Deep Banding Phosphorus and Potassium Fertilizers for Corn Managed with Ridge Tillage

Broadcast fertilization leads to stratification of soil P and K in the ridge‐till system, which may reduce fertilizer use efficiency. This study evaluated the response of corn ( Zea mays L.) to broadcast or deep‐band (15‐ to 20‐cm depth) placements in 15 site–years. Fertilization rates were 0 to 56 kg P ha −1 and 0 to 132 kg K ha −1 Soil‐test P (STP) and K (STK) were higher in the top 15‐cm layer of the ridges. Phosphorus increased early plant growth (V5 stage) in five sites, early P uptake in nine sites, and grain yield in seven sites. Yield was increased by P when STP was <22 mg P kg −1 (Bray‐1) in the top 15‐cm layer of ridges or <18 mg P kg −1 in the top 15 cm of ridges and valleys. The P placements seldom differed (the deep‐band P was better in one site). Potassium increased growth in 6 sites, K uptake in 14 sites, and grain yield in nine sites. The deep‐band K increased yield over the broadcast K in four sites. The yield response to broadcast K across sites was not correlated with STK, but the response to deep‐band K was negatively and linearly correlated with STK from various sampling positions. Corn responded to deep‐band K in soils with above‐optimum STK according to current soil‐test interpretations. The results showed that both placements usually were similarly effective for P, and that deep banding often was superior for K.