Are controlled-release nitrogen fertilizer products worth the cost?

By: Jared Spackman, graduate research assistant, and Fabian Fernandez, Extension nutrient management specialist

Recent wet years in Minnesota are causing nitrogen management issues for corn farmers. Wet falls can delay harvest and push fieldwork to the spring, wet springs can limit field access and delay fertilizer applications and planting, and variable in-season growing conditions can hurt yields. Can controlled-release nitrogen fertilizer sources help?

Environmentally Smart Nitrogen (ESN)

Each urea granule of ESN is coated with a water-permeable polymer coating. After field application, soil moisture diffuses into the granule, creating a fertilizer solution that then diffuses back into the soil.

As the soil gets warmer, more of the nitrogen (N) in ESN is released to the soil. Experimental research has shown that ESN applied to soil held at a constant temperature of 59℉ for 40 days released only 29% of the fertilizer N while at 66℉, 87% was released.

While this helps limit nitrogen loss, it can also mean that not enough N is released early in the growing season if it’s not warm enough. This means that applying soon before planting can be risky, depending on how warm the soil is. The key challenge is to match up ESN’s N release with crop timing needs.

ESN is also more expensive than urea, $0.16 to $0.20 more per pound. It is most valuable when the potential for N loss is high. ESN can limit N loss from leaching and denitrification, compared to urea, if there is excess rainfall soon after application.

Research in Minnesota

ESN has shown to have a strong effect on coarse-textured soils. Our research on sandy loam soil near Becker, Minnesota in 2014 and 2015 showed a 39 bushel per acre (bu/ac) yield advantage with ESN vs urea. Both were applied in the spring at a rate of 120 pounds per acre (lbs. N/ac). The yield improvement was equivalent to applying 200 lbs. N/ac pre-plant urea.

However, at research sites on fine-textured soils in southern Minnesota in 2014 and 2015, the same treatments showed no yield difference between ESN and urea. Fine-textured soils are less prone to N leaching losses.

In a larger study of 35 locations around Minnesota from 2014 to 2018, we found that ESN had a yield advantage over urea 26% of the time for corn-following-corn and 28% of the time for corn-following-soybean. In addition, most of the sites were on fields with high N loss potential due to weather or soil conditions. However, ESN never reduced yields relative to urea. Both ESN and urea were broadcast and immediately incorporated with tillage. This is important to minimize N loss from volatilization and reduce the loss potential from runoff if excessive precipitation occurs soon after application. 

ESN-urea blends

Because ESN is more expensive than urea, it is a good idea to target fields or areas of fields with high potential for early-season N loss. ESN-urea blends are also a good way to get some of the benefits of ESN while minimizing costs. Wet, poorly-drained fine-textured soil conditions that often occur in south-central Minnesota are a good example of a situation where an ESN-urea blend could reduce the risk for N loss early in the season and provide readily-available N to support early crop growth.

According to our studies, ESN increased revenue $49.50 per acre compared to urea, but a blend of two parts ESN to one part urea (2:1 ESN-urea blend) increased revenue $85.50 per acre and a 1:2 ESN-urea blend increased revenue $72.50 per acre.

These values were calculated assuming a $0.20 premium for ESN versus urea but the same application cost ($0.50 per pound) and a $3.50/bushel corn grain price. While revenue differences would be less striking for N rates closer to the maximum return to N rate, we used suboptimal rates in the study so that it was easier to identify treatment differences.

ESN is just one management practice that can help protect your nitrogen fertilizer investment. Other fertilizer sources or management practices, including split applications (a must on sandy soils) may provide the same or greater benefit for crop production. Additionally, weather conditions may not justify the additional cost of a premium product in all years. However, due to the unpredictable nature of weather patterns, incorporating ESN into your nitrogen fertilizer plan may be a good form of insurance.

These projects were funded by the Agricultural Fertilizer Research and Education Council (AFREC) and the Minnesota Corn Research and Promotion Council (MCRPC).

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