Nitrification Inhibitors: For the next several weeks I will share data from on-farm research studies. Nitrification Inhibitors are best thought of as an insurance policy against loss of applied ammonium-based fertilizer due to excess rain in the first month or so after fertilization. For spring applications, some active ingredients have been proven by research to slow the conversion of ammonium to nitrate for at least two weeks, with a range of 1-6 weeks, depending on soil temperature. They are one tool (not a silver bullet), when used at right place and time, for aiding in nitrogen management. To summarize the research below, nitrification inhibitors are less likely to have a significant impact on increasing yield and reducing nitrate leaching in silt loam and silty clay loam soils as compared to sandy soils.
An ongoing study at UNL’s South Central Ag Lab (SCAL) near Clay Center is conducted on silt loam soils, common in the UBBNRD. The majority of the study at SCAL compared Spring pre-plant anhydrous vs. side-dress application with and without the use of nitrification inhibitor N-Serve® (nitrapyrin). A yield increase due to nitrapyrin applied pre-plant was observed in 6 of 28 years with a mean yield change of 2 bu/ac/year. Only 1 of 28 years was a yield increase observed when nitrapyrin was applied in season during side-dress application with a mean yield change of 0 bu/ac/year. In this study, they found delayed side-dress N with nitrapyrin could reduce plant N uptake and release N too late, thus it is not recommended to add an inhibitor to nitrogen applied in-season.
In 2019, two York Co. farmers compared spring anhydrous ammonia applications with and without the nitrification inhibitor (N-Serve®). At York location 1, 180 lbs N as anhydrous was applied on April 10, 2019 in ridge-till, silt-loam soil. At York location 2, 160 lbs N as anhydrous was applied on April 8, 2019 in no-till, silt-loam soil. These locations were around 4 miles apart and the previous crop in both was soybean. Soil samples were taken 2” off the anhydrous band down to three feet for both ammonium and nitrate concentrations at V7 growth stage. The results showed the nitrification inhibitor was still slowing the conversion of ammonium to nitrate in 1st foot at York 1 location (longer than would be anticipated for a spring-applied inhibitor treatment), but not at York 2. At both study locations, no yield difference occurred between the check and inhibitor treatments respectively (250 vs. 251 bu/ac at York 1 and 264 vs. 264 bu/ac at York 2).
In 2020, four farmers (3 in York Co. and one in Fillmore Co.) conducted on-farm research inhibitor studies. These studies were in partnership with the UBBNRD. Soil samples for ammonium and nitrate concentration were taken around 6 and 9 weeks post-application based on the protocol provided. Note: with these being inhibitor focused studies, future protocols will have soil tests taken closer to application. With farmers interested in what nitrogen distribution in the profile looks like in the late season, we will also sample then.
At York location 1, 150 lbs N as anhydrous was applied in the fall and spring with and without Centuro®. Soil tests in early May showed less total nitrogen in the third foot for the Spring anhydrous with Centuro® compared to Fall anhydrous with no inhibitor. There were no yield differences between treatments in 2020 (Fall and Spring check yielded 269 bu/ac, Fall with Centuro® 267 bu/ac, Spring with Centuro® 270 bu/ac). This study will continue. The other three locations had yields impacted by the July 9, 2020 wind event. At the Fillmore Co. location, 115 lbs spring applied 32% UAN with and without Instinct® II was compared. There was less nitrate and total nitrogen in the Instinct® II treatment at 2nd and 3rd foot vs. the check and there were no yield differences (both yielded 213 bu/ac). At the York 2 location, four products were compared (44 gal. spring applied 32% UAN as a check compared to the check plus either ammonium thiosulfate (ATS), Biovante™, or Instinct® II. The UAN+ Instinct® II had less nitrate and total nitrogen in the 3rd foot than the UAN+ Biovante™. The UAN+ATS treatment yielded significantly more than the check (215 bu/ac vs. 209 bu/ac) with no differences amongst the other treatments (212 bu/ac each). At the York 3 location, 45 gal spring applied 32% UAN was compared to a producer-developed concoction containing humic acid, sugar, and ATS. There was more nitrate, ammonium, and total nitrate in the inhibitor concoction than the check at the 3rd foot with no yield differences (220 bu/ac check vs. 221 bu/ac inhibitor concoction). These and other Nebraska on-farm research studies will be presented Feb. 25-26 both virtually and in-person. You can learn more and register here: https://go.unl.edu/h83j.
This week begins Nebraska Extension’s On-Farm Research Update meetings. Over 100 studies were conducted in 2019! Each meeting runs from 9 a.m.-4 p.m. (registration at 8:30 a.m.). Meal is included and there’s no cost thanks to our partnerships with Nebraska Corn, Soybean, and Dry Bean Boards and Growers’ Associations. Please pre-register at: firstname.lastname@example.org or 402-624-8030. Meetings are: Feb. 18 at Holiday Inn Express in Beatrice, Feb. 19 near Mead at ENREC, Feb. 20 in Norfolk at the Extension Office, Feb. 26 in Kearney at the Extension Office, and Feb. 28 in York at the Holthus Convention Center. At the meetings, you will receive a book of all the 2019 studies and hear from the farmers who conducted the studies if they are present at that specific location. What’s powerful about that to me is that you get to hear from your peers and the discussion and questions are greater. At all locations except for York, all the studies in the book will be shared. New this year to only the York location, only the cover crop on-farm research studies will be shared followed by outside speakers sharing about cover crop/soil health topics. That meeting also qualifies for UBBNRD nitrogen credits.
On-Farm research in Nebraska has occurred the past three decades. Growers partner with Extension and sometimes other government agencies and ag industry to test questions on their own farms using their own equipment benefiting many with the information. We often don’t have funding to do these studies. Thus, I’m extra grateful for our cooperating growers to research products and production practices that may not happen otherwise!
Sometimes, it’s best to hear from the farmers themselves regarding why they conduct on-farm research. The following YouTube video highlights area farmers David and Doug Cast of Beaver Crossing and Ken Herz of Lawrence:
Three York County farmers were also featured in a CropWatch article sharing their on-farm research experiences. Ron Makovicka and Jerry Stahr have conducted on-farm research since the beginning while Jay Goertzen was a first year participant. “Anytime you can get information, it’s very valuable. You can always learn something,” Stahr said. Goerzten shared, “There’s good support provided to help set up a research plot, help you with the follow through, and collecting data in-season.” All shared there was value in trying studies on your own farm with Makovicka emphasizing, “Go for it!”
This year, Makovicka and Stahr worked with me to compare areas with and without the nitrification inhibitor (N-Serve®) with their spring anhydrous ammonia applications. Nitrification inhibitors may reduce the rate at which ammonium is converted to nitrate thus helping reduce N losses through denitrification and leaching. Stahr applied 160 lbs N as anhydrous on April 8, 2019 in no-till, silt-loam soil. Makovicka applied 180 lbs N as anhydrous on April 10, 2019 in ridge-till, silt-loam soil. These locations were around 4 miles apart and the previous crop in both was soybean. At both study locations, no yield difference occurred between the check and inhibitor treatments. Soil samples were taken 2” off the anhydrous band down to three feet for both ammonium and nitrate concentrations at V7 growth stage. The results showed the nitrification inhibitor was working to slow the conversion of ammonium to nitrate in Makovicka’s field but not Stahr’s. We don’t have a good explanation for this. However, the results are consistent with other University studies conducted in silt loam soils.
Those are two examples of on-farm research studies. If you’re interested in trying a study for 2020, please contact your local Extension Educator. We work with you to set up your study in a scientifically valid way to work with your equipment. There’s also an opportunity to obtain up to $300 reimbursement for water-quality related studies through the UBBNRD (there is a short application form for that through the NRD). Please also save Mar. 2 from 9-Noon for an on-farm research ‘brainstorming’ meeting at the 4-H Building in York. I’ll share more on that and other study results next week.
*I’m grateful to Dr. Richard Ferguson, former Extension Soil Fertility Specialist, for reviewing this article; Dr. Charlie Wortmann, Extension Soil Fertility Specialist, for sharing research-based studies with me; and Glen Slater, SCAL Research Technician, for sharing details of the SCAL study mentioned below.
Nitrification Inhibitors: Two weeks ago, my column included a general overview regarding nitrogen losses in addition to general summary statements based on research. Nitrification inhibitors are best thought of as an insurance policy against loss of applied ammonium-based fertilizer due to excess rain in the first month or so after fertilization. Dr. Richard Ferguson, former Extension Soil Fertility Specialist, and his team have conducted much research regarding the use of nitrification inhibitors over time. Much effort has occurred in sandier soils within the Central Platte NRD. However, an ongoing study at UNL’s South Central Ag Lab (SCAL) near Clay Center is conducted on silt loam soils which are more common in the UBBNRD. Twenty-eight years of this study are summarized here. The majority of the study at SCAL compared Spring pre-plant anhydrous vs. side-dress application with and without the use of nitrification inhibitor N-Serve (nitrapyrin). This product was the product available back in the 90’s. The study actually began by comparing 2 different in-season side-dress applications before switching to pre-plant vs. side-dress in the early 2000’s. Soil samples for nitrate and ammonium content were taken when funding was available. In talking with Dr. Charlie Wortmann, UNL Extension Soil Fertility Specialist, he mentioned that they found yield to be correlated to amount of nitrogen in the soil. A yield increase due to nitrapyrin applied pre-plant was observed in 6 of 28 years with a mean yield change of 2 bu/ac/year. Only 1 of 28 years was a yield increase observed when nitrapyrin was applied in season during side-dress application with a mean yield change of 0 bu/ac/year. In this study, they found that delayed side-dress N with nitrapyrin could reduce plant N uptake. A detailed analysis of nitrapyrin effects on N uptake and soil accumulation from early years of this study can be found in Ferguson et. al (1991). The duration of inhibitor efficacy was measured in other studies where it was found a nitrification inhibitor such as nitrapyrin to last around two weeks with Spring applications. They’ve seen it last as little as 1 week to as long as 6 weeks depending on soil temperatures and moisture. The use of inhibitors is not advised in season as research showed they can release N too slowly for the crop demand resulting in yield loss and/or resulting in increased leaching of nitrogen when it was released too late in the growing season for crop uptake. In general, the research is more supportive for nitrification inhibitor use in sandy soils vs. heavier textured soils; yield benefit to a nitrification inhibitor may be none to a few bushels/acre for silt loam or silty clay loam soils.
In-Season Applications of Nitrogen: In-season application means the nitrogen is applied when the crop is actively growing and utilizing it, greatly reducing potential for loss. Recent on-farm research studies compared side-dress applications using either the UNL equation/Maize N model or industry models such as Climate Field View. In all these studies, the recommended rate was compared to rates that were at least 30 pounds over and under the recommended rate. Some of the studies went as high as +/- 50 lbs/acre compared to recommended rate. I’ve compiled these results in a table at https://jenreesources.com/2019/04/14/jenrees-4-14-19/. Take homes: In none of the studies did the addition of 30-50 lbs N/ac above the recommended rate increase the yield statistically. A few of these studies also compared side-dress applications vs. pre-plant alone. One situation resulted in a statistically lower yield with pre-plant alone while the other two resulted in no yield differences. Many of you have most likely heard of Project Sense in which a grower’s nitrogen application was compared to 75 lbs pre-plant + variable rate in-season application using sensing technology. This project was an on-farm research partnership with Nebraska Extension, Nebraska Corn Board and Corn Growers, and numerous NRDs including UBBNRD. From 2015-2017, 48 site-comparisons were conducted. The results showed 28.7 lbs less nitrogen was applied using the Project Sense method with a loss of 1.4 bu/ac in yield, and greater profitability of $7.24/ac. All of these results were statistically significant at the 95% level.
To reduce the risk of leaching or denitrification, consider applying the majority of nitrogen close to when crop demand is high with more nitrogen applied during the growing season vs. pre-plant. Also for consideration is the fact that farm operations differ in equipment and labor and growing seasons like 2019 present additional challenges, including for nutrient management.