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.