Getting the most from nitrogen

by Deborah Jeanne Sergeant

To decrease waste on the farm, it is vital for producers to ensure they get the most value out of their inputs. Dr. Quirine Ketterings, nutrient management specialist with Cornell University, presented “Getting the Best Bang for Your Nitrogen Buck” at the recent 2022 virtual Corn Congress.

Because nitrogen planning and management challenge producers, they need to better understand its use. “Soil organic matter contains nitrogen, but it will need to be mineralized during the growing season,” Ketterings said.

Cover crops can supply nitrogen for the next growing season. Alfalfa/grass, hay and soybeans can all supply nitrogen, as can manure. “Fertilizer definitely has a role,” she added. “We don’t want to shorten our crops.”

Measuring yield is one way farmers can better manage their nitrogen. “Each farm has fields that yield below the farm average,” Ketterings said. “Some fields are stable yielding over time; others are incredibly variable. When you measure yield, you get a better sense of crop needs and growth limitation.”

Ketterings outlined a few management strategies to help farmers. The first is to rank field yield from low to high to develop effective strategies to address nitrogen shortages in particular areas.

“Some fields are simply lower yielding than others and there’s little you can do about it,” she said. “If you have yield monitor data, evaluate your maps.”

Some farmers “retire” an area such as a low-yield headland from crops and use it for perennial hay or conservation purposes. They could also choose to repair the headland with improved management to increase the soil’s productivity. However, if a parcel can’t be “fixed,” reduce inputs to reflect that lower yield potential.

Another management strategy is to rotate crops. The first year after alfalfa/hay is the cheapest one in which to grow corn, as it requires only starter nitrogen. Corn following soybeans or overwintering cereal cover crops can do this with lowering the amount of nitrogen by about 30 pounds/acre.

“Credits can be much higher with earlier seeded cover crops – about 70 to 80 pounds of nitrogen per acre,” Ketterings said. “Take rotation credits when determining how much nitrogen to apply for the next corn crop.” She added that when winter cereals like cereal rye, triticale or wheat are harvested for forage, some fields show a yield response to nitrogen at green-up while others do not.

Contributors to low yield can include drainage issues, no autumn manure application and planting after Oct. 1. Farms with good soil drainage typically do not need application. Those with poor drainage but “manure history” and planting before Oct. 1 also don’t need an application. But those without manure history or planted after Oct. 1 typically require application. The rate suggested was 60 to 90 pounds of nitrogen/acre.

Ketterings underlined the importance of manure, which possesses all 17 essential nutrients, including organic and mineral nitrogen. Its nitrogen can release for three years. For the largest impact from manure, direct incorporate/inject it at planting or apply it during the growing season. She noted this can increase efficiency by up to 50%. Deep tillage is not necessary to increase the effectiveness of manure providing nitrogen benefits.

If it’s determined farmers still need nitrogen fertilizer, though, a timely split application can save money. “Split apply at V4 through V6,” Ketterings said. “If you’re delayed, adjust rates, as yield is already compromised.”

Ketterings said operators should consider enhanced efficiency nitrogen sources only when nitrogen is needed and nitrogen losses are likely (such as through surface-only application). To optimize fertilizer management, “in-season adjustments are something to look at,” she said.

Looking at yield data can help. “All adjustment tools ask what your target yields are,” Ketterings said. It’s important to monitor fields with check spots or test strips. “And remember, you cannot fertilize yourself out of a drought,” she said. Conversely, fertilizer cannot compensate for oxygen deficiencies in saturated soil.

She encouraged farmers to make use of available tools to see where cuts in applications can possibly be made. “Strive for improvement, not perfection,” she said. “This is the year to learn how to manage nitrogen. Consider end-of-season evaluations. This is what we call adaptive management.”

A cornstalk nitrate test can provide information on how much nitrogen was available to plants and help producers know where they can make changes in the future to apply the proper amounts.

“This is the year for single strips, to test if you can be comfortable in making adjustments,” Ketterings said. She said a strip at least two harvester widths wide and the field length through zones of interest can provide helpful data. “You should have at least three years of yield data for the field; the more, the better,” Ketterings said.

Ketterings invited any farmer interested in setting up a joint on-farm research partnership to contact her at qmk2@cornell.edu.

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