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With transgenic corn rootworm hybrids’ widespread adoption, it may be time to rethink high-yield corn fertility, says Fred Below, University of Illinois plant physiologist.
Research conducted by Below and grad student Ross Bender shows that rootworm hybrids’ roots are active longer after flowering than conventional corn’s roots. This increases nutrient uptake, especially of nitrogen, phosphorus, potassium and zinc.
“We would argue that soil-fertility recommendations might be out of date for the yield goals that are achievable with today’s hybrids,” Bender says.
With the increased uptake, phosphorus is of special concern, given current fertility practices, says Below. Surveys show that on average, Illinois farmers apply just over 90 pounds per acre phosphorus in a corn and soybean rotation. Since corn and soybean harvest removes about 80% of phosphorus, Illinois soils are being depleted of phosphorus at the rate of 30 pounds of P2O5 per acre every two years, he estimates.
“This suggests a looming phosphorus-soil fertility crisis if adequate phosphorus-application-rate adjustments aren’t made as productivity increases,” Below says.
Fully filled corn ears indicate that the supply of soil nutrients — including P, S and Zn — was adequate to meet crop demand.
When it comes to high-yield corn environments, nitrogen gets well earned respect as the most critical element in a fertility program. But three key nutrients’ under-recognized importance – sulfur, zinc and the long-recognized standby, phosphorus – could limit yields from an otherwise well-fertilized crop, says University of Illinois Plant Physiologist Fred Below.
“These are the missing links for high-yield corn,” says Below. “Many farmers don’t fertilize for sulfur and zinc. And many people don’t realize the season-long importance of phosphorus.”
In research conducted by Below and graduate student Ross Bender, extra phosphorus, sulfur and zinc increased corn yields 8-10 bushels per acre in fields already supplied with a balanced high-yield fertility program. “We have seen yield increases greater than would be expected based on the phosphorus soil test,” says Below. “Phosphorus’ uptake rate is greater than what many soils can supply based on the soil test.
“I’m also convinced that at yields above 200 bushels per acre, there are many cases where yields are being limited by sulfur and zinc,” adds Below. “I don’t think that soil fertility has kept up with today’s hybrids’ yield potential.”
His research tracked six hybrids for site-years at Urbana, Ill. (2010) and DeKalb, ll. (2010). The recommendations for phosphorus, sulfur, and zinc apply to both transgenic insect protected corn rootworm hybrids and non-protected hybrids. Research also suggests that the insect-protected hybrids may have additional nutrient accumulation later in the season (because of healthier, more active roots), especially when there is a yield increase as a result of the insect protection. “With the quantity of hybrids and locations tested, we’d feel this is generally representative of most modern corn hybrids currently used,” University of Illinois Crop Physiology Graduate Student Ross Bender says. “We evaluated five hybrids at DeKalb and six hybrids at Champaign during 2010 (one trial at each location). The five hybrids grown in DeKalb were also grown in Champaign plus one additional hybrid.”