Seasonal and year-to-year trends of leaf K, Ca, and Mg content in healthy and Mg-deficient Ralls trees were studied in order to obtain more information about the factors which affect the occurrence of Mg-deficiency.
Seasonal samples of mid-shoot leaves (without petioles) were taken with 10 day intervals during the period of 1958-1961, from the same trees of two blocks (Block A: Mg-deficient, Block C: healthy) of experimental field, details of which were described in a previous paper(16).
Changes of leaf K, Ca, and Mg content from mid-June to early-November indicated that decrease of K, and increase of Ca and total cation (K+Ca +Mg as me) content showed almost linear pattern throughout the season, whereas slow increase at the beginning and slow decrease at the end of the season was exhibited in the case of Mg. Considerable variations in leaf cation content were observed within each season, and variation coefficient of leaf Ca was the greatest, and that of K was greater than that of Mg and total cation. The period between 80-90 days after full bloom would be the time when the least change of Mg was occuring in the leaves, and the period between 110-130 days would be preferable to attain the maximum difference in leaf Mg content between high-and low-Mg trees.
Yearly leaf samples were collected at about 85 days after full bloom during the period of 1958-1966, from the same trees (except for Block A since 1964) of the two blocks.
Within-season variations in leaf K, Ca, and Mg content were greater than that of between-season, except that Mg in low-Mg trees.
The observed variations in the severity of Mg-deficiency from year to year seemed to be associated with variations in leaf Mg content of low-Mg trees. It was observed that the highest Mg content was found in 1961, when the K content was at its lowest and the fruit yield was at its highest, and that a high Ca content was found in 1963, when the lowest Mg and a high K content was found.
No significant correlation was found between leaf cation content of each year and yearly climatic conditions, and also between leaf cation content and fruit yields, however, some significant positive correlations were obtained between mean air temperature of each year and Ca content of leaves. The result suggests that variation of air temperature during the growing season is responsible to some of the between-season differences in leaf cation content observed in the present work.
There were negative correlations between leaf Ca and K content, and also between Ca and Mg content of leaves from low-Mg trees when nutrient content was expressed as me-percentages of total cation.
