Best phosphorus placement with strip tillage depends on soil test

By Gyles Randall, University of Minnesota Extension

ST. PAUL, Minn. (10/27/2008)—Strip tillage for corn and soybean production is an alternative to no tillage on many poorly drained northern Corn Belt soils. It provides a warmer tilled seedbed while maintaining substantial amounts of erosion-minimizing plant residue between the tilled strips.

Traditionally, fertilizer phosphorus (P) is band-applied 6 to 7 inches deep in the strips at the time of strip tillage. This placement is thought to be ideal in terms of fertilizer use efficiency, early plant growth, and high yields. However, little research has been conducted to determine the optimum placement of P in strip-till systems.

Two studies were conducted between 1997 and 2007 to determine the effects of P placement on corn and soybean production on low and high P-testing soils at Waseca. One study compared two fertilizer P placement positions [in the seed furrow (pop-up) and 6 to 7 inches deep in the strip (deep-band)] and a zero-P control for six years of corn and six years of soybeans. In the other study, fertilizer P was placed as single pop-up, deep-band or broadcast applications and as a dual application (deep-band + pop-up) on low and very high P testing soils for three years of corn and soybeans.

The bottom line: On low to very low P-testing soils, pop-up placement of P produced greater corn yields than deep-band or broadcast application in some years, but in other years differences among the P placements were not seen. Early growth and P uptake on these soils were consistently greatest for pop-up placement and sometimes lowest for deep-band placement. On the high and very high P-testing soils, yields were not affected by any of the P placement positions.

The inconsistent and sometimes less-than-optimum performance of deep-band placement on lower testing soils was not expected. Apparently, the small-corn roots grow out to the side and then down, missing the band-placed P, resulting in early plant growth not being different than the zero-P control.

Adding P as an in-furrow, seed-placed pop-up to the deep-band treatment produced an ideal solution, sometimes giving the greatest yield of any of the treatments. The P placement was not an issue for strip-till corn production on neutral to acidic, high and very high P-testing soils. However, if soil test P is less than high, a combination of deep-band and seed-placed pop-up fertilizer should produce highest yields and greatest P efficiency.

Any use of this article must include the byline or following credit line:
Gyles Randall is a soil scientist with the University of Minnesota.

Media Contact: Catherine Dehdashti, U of M Extension (612) 625-0237, ced@umn.edu

URL: http:// www.extension.umn.edu/extensionnews/2008/phosphorus-placement.html  This page was updated Oct. 24, 2008 .
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