Grain Yield, Early Growth, and Nutrient Uptake of No‐Till Soybean as Affected by Phosphorus and Potassium Placement

More information is needed about P and K placement for no‐till soybean [ Glycine max (L.) Merr.]. This study evaluated plant responses to P and K fertilization and placement in 10 long‐term trials and 11 short‐term trials in Iowa from 1994 to 1997. Treatments were various P and K rates broadcast, banded with the planter, and deep banded (at a 15‐ to 20‐cm depth). Measurements were plant weight, P uptake, and K uptake at the V5 stage and grain yield. Phosphorus fertilization increased yield when soil‐test P (STP) was less than 9 mg P kg −1 (Bray‐P 1 ) at a 0‐ to 15‐cm depth or 12 mg P kg −1 at a 0‐ to 7.5‐cm depth. The P placement did not influence yield. The band K placements produced slightly higher yield than the broadcast placement. Responses to K were not related to soil‐test K (STK) levels, which varied from 90 to 262 mg K kg −1 (ammonium acetate), or stratification. The P or K placement had little influence on early growth but influenced early P and K uptake. Banding with the planter was more effective than broadcasting for P uptake, and the two band placements were more effective for K uptake. Only the responses of K uptake and grain yield to banded K were correlated across sites. A shallow sampling depth will improve only slightly the prediction of response to P. The observed small no‐till soybean yield response to banded K would seldom offset increased application costs in similar soils.