Foliar macronutrients (N, P, K, Ca and Mg ) in lime (Tilia spp). II. Seasonal variation

Mid summer leaf samples collected from 24 lime trees over a four year period (1975 to 1978) were analysed for macronutrient (N, P, K, Ca and Mg) concentration. Correlation analysis of the results showed that the concentrations of N and of P in the leaves in different years were not closely related. However, the concentrations of K, Ca and Mg were very highly correlated with the concentrations found in previous years. Foliar sampling and nutrient analysis of 30 Common limes (Tilia × europaea) throughout the summers of 1977 and 1978 confirmed that for K, Ca and Mg there was good correlation between the concentrations found at given dates in successive seasons. There was good agreement between the patterns of variation through the two seasons exhibited by each of the five macronutrients measured. The concentrations of N, P and K were highest at the earliest date of sampling in late May when leaf expansion had just been completed. All three nutrients then showed a rapid drop in concentration the rate of which decreased by mid-June. The concentrations then continued to decrease at a slower rate until the lowest levels were reached just prior to leaf fall at the end of October. There was some evidence of résorption of N and K by the tree during September and October, when the rate of reduction in their foliar concentrations increased sharply. This could not be explained as a dilution effect because all leaf growth had stopped and the leaves had begun to change colour by that time. Ca and Mg concentrations were lowest at the beginning of the season when sampling was first done. The concentration of Ca continued to rise steadily throughout the season reaching its highest level just before leaf abscission. The concentration of Mg increased rapidly through June and then fluctuated for the rest of the summer, although it tended to decrease towards the end of the season.