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Response of Slash Pine to Colloidal Phosphate Fertilization¹

ABSTRACT

Single applications of 0.5 to 2 tons of colloidal phosphate per acre, made at time of planting of slash pine (Pinus elliottii Engelm.), resulted in significant increases in tree growth over a 15-year period. Results from replicated treatments, applied in 1945 near Gainesville and Welaka, Florida, indicate the commercial feasibility of fertilizing slash pine on acid "flatwood" soils.

Neither tree survival nor wood density were significantly influenced by treatment. Average dbh and volume per merchantable trees were significantly greater in fertilized plots than in controls at both locations. The best treatment, considering treatment costs and timber value at the end of 15 years, was 0.5 ton of colloidal phosphate per acre applied in alternate 4-foot strips and disked. Cordwood volumes in this treatment averaged 45% greater than in the untreated controls. Disking of the soil following the application of the phosphate material increased yields by about 3 cords per acre over yields obtained from phosphate alone.

Extractable soil phosphorus and phosphorus content of needles from treated plots were higher than from control plots in the Gainesville experiment, but not in the Welaka experiment.

¹ Contribution from the Florida Agr. Exp. Sta., Gainesville, as Journal Series, No. 1222. Presented before Div. V-A, Soil Science Society of America, Dec. 5, 1960, at Chicago, Ill.

² Soils Technologist and Forester, respectively.

Received for publication December 19, 1960. Accepted for publication May 29, 1961.