EFFECTS OF POTASSIUM DEFICIENCY ON SOME ORGANIC CONSTITUENTS IN PLANTS

The effects are described of nitrogen and potassium fertilizers on growth and the contents of soluble carbohydrates, free amino acids and amins in Italian ryegrass grown in K-deficient soil in the greenhouse. All combinations were tested of 40,80 and 160 ppm of N (applied as ammonium nitrate and 0, 60, 120, and 240 ppm of K (applied as potassium chloride) in air-dry soil.

Adequate potassium was needed to give maximum amounts of sugars and fructosan in the tops and stubble. In the grass grown without added K, increasing N-fertiliser increased the contents of ammonium-N, nitrate-N, free amino acids, glutamine, asparagine and amines (agmatine and putrescine) and decreased the protein-N content. When N-fertiliser was balanced with K-fertilizer-, all these soluble N-fractions decreased and protein-N increased. As glutamine and asparagine were predominant compounds most affected by potassium, estimating these two amides indicates the state of nitrogen metabolis in the plants. The amine content of plants provides a more sensitive indication of potassium deficiency than does the potassium content. Since the determination of agmatine is much easier than of putrescin agmatine content is proposed as an indicator of the potassium status of plants.