SOIL TESTING FOR PHOSPHORUS IN SOME NIGERIAN SOILS

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Abstract
Seven chemical extractants for determining available soil phosphorus have been compared with respect to their effectiveness in extracting phosphorus and the precision of the extracted phosphorus in predicting the phosphorus fertility of the soils. Strong alkali extraction using 0.1 N sodium hydroxide extracted the most phosphorus but was the least precise in predicting yields (r = 0.58). Inclusion of organic phosphorus in the sodium hydroxide extract reduced the precision further (r = 0.56). Extraction with dilute acids and an anion exchange resin gave lowest values for available phosphorus but resin extraction was superior to dilute acid extraction in predicting percentage yields, with a correlation coefficient of 0.72 for resin extraction compared with 0.60 and 0.68, respectively, for 0.002 N sulfuric acid and 3 percent acetic acid. Extraction with 0.5 M sodium bicarbonate and 0.03 N ammonium fluoride plus 0.025 N hydrochloric acid were equally precise in predicting percentage yields with correlation coefficients of 0.67 and 0.68, respectively. The phosphorus extracted with 0.03 N ammonium fluoride plus 0.1 N hydrochloric acid gave the highest correlation with percentage yield (r = 0.74). This method, being additionally simple, quick, and effective ir extracting phosphorus, has been recommended for the routine soil testing for phosphorus in the acid soils of southeastern Nigeria. © Williams & Wilkins 1977. All Rights Reserved.

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