Target Soil pH

The target soil pH for soybean production on mineral soils is 6.3; which is slightly higher than that for corn (6.0), but lower than the target pH for forage legumes (6.5-6.8). On organic soils, the target pH is 5.6. If the current field average soil pH is greater than 0.2 units below the target, lime should be applied. It is recommended to manage soil pH based on the highest target pH-crop in the crop rotation. See A2809’s Soil pH and Lime Requirements section for more information on pH, buffer pH, and lime recommendations.

Nitrogen

Research in Wisconsin suggests that nitrogen applications are not necessary for soybean production.

Phosphorus and Potassium

Soybean is classified as demand level 1 for phosphorus (P) and potassium (K) (see Appendix B for more information regarding demand levels and Wisconsin’s P/K management approach). Soil test P (STP) and K (STK) should be managed for the highest demand level crop in the rotation. Soil test interpretation for demand level 1 crops, soybean P₂O₅ and K₂O removal coefficients, and P₂O₅ and K₂O fertilizer rate guidelines are provided below.

Summary

Optimum STP is 17-24 and 26-33ppm, while optimum STK is 121-150 and 66-90ppm, for loamy and sandy soils, respectively. Nutrient removal estimates, in combination with realistic yield goals, are used in developing application rate guidelines.

Soils testing in the optimum range results in application rates that match expected crop removal to maintain current soil test levels.

Soils testing low or very low results in application rates that exceed crop removal to build up STP/STK levels into the optimum range over a 4-to-8-year period.

Conversely, soils testing above optimum (high for P and K; very high for K) result in application rates below crop removal to slowly draw soil test levels down into the optimum range.

Applications of P/K are not recommended when soil test levels are in the excessively high category due to very low probabilities of profitable crop response to additional nutrient.

Soil Test Interpretation Categories

Note: If the field where soybeans are being produced will be irrigated, use the STP/STK interpretation ranges for demand level 2 crops

Soybean P₂O₅ and K₂O Removal Rates

Phosphorus (P₂O₅) Application Rate Recommendations for Wisconsin Soybeans

Potassium (K₂O) Application Rate Recommendations for Wisconsin Soybeans

Potassium (K₂O) Application Rate Recommendations for Wisconsin Soybeans

In addition to Tables 4 and 5 above, P₂O₅ and K₂O rate recommendation equations are also provided here. Simply select the correct soil test interpretation category and insert a realistic soybean grain yield goal into the P₂O₅ or K₂O equation to determine a specific application rate recommendation (units = lb of nutrient per acre).  

Secondary and Micronutrient Recommendations for Wisconsin Soybeans

Nutrient application guidelines for secondary and micro-nutrients to soybean are generally limited to nutrients where soybean have a medium or high relative demand and when soil and/or plant analysis suggest a deficiency may be present. From research trials in the state, profitable soybean yield responses to added secondary and micronutrients are rare.

Secondary Nutrients

Micronutrients

Manganese Fertilizer Recommendations for Wisconsin Soybeans

Soybean has a high relative manganese (Mn) requirement. Generally, soybean Mn deficiencies occur most commonly on calcareous muck soils; they are rarely observed in any other field setting. If a Mn deficiency is suspected, and soil test Mn is in the “low” category, apply 5 lb Mn/ac in the row (sulfate or ammonium forms will enhance availability); chelate forms are not effective when soil applied. Foliar applications of 1.25 or 0.2 lb Mn/ac of sulfate or chelate forms, respectively, are also effective. Research has shown that foliar applications of Mn to soybean fields that were not exhibiting Mn deficiency symptoms and had more than 30 ppm Mn in a tissue sample taken at the R1 growth stage did not result in yield increases 

Zinc Fertilizer Recommendations for Wisconsin Soybeans

Soybean has a medium relative zinc (Zn) requirement. Observed Zn deficiencies in soybean are rare in Wisconsin. If soil test Zn is low, and if plant analysis confirms a suspected Zn deficiency, Zn should be applied to soybean. Band (2-4 lb/ac; 0.5-1.0 lb/ac if chelated form) or broadcast (4-8 lb/ac; 1-2 lb/ac if chelated form) applications are effective. Foliar applications of 1.0 lb/ac of zinc sulfate or 0.15 lb/ac of zinc chelate may also be effective. 

Boron and Copper Fertilizer Recommendations for Wisconsin Soybeans

Soybeans have a low relative boron (B) and copper (Cu) requirement, and observed deficiencies are uncommon. Boron deficiencies are likely to be more prominent on sandy soils due to lower natural B content and lower capacity to hold B than loamy soils. If soil test B is low, and plant analysis confirms a suspected B deficiency, soybean may respond to added B. Copper deficiency is generally only suspected on very acid soils, particularly mucks. For soybean, Cu application guidelines are only provided for organic soils, where band application rates of 2 lb Cu/ac (inorganic forms) or 0.3 lb Cu/ac (chelate forms) may correct deficiency.

Starter fertilizer research with soybean generally indicates little or no advantage to banded fertilizer treatments relative to broadcast. Seed-placed (pop-up) fertilizer is not advised due to the potential for seedling damage (salt-sensitivity).