| Sumario: | Solutions of calcium phosphate, potassium phosphate, calcium phosphate-acetic acid, calcium phosphate-calcium chloride, ammonium acetate, and sodium bicarbonate-acetic acid, and calcium chloride were tested as extractants for sulfur from 30 Costa Rican soils. Calcium chloride, ammonium acetate and sodium bicarbonate-acetic acid were discarded because of either removing small amounts of sulfur or problems in analizing the filtrate by turbidimetry. Of the four remaining extractants, the sulfur extracted by calcium phosphate and by potassium phosphate was best related to sulfur responses by sorghum in the greenhouse.
Estimated critical levels for the four methods were six ppm for calcium phosphate-acetic acid, eight ppm for calcium phosphate, six ppm for potassium phosphate and three ppm for calcium phosphate-calcium chloride.
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