1985 Volume 54 Issue 3 Pages 336-343
Potassium fertilizer experiments of spinach were carried out to clarify the effects of growing season and plant age on the critical K concentration expressed as dry weight or % tissue water.
The relationships between the dry weight of tops and K concentration of the youngest leaf were usually delineated by the second or the third degree polynomials.
At the sixth leaf stage, the critical K concentration of the youngest leaf ranged from 4.3 to 6.7% when expressed on a dry weight basis. When expressed on a tissue water basis, it was not variable with about 0.7%, except after plants had been chilled.
In early summer, the critical K concentration of the youngest leaf was kept constant at about 0.7% on a tissue water basis, but that on a dry weight basis decreased from the fifth to the seventh leaf stage.