Strip-till for corn and soybean production is an alternative to no-till on many poorly drained northern Corn Belt soils because it provides a warmer, tilled seedbed while maintaining substantial amounts of erosion-minimizing plant residue between the tilled strips.
Traditionally, fertilizer phosphorus is banded 6 to 7 inches deep in the strips when strip-tilling. Banding 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 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 — popup, in the seed furrow as well as banded 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, fertilizer phosphorus was placed as single popup, deep-banded or broadcast and as a dual application (deep-banded and popup) on both low and very high phosphorus-testing soils for 3 years of corn and soybeans.
On low-to-very-low phosphorus-testing soils, popup placement of phosphorus produced greater corn yields than deep banding or broadcasting in some years. But in other years, the differences among the phosphorus placements were not seen.
Early growth and phosphorus uptake on these soils were consistently greatest for popup placement and sometimes lowest for deep-band placement. On the high and very high phosphorus-testing soils, yields weren’t 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. Apparently, the small corn roots grow out to the side and then down, missing the banded phosphorus, resulting in early plant growth not being different than the zero-phosphorus control.
Adding phosphorus as an in-furrow, seed-placed popup to the deep-banded phosphorus produced an ideal solution. Sometimes it gave the greatest yield of any of the treatments. The phosphorus placement was not an issue for strip-tilled 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 popup fertilizer should produce highest yields and greatest phosphorus efficiency.