Phosphorus 4R Management and Economics in Strip-Tillage Systems.

In the US Midwest, it is customary for producers to apply two-year recommended phosphorus (P) rates as one application, especially in corn (Zea mays L.)-soybean (Glycine Max L. merr) rotations. This management practice might prove economical due to lower application costs. However, soybean yields may be limited due to inadequate P levels, especially if corn yields and P removal rates are high. A long-term study evaluating the residual P and fertilizer effects on soybean yield was established in 2006 at two locations in Kansas. Residual P fertilizer treatments for soybean were made prior to planting corn at a total rate of 20 and 40 kg P ha^-1 as broadcast (BC) and combination broadcast with starter (BC+ST) applications. Direct fertilizer treatments to soybean consisted of 20 and 40 kg P ha^-1 combination broadcast with starter (BC+ST) applied to corn with an additional 20 kg P ha^-1 applied as broadcast to soybean at planting. Treatments containing starter (5cm to the side and 5cm below seed) consisted of 10 kg P ha^-1 application rate at planting with the remaining P applied as broadcast. Results show increased soybean yield with the additional P fertilizer application suggesting that P application rates were inadequate for the two-year rotation. A partial economic analysis of the management systems show an economic benefit on soybean production with applications of starter before corn. Based on this study, producers should consider P removal rate of all crops in their rotations if one time applications are made. Additional P may be needed to maximize soybean production.