Seasonal variation in foliar composition of black walnut trees

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Abstract
Leaf samples were collected from upper and lower crown positions at 3 times during the 1971 and 1972 growing seasons for planted black walnut (J. nigra L.) trees on the Kaskaskia Experimental Forest in Hardin County, Illinois [USA]. The average dry weight of leaves was affected by crown position and time of year. Foliar concentrations of N, P, K, Ca and Mg were affected by season, but not by crown position. The content of all elements tested and the concentrations of Ca and Mg increased with season while concentrations of N, P and K decreased as the season progressed. Suggestions for sampling dates are given. [The detection of nutrient deficiencies by analyzing tree foliage requires a knowledge of the seasonal trends of the various foliar elements.].