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 diffi cult 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 (IR) 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.