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Quantity, Distribution, and Variability of Organic Matter and Nutrients in a Forest Podzol in New York¹

ABSTRACT

The organic matter under yellow birch-red spruce forest (Betula alleghaniensis Britton-Picea rubens Sarg.) growing on well-drained, outwash sands of the Adams series was sampled intensively on eight one-tenth acre plots in the Adirondack Mountains of New York. Under old, undisturbed stands the mean depth of the forest floor was 6.4 inches (16 cm) and the mean weight was 216,300 ± 8,800 (90% confidence interval) lb/acre (242 metric tons/hectare). There was approximately 175,000 lb/acre of organic matter in the forest floor and about 142,000 lb/acre in the upper three horizons of the mineral soil. The average bulk density of the forest floor was 0.14 g/cm³. A theoretical O horizon accumulation curve was drawn based on samples from plots having different ages of accumulation. These ages were inferred from ecological information and from evidence of fire history. The concentration of organic matter in the B2h horizon was positively correlated with age of the forest floor. The undisturbed forest floor contained approximately 2,850 lb/acre of nitrogen or about 43% of the estimated total in the nutrient cycle. It also contained approximately 150, 90, and 620 lb/acre of phosphorus, potassium, and calcium, respectively.

Coefficients of variation ranged from .33 to .67, determined on the basis of 96 sample weights from the forest floor of each plot. Approximately 50 samples were needed to reduce the standard errors to 10% of the mean weights. Similar variability was found in the thickness of mineral soil horizons. Horizon thicknesses measured from a single soil pit in a 0.1-acre plot were not reliable estimates of thicknesses when compared with those determined by taking 12 to 24 core samples spaced throughout the same plot.

¹ Contribution from the Department of Agronomy, Cornell University, Ithaca, N. Y. Agronomy Paper no. 663. Presented before Div. S-5 and S-7, Soil Science Society of America. Nov. 18, 1964 at Kansas City.

² Graduate Assistant in Agronomy and Pack Professor of Forest Soils, respectively.

Received for publication November 2, 1964. Accepted for publication March 23, 1965.