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.
Gyles Randall, University of Minnesota soils scientist, says phosphorus is typically 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," Randall says. "However, little research has been conducted to determine the optimum placement of phosphorus in strip-till systems."
Two studies were conducted between 1997 and 2007 to determine the effects of phosphorus placement on corn and soybean production on low and high phosphorus-testing soils at Waseca, Minn.
One study compared two fertilizer phosphorus placement positions in the seed furrow with pop-up and 6 to 7 inches deep in the strip; and a zero-phosphorus control for 6 years of corn and 6 years of soybeans.
In the other study, phosphorus was placed as single pop-up, deep-band or broadcast applications and as a dual application (deep-band plus pop-up) on low and very high phosphorus-testing soils for 3 years of corn and soybeans.
"On low to very-low phosphorus-testing soils, pop-up placement of phosphorus produced greater corn yields than deep-band or broadcast application in some years," Randall says, "but in other years differences among the phosphorus placements were not seen.
"Early growth and phosphorus uptake on these soils were consistently greatest for pop-up placement and sometimes lowest for deep-band placement. On the high and very-high phosphorus-testing soils, yields were not affected by any of the phosphorus placement positions."
The inconsistent and sometimes less-than-optimum performance of deep-band placement on lower-testing soils was not expected, Randall says. Apparently, Randall believes the small-corn roots grow out to the side and then down, missing the band-placed phosphorus, resulting in early plant growth not being different than the zero-phosphorus control.
"Adding phosphorus 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," he says. "The phosphorus placement was not an issue for strip-till corn production on neutral to acidic, high and very-high phosphorus-testing soils.
"However, if soil test phosphorus is less than high, a combination of deep-band and seed-placed pop-up fertilizer should produce highest yields and greatest phosphorus efficiency."