The Chemical Estimation of Plant Available Soil Manganese

Nine methods of extracting manganese from 25 soils were studied and correlated with manganese absorbed by soybean plants. Two of the methods, extraction with 0.1 N H 3 PO 4 and 3 N NH 4 H 2 PO 4 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 NH 4 H 2 PO 4 , alcoholic hydroquinone, and H 3 PO 4 yielded the highest correlation coefficients (0.856 to 0.899), had the smallest variances, and as a group were statistically different from extraction with NH 4 OAc, 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 H 2 SO 4 , hydroquinone in NH 4 OAc, HNO 3 , NH 4 OAc, 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.