Potassium and Sodium Interrelations in Growth and Mineral Content of Italian Ryegrass1

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Abstract
Growth and mineral content of Italian ryegrass were affected by K and Na treatments when studied by a nutrient solution technique. Potassium influenced plant growth more than did Na. Sodium substituted partly for K in top growth when K was low in the nutrient solution. Changes in the amount of K in solution affected leaf and tiller sizes more than numbers. Visual K deficiency symptoms were delayed and were less severe when Na was high in the solution.Potassium and Na concentrations in all plant parts were directly related to K and Na treatments. Potassium concentration was higher in old blades than in young blades when plants were K deficient, regardless of Na treatment. Sodium concentration, unlike K, generally decreased with increased blade age. Potassium and Na concentrations in the stem were high, compared to other plant parts.The youngest blade that was fully open and had a ligule, blade 1, was determined to be the best plant part to sample. It was necessary to determine Na in addition to K in blade 1 in order to diagnose the K status of the ryegrass adequately. The critical K concentration was 0.8% for blade 1 tissue that contained more than 2.4% Na, dry basis. The critical K concentration was 3.5%, however, for blade 1 tissue that contained less than 0.3% Na, dry basis.

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