ESN® (Environmentally Smart Nitrogen)
The geographic framework shown here delineates spatial units with shared soil and climatic properties, where one might expect agronomic tools and/or products to perform similarly, if all other farm management variables are constant. ESN® trials conducted using urea, UAN or both are super-imposed on the framework, which we refer to as Technology Extrapolation Domains or TEDs. Please see the text below for more explanation of how this framework is being used to show trial results.
Field trials play an important role in the testing and implementation of new agricultural products and management practices. Properly conducted trials give a good indication of a products’ performance in the soil and climatic conditions present at the trial site. However, extrapolating results from field experiments conducted at one or more locations to a larger, spatially explicit domain has been a major challenge confronting agronomic science due to the large variation in soil properties and climate governing crop response to management.
The heart of the challenge is to achieve a balance between having a spatial scheme that is so coarse that environmental variation within a technology extrapolation domain (TED) is large—leading to substantial variation in performance of a given technology, or so fine that the number of field study locations and data requirements are overwhelming. Recent advances in geographic information technologies and publicly accessible databases on soils and climate now make it possible to establish such a framework.
The framework NutrientStar uses draws heavily on the spatial scaling protocols developed to support the Global Yield Gap Atlas developed by Drs. Ken Cassman, Patricio Grassini, Justin Van Wart and the University of Nebraska.
The TED framework delineates spatial units with shared soil and climatic properties, where one might expect agronomic technologies to perform similarly, all other variables being constant. On the map above, TEDs are depicted as colored regions with trial locations indicated by icons, which are colored according to fertilizer form. These TEDs correspond to the areas of greatest rain-fed corn production in the US.
The tables below provide information about yield impacts of ESN® in plot studies grouped according to the TED where the study was conducted. The NutrientStar team had to estimate which TED a study was located within, because precise GPS coordinates were not provided for most plot studies. To make this estimate, a buffer of 5 km was drawn around each study location, and the TED represented by the largest number of pixels within the buffer was chosen as the TED for that study, after eliminating all pixels without corn/soybean production. The column in the table showing the estimated TED for each study is entitled “Plurality TED”.
The confidence level for each grouping of studies is the percentage of pixels within the 5 km buffer representing the plurality TED – again, after eliminating all pixels without corn/soybean production. Confidence levels are categorized and color-coded as: high confidence (greater than 75% of pixels in buffer = green), medium confidence (greater than 50% to 75% of pixels in buffer = yellow), and low confidence (less than 50% of pixels in buffer = red).
Each TED is also ranked in terms of its importance to corn production in the Eastern US, both by number and by percent. For example, in the first set of studies conducted by Nelson et al, there is a medium confidence level that the plurality TED is accurate for the study, and that TED is ranked eighteenth in terms of area in corn production in the Eastern US, representing 1.7% of corn production. Studies that were conducted in TEDs that do not fall within the top 75% of corn-producing areas, or that were conducted in Canada, are shown in the table in grey shading. The weighted mean values for delta yield in bushels per acre and delta yield in percentage for the entire data set are also shown at the bottom of the table.
Environmentally Smart Nitrogen (ESN®) is an enhanced efficiency nitrogen (N) fertilizer produced and distributed by Agrium. It is a polymer-coated, controlled-release urea product (often referred to as PCU or CRU), designed to protect against environmental N losses through leaching, volatilization, and denitrification. The polymer membrane encapsulating the urea allows water to diffuse into the granule, creating a urea solution that slowly diffuses into the soil over a longer period of time, so it is promoted as an ideal pre-plant, single-application N fertilizer. The slow-release increases the amount of N available to the crop when it needs it, but reduces the amount of N exposed to loss mechanisms during the time the polymer is protecting the urea. Based on these properties, ESN® is marketed to producers as a tool to increase N use efficiency (NUE) while decreasing the number of seasonal fertilizer applications needed, thus reducing supply and labor costs as well as soil compaction that results from multiple applications (Agrium Inc. 2014).
ESN® is for use with all crops for improving availability and reducing loss of soil nitrogen.
Farmers who wish to increase NUE by reducing nitrogen losses.
Varies based on volume.
ESN® is a polymer-coated, controlled-release urea fertilizer.
NutrientStar reviewers found no published research results from field scale strip trials.
Though only distributed wholesale in the U.S. since 2014, ESN® has been on the retail market since 2004 and has been studied in North America since the 1990s, providing almost two decades of research on its efficacy as an enhanced efficiency fertilizer. Grain protein results from an early laboratory study with barley suggested that coated urea allowed for a slower fertilizer release, providing a higher N supply in later growth stages (Zhang et al. 2000). Coated urea applied alone had the greatest reduction in potential N loss compared to non-coated urea and a mixture of both. Early field trials conducted on spring wheat across many sites in western Canada from 1998–2000 found similar grain yield and higher grain N content from seed-placed ESN® compared to side-banded urea applied at equivalent rates (Haderlein et al. 2001). These trials also demonstrated an average nitrogen use efficiency increase with ESN® of 4.2% across all sites, with a maximum NUE increase of 35%.
An intensive and extensive review of the literature was completed to assess the effectiveness of ESN® to increase yield of corn and wheat. All the research was completed on small plots. Typical plot dimensions were 5 feet wide by 60 feet long, and although plot sizes varied, none were greater than 1/5 of an acre.
Individual experiments have found both positive and negative yield impacts with ESN®, as the table of studies by TED regions shows, and the overall weighted average difference is not significantly different from zero.
Studies showed that where ESN® replaced urea in a seed-row fertilizer placement scenario yields were improved (due to the fertilizer coating which protected the seed from damage early on), but in studies where ESN® did not replace urea as an in-row fertilizer, greater wheat yield due to improvements in NUE is not well-supported with the data available.