Nitrogen Source and Rate Trial in Western Pennsylvania

Whether it is hay or pasture, nitrogen is one of the most limited nutrients to perennial grass systems and will almost always result in increased growth and production. However, as stated in the 4Rs of nutrient management, the questions are: What is the right source, the right rate, the right place, and the right time? In the mind of producers, maybe one more R should be the right price. A small on-farm plot study in Washington County examined these questions and their practical implications for producers, including cost analysis comparing forage tonnage and quality.  

What is being tested and how?

Sources and rates are assessed on twelve 22 x 75-foot plots. Applied sources include urea and polymer-coated nitrogen. In most agricultural settings, urea is the standard nitrogen source with an analysis of 46-0-0. One drawback to this product is that urea nitrogen can be lost to volatilization if not applied before rain or as a stabilized product. Polymer-coated nitrogen is designed to be a slow-release product with resistance to volatilization and provides nitrogen throughout the season as the polymer coating slowly breaks down. The product used in this trial has an analysis of 44-0-0. When using a polymer-coated nitrogen product, the manufacturer recommends applying 20 to 30% of the total recommended nitrogen as a faster-releasing, more available product like urea or ammonium sulfate, and 70 to 80% as polymer-coated. For example, we applied 100 nitrogen units, meaning 70 units came from the polymer-coated product, while 30 units came from uncoated urea. 

1- Plots received an additional 3 lbs. of N with the MAP application
2- Recommended phosphorus was 20 lbs./ac, but to avoid it as a limiting factor, it was applied at 30 lbs./ac
3- Recommended potassium was 170 lbs./ac, but to avoid it as a limiting factor, it was applied at 200 lbs./ac. These applications were split- 125 lbs at green-up and 75 lbs after the first cut. 

Five treatments are being tested (Table 1). The fallow treatment is an area with no fertilizer or manure history. This will be used as a benchmark for tonnage and forage quality in the economic comparison. The control treatment received phosphorus and potassium, but no nitrogen. The single treatment received 50 nitrogen units, as urea, applied at green-up. The split treatment received 50 units of nitrogen as urea at green-up, followed by 25 units after each cutting. This comparison will provide information on increased dry matter and production in a more intensive nitrogen management system. The ESN and urea received 100 units of nitrogen,  as a slow-release polymer (75 units) and urea (25 units), but all at green-up. This will allow for comparison between 100 units applied as multiple applications and the single application as slow release. There were three replicates of each treatment. 

A soil test was taken from the trial area to ensure that all treatments would perform at or near optimum. Prior to fertilization, phosphorus and potassium were 40 and 67 ppm, respectively. This report was then used to treat the area for phosphorus and potassium deficiencies to avoid them being limiting factors.

Notes and Observations

Green-up to First Harvest

• Between January 1 and March 25, 2024, this field had received 18.30" of rain and had 478 growing degree days (GDDs). That made it 29% wetter and 95% warmer than the 10-year average.
• Fertilizers were applied on March 25, 2024. Within 12 hours, this field received approximately 0.6" of rain. We intentionally applied at this time to reduce volatilization and increase fertilizer capture. 
• Early on, differences became very apparent between nitrogen and non-nitrogen treated plots. Differences were not only in color, but also in density and speciation. 
  • Control and fallow plots were thinner and more yellow, while the nitrogen-treated plots were much more leafy and dense with a greener color. 
  • In the May 3 image below, there is a clear difference in forage speciation. The control plot is dominated by vernal grass, bluegrass, and other less desirable species. The ESN and urea-treated plot has much more orchardgrass and fescue present within the stand.

• • In the May 13 image below, you can see the different species in head. The image on the left is almost completely headed and averages about 20" in height. The image on the right is about 25" in height and only partially headed. This difference in head timing is due largely to forage species expression and additional nitrogen, allowing the forage to stay vegetative longer. 

First to Second Harvest

• Depending on the treatment, the plots produce between 400 and 1,400 lbs. of dry matter (DM) per acre. With this inconsistency, it was decided to clip the tops of the grasses, fertilize, and hope for a better third cutting. There was concern about thatch and moldy forage being present for the third cut, so for the contest of height, view the images below. 
  • At second harvest, the control, receiving no additional nitrogen, produced 400 lbs. of DM per acre, while the ESN and urea applied treatment produced 1,200 lbs. DM. It is evident that even in unfavorable conditions, forages in optimum fertility situations can continue to produce. 

• • Between May 20 and July 15, this site received 2.25" of rain and had 1,207 GDD, making it significantly drier and warmer than the 10-year average. As shown in the image below, forage without adequate fertility did not produce as well during adverse conditions.

Second to Third Harvest

• Rain and cooler temperatures returned between July 15 and September 17, in turn allowing for a better third harvest. 
  • As shown in the image below, within 21 days of clipping, there was very little thatch left on the plots, and the plants were beginning to green up again. Again, with such low forage density, we were only clipping the tops of forages and weeds, reducing stands to a height of approximately 4".

• Third harvest samples were collected for DM only, and not analyzed for forage quality. Since tonnage was so low, 800 to 1,800 lbs. DM/ acre, and the producer had an adequate stored hay supply, the third cutting was not harvested.  

Harvest and Forage Analysis

Harvest sampling was taken using a hedge trimmer and a 0.25 m² quadrant. The quadrant served as a guide for the hedge trimmer so the sample could be collected in its entire length and volume. The quadrant was designed to be 2" tall, so when the hedge trimmer guided across, this ensured an even 3.25" cutting height. Two samples were collected from each treatment to give a total sampling area of 0.5 m². Part of the sample was air-dried, weighed, processed through a Koster Tester, and reweighed for dry matter calculations. A smaller sub-sample was air-dried and sent to Cumberland Valley Analytical Services Lab for forage quality analysis. 

Over the first and second harvests, plots treated with nitrogen yielded more forage than plots that were not treated with nitrogen. As shown in Table 2, all nitrogen-treated averages were more than 2 tons DM per acre on first harvest, while the control was 1.4 tons. As reported in the observations section, between May and July, this site received little rain and lots of heat, leading to a diminished second cut. However, the nitrogen-treated plots still yielded more forage than those that were untreated. Between July and September, the weather improved and yields rebounded, resulting in split-applied and ESN and urea treatments yielding significantly more during the third cutting. 

Crude protein and total digestible nutrients, TDN, are also measured and compared. As shown in Table 2, the ESN and urea treatments showed significantly higher protein when compared to other treatments. Total digestible nutrients were not significantly different for any treatments. This is believed to be due to a consistent harvest time, rather than harvesting individual treatments at their physiological maturity.  

1- Harvest 1 date was May 20, 2024
2- Harvest 2 date was July 15, 2024
3- Harvest 3 date was September 17, 2024
4- Multiple samples were collected, but there was only one replicate, so statistics could not be compared. 

What did it cost? 

For cost analysis in Table 3 below, we compare acres needed, price of production, cost to match production, and loss/gain. The total harvest was reflective of Table 2, and the total tons of DM harvested per acre. Area to match is a ratio of the most productive treatment compared to the other treatments; this allows us to compare apples and apples, not apples and oranges. For example, the most productive treatments were split and ESN and urea, each producing 3.8 tons/acre. If we compare that to the single urea treatment, which produced 2.8 tons/acre, we need 1.4 acres of single treatment production to meet the production of split or ESN and urea treatment (3.8 divided by 2.8 = 1.4 acres). With this number, we can start comparing the profit and loss. Knowing that we would need 1.4 acres of single to match the split application treatment, we multiply 1.4 by the single treatment price of production. Price of production is a combination of custom survey rates for mowing, tedding, raking, baling, and fertilizer applications, and 2024 fertilizer prices. We now have a cost of match, which gets us to apples and apples. Cost of Match is the price of production multiplied by the area to match. Loss/gain is the subtraction of the cheapest cost of the match from other treatments. 

After analysis, the split treatment has the highest price of production at $395 an acre, with ESN and urea right behind at $391. However, because these management practices produce significantly more forage than the other treatments, the price is split over more tonnage, resulting in a lower cost per acre. A few things to consider: 

• Nitrogen is often the most limiting nutrient in a forage system, and it can cost a lot. In the case of the control or the single treatments, fertilizer prices are high to apply phosphorus and potassium, but without the additional nitrogen, we are not getting the needed tonnage to offset those prices. Think of it as P and K will coil the spring, but without N, there is nothing to release it and take advantage of all that stored energy. 
• The split treatment has a net loss of $4 an acre when compared to ESN and urea. Even though the split treatment is more expensive, it provides the greatest flexibility. If you have equipment, personal, or weather-related issues, you have the ability to skip a treatment and save that money for another time. Yield will reduce, but you are getting a more reactive approach to nitrogen management. On the other hand, ESN and urea are a once-a-year application, meaning during the summer, you could focus on hay making, spraying or fertilizing other crops, not top dressing the hay ground with nitrogen. 
• The fallow treatment was only $15 less over almost 3 acres to produce the same volume of hay. If taking a no-fertilizer approach, consider the difference in forage quality from Table 2 and the unnecessary wear and tear on equipment. By fertilizing and managing forage ground better, you could potentially reduce supplemental animal feeds and reduce your needed acreage by 1/3.

What's next?

In 2025, we will repeat this project. We will soil test treatment plots and address any changes to pH and fertility. Optimistically, we will get more consistent, historical weather for the second year of data. We will continue to update the economics and data as we have new things to report. 

Thank yous, and Collaborations: 

Special thanks to the Washington County Conservation District Staff and their Board. Also, thank you to the Midla's and Flat Stone Lick Farm for hosting the trial.