EVALUATION OF PUTRESCINE AS A BIOCHEMICAL INDICATOR OF THE POTASSIUM REQUIREMENTS OF LUCERNE

SUMMARYThe diamine putrescine was found to be a sensitive indicator of potassium requirements of lucerne. There was an inverse relationship between the concentration of putrescine and that of potassium and the lowest concentrations of putrescine occurred only in plants which produced in excess of 90 % of the maximum dry matter yield. Using the point where the concentration of putrescine reached a minimum as an indication of healthy growth, it was established that a potassium concentration of 3 % of the dry matter of the leaves would be required for optimum dry matter production of lucerne at the early bloom stage of development; the corresponding value in the stem was estimated to be 5 % of the dry matter. While a low supply of magnesium enhanced the accumulation of putrescine in potassium deficient plants, potassium was shown to be the major factor influencing the concentration of putrescine. The advantages of using the concentration of putrescine as a basis for estimating the potassium requirements of lucerne are discussed in relation to the difficulties encountered with the conventional critical levels concept.