Despite the trend toward higher soil fertility levels, starter fertilizers remain a good investment for many Wisconsin corn growers. The potassium in starter fertilizers can be especially helpful in reduced-tillage systems, says a University of Wisconsin-Madison researcher.

Some reduced tillage systems may have higher than expected needs for potassium, according to Larry Bundy, a soil scientist at the UW-Madison”s College of Agricultural and Life Sciences. Starter fertilizers in reduced tillage systems may help overcome the effects of soil compaction, low soil temperatures, high soil moisture, and other factors that can reduce early season corn growth, he says.

Minnesota researchers found potassium deficiencies in ridge-till corn even at high soil test levels, and showed that banded potassium additions minimized the deficiencies. Studies in Iowa showed that no-till corn responded to deep-banded potassium at sites with high soil potassium levels.

In Wisconsin trials, Bundy found that starter fertilizer applied at later no-till planting dates stimulated early season plant growth compared with corn that received no starter. This early growth spurt allowed the plants to attain more of their yield potential before the end of the growing season. In on-farm studies, corn responses on high-testing soils were more likely at later planting dates or with longer season hybrids, he reports.

On a variety of tillage systems in Wisconsin, Bundy found that corn response to starter fertilizers on high-testing soils was more likely at soil potassium levels below 140 parts per million. CALS soil scientist Dick Wolkowski showed that in conventional tillage, banded potassium additions partially offset corn yield reductions in compacted soils, even at relatively high soil potassium levels.

On high testing soils, response to starter fertilizer is most likely with late planting dates and with long-season relative maturity hybrids. Bundy thinks that responses at high soil fertility levels are probably due to placement effects that enhance early season growth or help overcome nutrient-uptake limitations imposed by the management system.

“In general, use of starter fertilizers for corn may be more important in no-till or reduced tillage systems than in conventional tillage,” Bundy says. “Potassium in starter appears to be particularly important in reduced tillage, since responses to applied potassium can occur even at high soil test levels.”