Western Pennsylvania Nitrogen Trial on Grass Hay

May 09, 2024

By Justin Brackenrich

Nitrogen is essential to cool-season forage production, but what is the right rate and source? A small trial is looking at just this question.

Whether it is hay or pasture, nitrogen is one of the most essential 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? A small plot study in Washington County examines these questions and their practical implications for producers.

The practical question being investigated with this trial is whether producers can use different nitrogen sources and rates to increase forage tonnage. Literature, research, and years of observation tell us this answer is yes. With improved nitrogen management, farmers could have more forages for winter feeding or sales, reduced wear and tear on equipment, and/or reduced land rent expenses. With the rising cost of operating and inputs, what is important is whether it pays to prove your nitrogen management.

We are looking at whether this "pays" from a couple of different angles: 

  • If hay is valued at $X a ton and costs $Y to purchase and apply additional nitrogen, operations need at least $Z to make this practice pencil out. 
  • It will likely improve forage quality to purchase and apply $Y additional nitrogen. Improved forage quality can increase animal performance and reduce the need for supplemental feeds. Additional nitrogen application must reduce implementation by $X or increase animal performance by $Z to make this practice pencil out.

What is being tested and how?

Twelve 22 x 75-foot plots assess the effect of different nitrogen fertilizers applied at different rates. Applied sources include urea and polymer-coated nitrogen. In most agriculture 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 recommended nitrogen as a faster-releasing, more available product like urea or ammonium sulfate. For example, if you would like to apply 100 nitrogen units, 70 units should come from polymer coated, while 30 should come from urea or ammonium sulfate.

The timing comparison will include different rates for green-up and split applications after cutting. One treatment is 50 nitrogen units, as urea, applied at green-up. Another is 50 nitrogen units 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 third treatment is 100 units of N as a slow-release polymer (75 units) and urea (25 units). This will allow for comparison between 100 units applied as multiple applications and the single application as slow release. There are three replicates of the following four treatments. 

  1. Control: No nitrogen added.
  2. 50 units of urea N at green-up (109 lbs urea/ac). 
  3. 50 units of urea N at green-up (109 lbs urea/ac), followed by 25 units of urea N after each cutting (54 lbs urea/ac).
  4. 100 units of N at green-up as 75 units of polymer-coated nitrogen and 25 units of urea N (170 lbs of polymer-coated and 54 lbs urea / ac).

A soil test was taken from the trial area to ensure that all treatments would perform at or near optimum. This report was then used to treat the area for phosphorous and potassium deficiencies.

  • Soil pH - 6.3
  • Magnesium - 133 ppm
  • Phosphorus - 40 ppm
  • Potassium - 67 ppm

Penn State Ag Analytical Services lab soil pH reports for southwest PA showed that in 2022-2023, of 488 soil tests, 31% were between 6.1 and 6.5 pH. For this reason and to make the trial more applicable to area producers, pH was not modified, even though it called for 2,000 lbs of CaCO3/acre. Phosphorus fertilizer was applied at an equivalent rate of 50 lbs/acre. The potassium needed was 220 lbs/acre. To avoid luxury consumption and over-application, 60% of the potassium fertilizer was applied at green-up, and the remaining 40% will be applied after the first harvest.

Notes and Observations:

Two things to consider now and eventually when we report economics will be soil fertility and harvest management. Let’s start with fertility. Plants will only grow to the extent of the most limiting nutrient. In our situation, that would have been potassium. Before considering a more management-intensive nitrogen system, ensure plant growth will not be limited by other nutrients or soil pH. Next is harvest management. Harvest management is the number one factor controlling forage quality. If we harvest this hay too late, when it is rank and heady, it may have more protein because of additional nitrogen in the soil, but the quality and digestibility will still be low. Somewhere between boot and early heading will provide the best forage quality and quantity ratio. Since this forage will be for beef cattle, we are targeting early heading for harvest. 

Since January 1, this field has received 18.30" of rain and has had 478 GGDs. That makes it 29% wetter and 95% warmer than the 10-year average. 

Fertilizers were applied on March 25. Within 12 hours, this field received approximately 0.6" of rain. We intentionally applied at this time to reduce volatilization and increase fertilizer capture. 

What's next?

Articles will be written over the next few months, providing updates on harvest, fertilizer applications, forage analysis, and concluding with our economic analysis. A field day is also being planned at the farm in Washington County. We will look at these plots in more detail and explore the management and harvest of warm-season annuals grown on the operation. More information for the field day will be provided in the next article. You can also check our Field and Forage Crop Facebook page for video updates.

Source : psu.edu