Assessment of Soil Phosphorus and Potassium following Real Time Kinematic-Guided Broadcast and Deep-Band Placement in Strip-Till and No-Till

Fertilizer placement may cause non-uniform nutrient distribution in the soil, making it difficult to determine whole-field fertility by traditional sampling strategies. Our objectives were to determine P and K distribution after repeated applications in no-till and strip-till soils and to develop improved sampling procedures to estimate soil P and K levels on a corn (Zea mays L) and soybean [Glycine max (L.) Merr.] rotation with crops planted at 76-cm row spacing. Three trials near Pesotum, IL, received blends of 0-0, 22-42, 33-62, 44-83, 55-104, 66-125, and 77-145 kg P-K ha(-1) in fall 2007 and 2009 before corn planting. Applications were broadcast-applied in no-till (NTBC) and strip-till (STBC) and deep-banded in strip-till (STDB) 15 cm below the surface in the crop row OR) using real-time kinematic (RTK) satellite navigation. Every year soil P and K was measured at 10-cm increments to a 30-cm depth at 0, 19, 38, and 57 cm from the IR. Subsurface banding reduced P and K levels in the surface and increased them at the point of application, or deeper with the highest rate, while broadcast applications increased surface levels. Soil-surface K levels were greater at IR likely because of K leaching from senescing standing crops. Soil-test results indicated no need to adjust fertilizer rate based on tillage or fertilizer placement. A sampling ratio of 1:3 IR to between the crop rows (BR) seemed adequate to estimate soil fertility across a wide range of P- and K-fertilizer rates and soil test levels where the location of the fertilizer band or planting row is maintained constant.