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Synopsis Manganese concentration in soybean plants increased 200 ppm. after 15 minutes contact between plant surfaces and applied manganese sulfate solution. Manganese absorbed by the leaves and stems increased with increasing manganese concentration in the applied solution, and with an increase in plant temperature and the length of time the manganese remained in solution on the leaf surface. A portion of the accumulated manganese appears to be held by adsorption at the leaf surface.

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Nine methods of extracting manganese from 25 soils were studied and correlated with manganese absorbed by soybean plants. Two of the methods, extraction with 0.1N H3PO4 and 3N NH4H2PO4 for 1 hour at a 1:10 soil/solution ratio, were developed during the investigation. Of the nine methods investigated, extraction of soil manganese with NH4H2PO4, alcoholic hydroquinone, and H3PO4 yielded the highest correlation coefficients (0.856 to 0.899), had the smallest variances, and as a group were statistically different from extraction with NH4OAc, NaOAc, and total soil manganese as methods of estimating plant available manganese. The ammonium dihydrogen phosphate extraction method with the highest correlation coefficient (0.899) was statistically different from methods of extracting soil manganese with H2SO4, hydroquinone in NH4OAc, HNO3, NH4OAc, NaOAc, and total soil manganese. Results indicate that manganese deficiency in soybeans may be expected if the manganese extracted with ammonium dihydrogen phosphate or phosphoric acid is less than 40 pp2m. With alcoholic hydroquinone, manganese deficiency may be expected if the manganese extracted is less than 125 pp2m.