The Distribution of Mg, P and K in the Split Roots of Subterranean Clover

The aim of these experiments was to determine whether uninhibited root growth is possible in a soil lacking Mg, provided that the plant is adequately supplied with Mg from another region within the soil. Two experiments were undertaken using split root systems in free-draining sand or gravel irrigated daily with nutrient solution. Magnesium supply to one half of the root system was varied and root growth in the deficient part of the system was measured. Magnesium redistribution was compared to that of calcium, phosphorus and potassium. Magnesium content of the roots grown in the compartment with no Mg supply increased, but only when the shoots had an adequate to luxury Mg status. Even under these conditions root growth was inhibited compared to roots with an adequate external supply in both compartments. Similarly potassium was transferred to the roots with no external supply, but root growth was retarded in this compartment. Roots proliferated in the compartment supplied with phosphate and did so at the expense of growth in the non-supply compartment. The shoots had a barely adequate phosphorus status and there was no transfer of phosphorus to the root with no external supply.