During their first growing season, eastern cottonwood (Populus deltoides Bartr.) planted at a 3 by 3 m spacing on a slackwater clay soil (Vertic Haplaquept) in western Mississippi produced 3,680 kg/ha of dry matter. Of this, 900 kg/ha was in leaves, 700 in branches, 820 in stems, and 1,260 in roots. Seventy-six percent of the aboveground biomass was accumulated during August and September. At the end of September, just prior to leaf fall, the trees contained 43.5 kg/ha of N, 4.7 kg P, 34.7 kg K, 36.5 kg Ca, and 6.4 kg Mg. From 62 to 79% of these elements was accumulated in August and September.
Foliar N and P concentrations peaked in early summer, then steadily decreased until leaf fall in November. Branch and stem N and P decreased from a maximum in early summer to a low in September, then increased during October and November. Seasonal patterns of Ca and Mg were similar to those of N and P, except that foliar concentrations steadily increased throughout the summer to a maximum at time of leaf fall. Trends in foliar K were similar to those of N and P; however, K concentrations in branches and stems declined through the summer to a low at time of leaf fall.
Of the total quantity of N, P, K, Ca, and Mg in the foliage in September, 26% of the N, 33% of the P, 28% of the K, 62% of the Ca, and 51% of the Mg fell with abscised leaves in November. Sixty-one percent of the foliar N and 53% of the foliar P were translocated to other tissue prior to leaf fall. Potassium, calcium, and magnesium were not involved in internal nutrient cycles since they were not translocated and retained in support tissue. A large portion of the foliar K was apparently leached or lost through root exudation or other means.