Physiology

Abstract

Plant growth was inhibited owing to excess or luxury consumption of nitrogen with relatively lower protein accumulation by continuous nitrate supply. However, nitrogen was the dominant nutrient, if the amount of nitrate supply was adequate. The uptake of cations, especially potassium, was dependent on that of nitrate. There was a close correlation between anions and cations uptake. Although the optimum ratio of sulfate ions to total anions was approximately 15%, the application at higher sulfate levels was effective for the control of plant growth. It seems that a nutrimental period corresponds with the developmental stage of plants. The requirement of phosphate ions was nearly the same as that of sulfate ions. However, phosphate promoted the functional transition from sink to source leaf at successive leaf position, whereas sulfate retarded such the transition. Phosphate or sulfate supply at higher levels inhibited the dry matter production in plants. From these results, the optimum ratio of nitrate:phosphate: Sulfate in nutrient solution was estimated to be 70:15:15% of total anions in chemical equivalent for vegetative growth.

Key words:

• Nitrogen status
• developmental stage
• optimal ratio of anions
• method of systematic variation