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Corn+Soybean Digest

Panelists Discuss Fertilizer Strategies

Growers can save fertilizer and improve crop yield by using the four Rs of nitrogen (N) management: right source, right rate, right time and right place. That’s according to Cliff Snyder, N program director with the International Plant Nutrition Institute. Snyder was one of three experts speaking at the 2009 Commodity Classic in Grapevine, TX. His remarks were part of a Learning Center panel titled “Nitrogen Strategies for a New Millennium” sponsored by Honeywell.

“At best, it’s estimated that the corn crop takes up 60-70% of N applied in the growing season, but more commonly the number is probably under 50%,” says Snyder. “Moving forward, it’s essential that we raise that bar, both in order to reach the full yield potential of new corn genetics and to alleviate environmental concerns that could lead to N regulation.”

Snyder pointed to substantial N loss from denitrification in water-logged corn fields last spring. In addition to reducing yield potential, denitrification releases nitrous oxide, a greenhouse gas that is about 300 times more potent than carbon dioxide and roughly 10 times more potent than methane. Nitrogen loss also occurs through volatilization of surface-applied urea-containing sources and leaching of N in the nitrate form.

“Denitrification and other processes that contribute to N loss and reduced yield potential result in ‘leakage’ of N into the environment,” says Snyder. “These losses can be mitigated through proper management of N source, rate, timing and placement.”

John Sawyer, professor and extension specialist with Iowa State University, addressed a growing need for sulfur fertilization and presented new data from northeast Iowa demonstrating yield increases when alfalfa and corn were fertilized with sulfur- containing fertilizers.

Sawyer reports that alfalfa production on sulfur-deficient soils was doubled with sulfur application. There was no response when soils supplied adequate plant-available sulfur and plant tissue sulfur concentrations were above critical values.

On corn, response to sulfur application occurred in 28 of 45 Iowa sites in 2007 and 2008. Averaged over all sites, sulfur increased corn yield by 13 bu./acre. On responsive sites, the average yield increase was 28 bu./acre on coarse-textured soils and 15 bu. on fine-textured soils.

Sawyer attributes the sulfur responses to several factors, including soil properties such as coarse texture, low organic matter, eroded and side-slope landscape positions, no manure application and a reduction in atmospheric sulfur deposition from industrial emissions over the past 30 years.

Fred Below, plant physiologist with the University of Illinois, concluded the session with a discussion of N uptake in modern corn hybrids, including triple-stacks that combine resistance to glyphosate, corn borers and corn rootworms.

“A comparison of corn hybrids over the last 25 years demonstrates that modern genetics are better able to capture N from the soil,” says Below. “As a result, today’s hybrids only require 0.9 lb. of N/bu. compared to 1.2 lbs. needed by their older counterparts.”

Below also discussed ways in which future biotech N traits can be expected to improve fertilizer N use and yield, and he presented field data suggesting that the rootworm trait may have already altered N use.

“We have seen large improvements in grain yield and N use in hybrids containing the rootworm trait that we cannot completely attribute to rootworm control,” Below says. “Most of the improvement in N use is in the uptake of N, with N recovery efficiencies increasing from around 50% to nearly 75% in the rootworm hybrids. These results suggest that there are changes in rooting and nutrient capture in rootworm-resistant corn hybrids that are delivering more N and probably other mineral nutrients to the growing plant.” Studies will continue in 2009.

The panel was moderated by Dean Collamer, agronomist with Honeywell. Click here for more information.
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