Optimum placement of phosphorus for corn/soybean rotations in a strip-tillage system

Strip tillage, a conservation tillage system using very reduced tillage, is attracting much attention throughout the corn-growing regions of the United States. In the northern parts of the Corn Belt, strip tillage often replaces no-till systems on the more poorly drained soils because it provides a warmer tilled seedbed for early planting and faster early growth while maintaining substantial amounts of erosion-minimizing plant residue between the tilled strips. Another benefit of strip tillage is the need for only one field operation between soybean harvest and spring planting—that is, fall strip tillage accompanied by deep-placement of fertilizer phosphorus (P) and potassium (K) in a band 15 to 18 cm (6 to 7 in) deep in the strip. No preplant tillage is needed. From an environmental perspective, deep-band placement is considered to be ideal in terms of eliminating nutrient stratification and reducing the potential for surface runoff of fertilizer P, which can easily occur when fertilizers are broadcasted on the soil surface of no-till systems. From an agronomic perspective, fertilizer placement 10 to 13 cm (4 to 5 in) directly below where the seed will be planted is thought to be ideal in terms of fertilizer P and K use efficiency, early …