Broadcast and Deep-Band Phosphorus and Potassium Placement In Strip-till and No-till for Corn and Soybean.

Fertilizer placement can be a useful management tool to improve nutrient availability in conservation tillage systems. Certain placement methods, however, can result in non-uniform distribution of nutrients in the soil making it difficult to determine whole-field fertility by traditional sampling strategies. The objectives of this project were to determine the impact of phosphorus (P) and potassium (K) placement on rainfed corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield and to quantify changes in the distribution of P and K levels in the field. The study was conducted on a corn-soybean rotation with crops planted at 76 cm row-spacing in highly productive soils at three locations near Tolono, Illinois. In fall 2007 and 2009, before the corn crop, applications of 0, 52, 77, 103, 129, 155, and 180 kg P₂O₅ and K₂O ha^-1 were broadcast-applied in no-till (NTBC) and strip-till (STBC) and deep banded, 15 cm below the surface, at the crop-row position in strip-till (STDB) using real time kinematic (RTK) satellite navigation. Every fall grain yield was measured and soil samples for P and K measurement were collected and kept separate from the 0-10, 10-20 and 20-30 cm depth increment at 0, 19, 38, and 57 cm from the crop-row position. There was no response in corn or soybean yield to fertilizer rate or placement. Strip-till corn yielded 11.9 Mg ha^-1, a 0.5 Mg ha^-1 increase relative to no-till.  Across rates, subsurface banding resulted in a decrease in P and K levels in the surface and a substantial increase at the point of application while broadcast applications increased surface levels. However, whole-field fertility was similar for all systems. Subsurface banding may be useful to reduce P levels, without a negative impact on crop production, in areas where runoff from high-P surface levels possess an environmental risk.