Journal of the NACAA
Volume 8, Issue 2 - December, 2015
Utilizing Urease Inhibitors With Urea To Stockpile Fescue
- Penrose, C., Associate Professor and Extension Educator, OSU Extension, Morgan Co.
McCutcheon, J., Associate Professor and Extension Educator, OSU Extension, Morrow Co.
Landefeld, M., Assistant Professor and Extension Educator, OSU Extension, Monroe Co.
Stockpiling fescue with urea fertilizer to extend the grazing season is a viable option for many producers. One of the problems with this practice is the possibility of inadequate rainfall and the volatilization of the urea. The addition of urease inhibitors such as Agrotain® may reduce volatilization. In a 2014 replicated study, urea (46 pounds of nitrogen per acre) with Agrotain® (four qt./acre) was compared with urea only (46 pounds of nitrogen per acre), and no treatment (control). With less than three days after treatment before a significant rainfall, results indicated a trend toward higher yields with the treatments (P≤0.10); significant increases (P≤0.05) in crude protein with the treatments; no significant differences between the treatments and the control; and no significant differences in ADF between the three treatments.
One of the greatest expenses for beef and sheep producers is the cost of stored feed. One way to lower these costs is to field stockpile forages for fall and winter grazing. Stockpiling means to make the last harvest by clipping or grazing of a hay field or pasture and then let it grow for grazing later; in this situation, the fall or winter.
Tall fescue (Schedonorus orundinaceus, Schreb.) is the most desirable grass to stockpile for late fall and winter grazing. During the fall, this grass produces higher yields of stockpiled forage of superior quality compared to most other temperate grasses. The fall saved forage is very palatable and high in digestibility (high in soluble sugars). Forage quality losses from leaf deterioration after frost are lower for tall fescue compared to most other forages. Often, tall fescue does not go completely dormant during lower temperatures; thus, there may be growth in late fall and winter if temperatures remain above 400F for a few consecutive days. Tall fescue forms a strong sod that is tolerant of trampling damage, which is common on wet pastured soils during the winter. Winter grazing has minimal influence on yield or quality of this grass the following season.
Tall fescue has a bad reputation among many producers because animals do not graze it readily during the summer months. Some of this reduced summer palatability is associated with the presence of a fungus in the plant (endophyte). The fungal endophyte produces alkaloids that are toxic to animals and cause various animal health problems. Many existing fescue stands are endophyte-infected, but the level of infection varies considerably. Animal health problems associated with endophyte-infected stands occur primarily in the summer when animals are under heat stress. Adverse health effects are less common on infected fescue pastures in the fall and winter. The toxin produced by the fungal endophyte is less concentrated in leaf tissue than in the seedheads and stems, so the amount of toxin consumed in the fall is less than in the spring and early summer. The cooler temperatures in the fall and winter reduce the heat stress problems associated with endophyte-infected fescue (Penrose, Bartholomew & Sulc, 1994).
Studies have demonstrated that one way to improve the quality and yield of fescue is to apply nitrogen fertilizer (N) when stockpiling is initiated. Urea is the most common form of N used for stockpiling since ammonium nitrate is not readily available to producers. The biggest risk, when applying urea, is not receiving adequate rainfall and volatilizing before it reacts with the soil. Volatilization losses may be reduced if a urease inhibitor is used with the urea. The most common urease inhibitor is NBPT (N-(n-butyl) thiophosphoric triamide) sold under the trade name Agrotain® (Agrotain International) (Schwab, & Murdock, 2010). In Southeast Ohio, studies and demonstrations have been conducted to evaluate quality and quantity of stockpiling cool season grasses such as fescue. The objective of this study was to determine if the addition of a urease inhibitor can increase yield and quality of stockpiled fescue compared to urea alone or no additional nitrogen.
The trial was located at the Ohio Agriculture Research and Development Center, Eastern Ohio Research Station in Noble County, Ohio. The soil is a Vandalia-Guernsey silt clay (USDA Web Soil Survey, 2015). The treatments included no urea and no urease inhibitor (control), 100 lb./acre (46 lb. of N), and 100 lb. of urea/acre with four qt. of Agrotain®/ton of urea. The treatments were replicated four times using complete randomized block design. Each plot was six feet by twenty feet. The site was a predominately fescue pasture. The soil was tested prior to beginning the trial which was initiated on August 8, 2014. The p.H. was 7.3; P, 51 ppm; K, 90 ppm; Ca 4185 ppm; and Mg 406 ppm. At the beginning of the trial, the plots were clipped to a height of six inches.
The plots were harvested on December 3, 2014 to a height of four inches above ground level utilizing 2’ x 2’ subsamples from each plot. Each subsample was weighed fresh, and then forced air dried at 350 degrees for 24 hours until the weight of each sample was stable. Each of the 12 samples was quality tested for Acid Detergent Fiber (ADF) and Crude Protein (CP). Statistics were run using SAS (Carey, NC) Proc Mixed with PDIFF for mean separation.
Results and Discussion
Dry matter (DM) yields averaged 2369 pounds per acre for the plots with no N, 3147 pounds for the plots with 46 pounds of N applied as urea, and 3210 pounds for the plots with 46 pounds of N applied as urea with Agrotain®. While there is no significant difference in the treatments (P≤0.05), there was a trend (P≤0.1) of higher yields with the treatments (table 1).
There was a significant difference (P≤0.05) in crude protein (CP) with urea and urea with Agrotain® compared to the control plots. CP averaged 6.77% for the plots with no urea; 8.53% for the plots with 100 lb. urea/acre and 8.32% for the plots with urea and Agrotain®. There were no significant differences in ADF with the control and treatments. While there is no significant difference between the Agrotain® treated urea plots and the urea only plots, this and other studies such as Overdahl, Rehm & Meredith (2015) indicated that urea and urea with Agrotain® can improve yield and quality compared to the control of no additional N.
|Control (no N or N with urease Inhibitor)
|46 pounds of N in the form of urea
|46 pounds of N in the form of urea plus urease inhibitor
Table 1. Results of ADF, CP and Yield of Stockpiled Fescue. *Means with the same letter are not significantly different (P<0.05).
Stockpiling began on August 8, 2014 and the treatments were applied. On August 11, the site received over a half an inch of rainfall (0.59 in.), with more rain on August 12 (0.56 in.). Previous research indicated that a half an inch of rainfall within 48 hours of application would help prevent the urea from volatizing back into the atmosphere (Overdahl, Rehm & Meredith, 2015). It was the intent of this study to have no rainfall for an extended period of time (one to two weeks) to show significant differences between the treatments.
One of the biggest problems with using urea to stockpile cool season grasses is the uncertainty of a timely, adequate rain in the late summer. In this study, we had rain within 72 hours of the initiation of the study which likely limited the volatilization of the urea only treatments as compared to no rainfall for a longer period of time. This is likely the reason there were no significant differences in quality and yield in the plots with urea only compared to the urea with Agrotain® plots.
In 2013, this project was conducted where stockpiling was initiated on August 5. This was not reported due to unplanned grazing prior to the final harvest of the plots. There was not a soaking rain for seventeen days (there were three separate days of .05-.15 in. rain) then there was 1.5 in. of rain on August 22. On October 14, samples were harvested from one set of plots prior to an unplanned grazing, and the plot with no N had 2003 pounds of DM per acre, the plot with 46 pounds N in the form of urea had 2904 pounds of DM per acre, and the plot with 46 pounds of N in the form of urea with Agrotain®; had 4141 pounds of DM per acre. The one set of results indicated a higher yield for the plots with urea and Agrotain®, compared with urea alone and no urea.
Stockpiling cool season grasses and in particular fescue can reduce the need for stored forages and in many cases it is higher quality than the hay we make. Adding nitrogen, approximately 50 pounds per acre when stockpiling is initiated can increase yields and quality. In this study, the plots with nitrogen added had increased CP levels nearly four months after application that would reduce or eliminate the need for supplemental protein in the diets for some livestock depending on their stage of production. Agrotain® may be a good option if there is any doubt about rainfall after applying urea. Several cattle producers in our area have tried it with success and research from University of Kentucky confirms it improves yields. Research will continue to determine how the addition of a urease inhibitor will impact yield and quality during extended periods of no rain.
Overdahl, C.,Rehm, G., & Meredith, H. (2015). Nutrient Management: Fertilizer Urea. Retrieved from: http://www.extension.umn.edu/agriculture/nutrient-management/nitrogen/fertilizer-urea/
Penrose, C., Bartholomew, H., & Sulc, R. (1994). Stockpiling Fescue for Winter Grazing. Retrieved from: http://ohioline.osu.edu/agf-fact/0023.html
Schwab, G., & Murdock, L., (2010). Nitrogen Transformation Inhibitors and Controlled Release Urea. Retrieved from: http://www2.ca.uky.edu/agc/pubs/agr/agr185/agr185.pdf
United States Department of Agriculture, Natural Resource Conservation Service (2015). Web Soil Survey. Retrieved from websoilsurvey.nrcs.usda.gov/