in K concentration in the plant and this, in turn, may also reduce plant growth. Knowledge of how K distribution in the root zone influences K uptake by the plant is important in developing efficient practices of K fertilization. The objective of this research was to determine the K influx characteristics of corn (Zea mays L.) roots and investigate how supplying only part of the roots with K influences both K influx and N, P, Ca, and Mg influx. Four split-root experiments were conducted in solution culture. Corn was grown from 7 to 17 days with varying proportions of the root system supplied with K. Reducing the proportion of roots in K reduced K uptake by the plant; however, the K influx of the K-supplied roots increased up to 2.6 times that of roots on plants where all roots were supplied with K. Presence or absence of K in the solution bathing the roots did not affect root growth in these experiments. Two additional experiments were conducted to produce plants having varying shoot K levels for use in measuring K. influx characteristics. Analysis of all six experiments showed an inverse curvilinear relation between %K in the shoot and maximum K influx into the root (R²= 0.74). Comparison of K influx by K-supplied-roots and roots originally in solution without K that were attached to the same shoot indicated the K level in the shoot had a greater effect on K influx than K level of the root. Magnesium influx increased as K concentration in the plant decreased. Magnesium influx was much greater on the K-absent side than on the K-present side of the split-root system. Nitrogen influx was greater on the K-present than on the K-absent side.