By Fabian Fernandez and Jeff Vetsch
With high fertilizer prices, farmers are looking for alternatives to make every pound of nitrogen (N) fertilizer count. Is now the time to try controlled-release polymer-coated urea?
Urea vs polymer-coated urea, 24 hours after application. The polymer-coated urea is still on the surface whereas the urea has started to hydrolyze and some was probably lost by volatilization as NH3. Please note that applying polymer-coated urea on the soil surface (as pictured) is not suggested, as heavy rainfall can lead to runoff of the granules that float with water.
To be as efficient as possible with nitrogen, the most important thing you can do is to follow our soil fertility best management practices (BMPs), which have been established through years of unbiased research. While nitrogen management discussions are often centered around nitrogen rate, it is important to recognize that the right rate is just one of the 4Rs of nutrient management. Applying the right rate of nitrogen fertilizer but not using the right nitrogen source, placement or timing can lower your nitrogen use efficiency, and therefore your profitability, especially when fertilizer prices are high.
What is polymer-coated urea?
Polymer-coated urea is urea coated with a water-permeable polymer coating to protect the urea granules from early season N loss. The nitrogen in urea can be lost via leaching and denitrification if there is excessive rainfall soon after application. Polymer-coated urea helps protect against this risk. As the soil warms over time, the polymer coating is broken down by soil moisture, releasing nitrogen to the soil. The most common polymer-coated urea product on the market is ESN® (Environmentally Smart Nitrogen). Polymer-coated urea costs more than urea and other nitrogen fertilizer products, usually around $0.16 to $0.20 more per pound. As with urea, it is important to broadcast and immediately incorporate polymer-coated urea into the soil with tillage.
What does research in Minnesota say?
Our research comparing urea and polymer-coated urea in Minnesota has shown mixed results, based primarily on the weather conditions in the year and location of each study. During wet years, polymer-coated urea usually outperforms urea, while during dry years they perform similarly. This means that during wet years, polymer-coated urea is often worth the added cost, while in dry years it is not. Unfortunately, we can’t predict the future, but recent history and climate models suggest that Minnesota is getting wetter.
Soil type also plays an important factor. For example, on a sandy loam soil near Becker in 2014 and 2015, polymer-coated urea had a 39 bushel per acre yield advantage versus urea. However, at research sites on fine-textured soils in southern Minnesota in those same years, the treatments showed no yield difference between polymer-coated urea and urea.
As with most agronomic decisions, you’re not going to be right every year. In a large study of 35 locations around Minnesota from 2014 to 2018, we found that polymer-coated urea had a yield advantage over urea 26% of the time for corn-following-corn and 28% of the time for corn-following-soybean. Most of the sites were on fields with high N loss potential due to weather or soil conditions yet polymer-coated urea never reduced yields relative to urea.
What ratio of urea to polymer-coated urea should I use?
Because polymer-coated urea 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. Blending urea and polymer-coated urea is another good way to get some of the benefits of polymer-coated urea while minimizing costs. Wet, poorly-drained fine-textured soil conditions, which are common in south-central Minnesota, are a good example of a situation where a 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, polymer-coated urea increased revenue $49.50 per acre compared to urea, but a blend of two parts polymer-coated urea to one part urea (2:1 blend) increased revenue $85.50 per acre and a 1:2 polymer-coated urea to urea blend increased revenue $72.50 per acre. So it seems to make sense to incorporate some urea into your blend. However, we used suboptimal N rates in the study so it was easier to identify treatment differences. Revenue differences would be less striking for N rates closer to the maximum return to N rate.
Should currently high nitrogen fertilizer prices impact my purchasing decisions?
As nitrogen fertilizer prices have risen, so have prices for polymer-coated urea. Historically, polymer-coated urea costs around $0.20 per pound more than urea. We called a southern Minnesota ag retailer to check on the price difference and polymer-coated urea currently costs $0.22 more per pound of N than urea. (Polymer-coated urea is 44% N by weight and costs $1,040 per ton while urea is 46% N by weight and costs $885/ton.) Because this is so close to the historical data, our above recommendations are unchanged.
What current research on polymer-coated urea is going on in Minnesota?
In 2021, we began a new study to investigate the potential benefits of using polymer-coated urea as a nitrogen source. While the earlier research was highly useful and relevant, those studies were conducted with single nitrogen rate comparisons that do not allow us to fully calculate the potential economic benefits of such treatments. One potential drawback of polymer-coated urea, as previously mentioned, is that it costs more than urea. So, it is important to weigh the benefits against the added cost when deciding whether to purchase polymer-coated urea instead of urea.
The current study is designed to evaluate polymer-coated, urea, and various polymer-coated urea and urea blends with different application timings in several locations around Minnesota. We’ll evaluate the grain yield response of corn to nitrogen rates to determine the most profitable nitrogen rate with these treatments.
Unfortunately, the first year of the study showed little or no difference between treatments. This is because the potential for nitrogen loss was very low due to the 2021 drought. Water limitations negatively affect yields to a much larger extent than differences in nitrogen management.
We will be conducting the study again this year, so stay tuned for more information from this project.
Thanks to the Agricultural Fertilizer Research and Education Council (AFREC) and the Minnesota Corn Research and Promotion Council (MCRPC) for funding these studies.
Source : umn.edu