Slow release nitrogen fertilizers

MSU field trials indicate that ESN is just as effective and has many benefits compared to anhydrous ammonia, urea and UAN.

Efficient nitrogen (N) fertilizer use is increasingly important with rising costs and potential environmental concerns. Important N management decisions are choosing the right rate, source, timing and placement. Common N fertilizers such as anhydrous ammonia (82% N), urea (46% N) and urea ammonium nitrate (UAN) (28% N) are susceptible to losses from leaching, denitrification, and volatilization, especially if all N is applied early in the season. In corn, peak N uptake occurs when plants are 12-15 inches tall (about six weeks after planting). In humid climates, spring rainfall and temperature conditions are unpredictable and predispose N loss to the environment.

Michigan State University currently recommends about 20 to 40 lbs. N/A as a starter with the balance of crop N needs side-dressed in June, based on yield goal and pre-sidedress soil nitrate test (PSNT). This is a rational approach, but some corn producers have reservations because of the narrow application window, unpredictable rain, added fuel costs and time demands on soil sampling and side-dressing. Low-cost anhydrous ammonia is losing favor because of liability, theft and freight issues and increasing application costs. New controlled-release fertilizer technology gives farmers the convenience of applying N ahead of planting while potentially achieving high N efficiencies and minimizing environmental risks.

Environmentally Smart Nitrogen (ESN®) is urea coated with a semi-permeable polymer, resulting in a temperature-controlled N release in synchronization with corn growth and N uptake.

Michigan State University Extension field trials in 2006 and 2007 demonstrated that ESN, particularly the pre-plant incorporated treatments, were as effective as anhydrous ammonia, urea and UAN in terms of corn yield and quality. Other ESN benefits include reduced N leaching potential, flexibility in application timing and lower application costs. Moreover, social, economic, and sustainability issues have generated a compelling need to find alternatives to anhydrous ammonia.

Environmentally Smart Nitrogen has potential to be used on other Michigan crops. On wheat, Michigan studies have shown that ESN top-dressed prior to green up was as effective as urea or UAN. Blending ESN with urea is another option to provide immediate and long term N availability to wheat.

The high commodity prices have provided farmers incentives to opt for more convenient and environmentally friendly N sources such as ESN. Higher efficiencies and ease of use with potential to eliminate multiple field passes may offset higher cost of ESN (about $0.10/lb. N higher than urea). The local ESN distributor estimates that ESN will be used on over 25,000 acres of corn and wheat in Eaton County this year.

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