High Soil Test Phosphorus Increases Soybean Yields
 A 55-bu/A soybean crop takes up 53 lb P2O5/A. Each bushel of soybeans removes 0.80 lb P2O5. Without phosphorus (P) fertilization, soil test levels will decline and yields will suffer. To increase yields, farmers should apply enough phosphate fertilizer to replace harvested P2O5 and also raise soil test P levels over a four- to eight-year period to optimum levels. Optimum soil test P levels will vary with the soil texture and clay chemistry. For most soils and cropping systems, the following table on relative soybean yields can be used as an approximate guide in managing soil test P to raise soybean yields.
Soil
Test P
(lb/A) | Mehlich 3 extractant | Bray-Kurtz P-1 extractant |
AR | KY | MO | IA | IL |
---------------- Relative soybean yield, percent ---------------- |
5 | --- | 46 | 21 | 20 | 42 |
10 | --- | 63 | 40 | 38 | 55 |
20 | --- | 78 | 69 | 70 | 81 |
30 | 72 | 86 | 89 | 90 | 95 |
40 | 90 | 92 | 99 | 96 | 98 |
50 | 95 | 95 | 100 | 98 | 99 |
60 | 100 | 97 | 100 | 100 | 100 |
70 | 100 | 99 | 100 | 100 | 100 |
For more details, please refer to the May 2000 Midsouth News and Views article - Raise Soybean Yields and Profit Potential with Phosphorus and Potassium Fertilization.
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