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Evaluation of Soil Testing Methods for Predicting Growth and Response of Pinus elliottii to Phosphorus Fertilization¹

ABSTRACT

Soil tests were evaluated as methods for predicting height growth or increased height growth due to P fertilization of Pinus elliottii var. elliottii Engelm. on acid Coastal Plain soils. Growth and response parameters were obtained from field and greenhouse trials fertilized at time of planting with N and P. Field trials were measured 1, 3, and 5 years after planting and the greenhouse trial, which involved unfertilized soils collected from the field trials, was measured 1 and 2 years after planting.

The amounts of P extracted by H₂O or NH₄OAc (pH 4.8) were the most closely correlated with height growth and response to P fertilization after 1 year of growth in both the greenhouse and field. The effectiveness of these methods declined after longer growth periods. Methods which extracted larger amounts of P—0.5M NaHCO₃; 0.05N HCl + 0.025N H₂SO₄; 0.03N NH₄F + 0.025N HCl—were more effective predictors of response to P fertilization over growth periods of 3 and 5 years in the field. Phosphorus extracted by 0.03N NH₄F + 0.025N HCl was the most closely correlated with response recorded after 5 years (r² = 0.778).

Concentrations of P in the tops of greenhouse-grown pine seedlings after both 1 and 2 years growth were most closely related to P removed by the stronger extractants. The r² values for the relationships between soil test values and both concentrations of P in seedling tops after 2 years and in foliage of field trees at age 4 were almost identical.

¹ Contribution from the Florida Agr. Exp. Sta., Gainesville, as Journal Series no. S474. Financial assistance from the National Research Advisory Council of New Zealand and the Cooperative Research in Forest Fertilization (CRIFF) program is acknowledged.

² Graduate Assistant and Professor of Forest Soils, Univ. of Florida, Gainesville, respectively. Senior author is also Scientist, Forest Research Inst., Rotorua, New Zealand.

Received for publication July 7, 1974. Accepted for publication September 12, 1974.