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Radioactive Studies with P³² in Tropical Soils and Crops of Puerto Rico¹

ABSTRACT

Six experiments—three with sugarcane, one with pineapples, and two with coffee—were completed with P³² to determine what percentage of the phosphorus was taken by the crop from the fertilizer and from the soil respectively. Five different methods of applying the fertilizer to coffee trees were also studied. Superphosphate tagged with P³² was used. The contents of total P and P³² in the crop leaves served as an index for this work.

The data and results obtained in the sixth experiment, the second with coffee, are presented here. A second objective of the experiment was to determine if the leguminous trees, that serve as shade to the coffee trees, absorb part of the phosphorus added as a fertilizer.

The results obtained indicate that coffee trees absorbed a highly significantly greater percentage of the phosphorus from the fertilizer when it was broadcast over the whole or over a 2-foot wide outer segment of the canopy area than when it was applied in bands, in holes, or over the terrace.

The results indicate also that the leguminous shade trees absorb part of the phosphorus applied to the coffee trees.

¹ Rec. for publication Sept. 10, 1954.

² Soil Chemist, Head of Soils Department; Associate Chemist in Charge Central Analytical Laboratory, and Assistant Chemist, Soils Department, respectively, Agricultural Experiment Station, University of Puerto Rico, Rio Piedras, Puerto Rico.