Potassium‐Magnesium Interactions Affecting Nutrient Uptake by Wheat Forage

Authors:
  • TOTsutomu Ohno
    Tsutomu Ohno
  • DGD. L. Grunes
    D. L. Grunes
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Abstract
An important factor in the etiology of grass tetany is the role of K in suppressing the Mg concentration of the forage. A solution culture experiment was conducted to investigate K‐Mg interactions in winter wheat forage ( Triticum aestivium L. ‘Centurk’). The treatments were a factorial combination of K at 0.1, 1.0, and 6.0 m M and Mg at 0.1, 0.5, 1.5, and 4.5 m M . The plants showed a growth response to nutrient solution K levels, but not to nutrient solution Mg levels. Increasing K supply depressed Mg shoot concentrations, but not Mg root concentrations. Influx rate calculations showed that the external solution concentration of K did not affect the Mg influx rate. This implies that the antagonistic K‐Mg interaction mechanism is seated in the translocation step from the root to the shoot. The Mg concentration in the nutrient solution did not affect the shoot or root concentration of K, or the K influx rate. However, increasing the Mg level decreased both the Ca concentration in the shoots and the Ca influx rates. A soil culture study was conducted to investigate the influence of the nutrient transport mechanism on the chemical composition of plants. Plants grown at 30% relative humidity had higher K/(K + Mg) ratios than plants grown at 90% humidity. This was caused partly by the greater quantities of K delivered to the root‐soil interface by mass flow, owing to greater transpiration at the lower humidity level. Calculations showed that K depletion zones formed around the root‐soil interface at the lower K fertilization levels. Thus, the K + uptake was regulated by nutrient diffusion from the bulk soil to the root surface.

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