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Nitrogen Rate and Source Effects on Grass Hay Yield and Quality

In Pennsylvania, nitrogen is often the most limiting resource in grass hay production, leading to reduced production quantity and quality. With improved nitrogen management, producers could increase yields by as much as 75%, while also significantly impacting production costs.

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Updated:

December 16, 2025

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The left plot received no fertilizer nitrogen, while the right was provided with 50 units of N at green-up, resulting in a significant increase in crop density, height, and appearance. Image Credit: J. Brackenrich, Penn State Extension.

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Investigator(s)

Justin Brackenrich, Extension Educator
Guojie Wang, Penn State Forage Specialist

Background

In Pennsylvania, nitrogen is often the most limiting resource in grass hay production. Better nitrogen management not only can increase forage yield but also may increase forage quality. For better nitrogen management, producers or applicators must first decide the source and rate of nitrogen that best suits their operation.

Objective

The objective of this trial was to determine if producers could produce more grass forage on less acreage, more economically, with improved nitrogen management.

Methods

To test this objective, two nitrogen sources (urea and ESN, a polymerized, slow-release nitrogen product) were applied at various rates, resulting in four treatments (Table 1), each replicated three times. All tested plots received lime, phosphorus, and potassium as recommended by soil test results. Dry matter yield and forage quality were analyzed at first and second harvests, but only dry matter yield was analyzed at the third harvest. While fertilizer prices were known, custom farm equipment rates were used to determine the equipment costs for all farm activities. Economic analysis was used to determine the production price per acre, the cost per ton of forage, and the net profit/acre.

Table 1. Treatments Used to Evaluate Nitrogen Applications
Treatment	Nitrogen Source	Nitrogen Rate (units N/acre total)	Phosphorus Rate (lbs/acre)	Potassium Rate (lbs/acre)
Control	n/a	n/a	30	200
Single¹	Urea	50	30	200
Split²	Urea	100	30	200
Stabilized³	ESN and urea	100	30	200

¹ Indicates a single application of 109 lbs/acre urea (46% N) at green-up.
² Indicates split applications of urea: 109 lbs/acre at green-up and another 54 lbs/acre after each harvest.
³ Indicates an application of 170 lbs/acre ESN (44% N) and 54 lbs/acre urea at green-up.

Results

Since their establishment in 2024, plots were evaluated weekly, from April through October, for forage height and density. Forage and weed speciation were also noted during this evaluation. Plots were to be harvested when forage reached mid- to late heading; however, drier periods in both 2024 and 2025 resulted in growing conditions that were less than ideal. Therefore, sampling was not based on any physiological or day schedule but rather on a visual assessment and the amount of forage present. Harvest dates were May 20, July 15, and September 17, 2024, and June 6, July 21, and October 6, 2025.

On a per-acre basis, fertilizer and equipment costs were higher when nitrogen was applied. However, even during drought periods, the increased forage tonnage covered the costs of recommended amendments and provided an additional return on investment (Table 2). The control treatment yielded an average of 2.2 dry matter tons per acre per year, which is significantly less forage than the other treatments. The control had a lower production cost per acre; however, the reduced yield resulted in a higher production price per ton. While production costs between the single and polymerized treatments may not be substantial, the tons of dry matter produced were significantly higher on the polymerized treatment. Production costs were reduced by 8 to 21% when we compared nitrogen-applied treatments to the control.

Table 2. Forage Collection Results, 2024 and 2025
Treatment	Treatment cost¹ ($/acre)	Total dry matter² (ton/acre)	CP³	TDN³	RFV³	Production cost⁴ ($/ton)
Control	273	2.2a	12.1a	61.3	101	124
Single	331	2.9b	12.3a	61.5	106	114
Split	382	3.9c	12.8b	61.1	101	98
Polymerized	369	3.5c	13.9c	62.1	105	105

¹ Combination of fertilizer and equipment costs, average of 2024 and 2025.
² Combination of all harvests, average of 2024 and 2025.
³ Mean value of the second harvest, average of 2024 and 2025.
⁴ Production costs/acre divided by total dry matter/acre.

Forage crude protein increased with the split and polymerized treatments, compared to the single and control treatments. This finding confirms that a single nitrogen application in spring will have no significant impact on protein or plant nitrogen in the second harvest. Total digestible nutrients and relative feed value (RFV) did not differ significantly since these quantitative factors are largely influenced by harvest timing and all plots were harvested simultaneously.

Conclusion

Due to grass's high demand for nitrogen and the dynamic movement of nitrogen in soils, timely and suitable fertilizer applications are crucial for producing high-quality grass forage. Nitrogen management should be part of a program that maintains optimum pH and adequate levels of phosphorus and potassium. While nitrogen rates should be adjusted according to your yield goals, applying 100 units annually in a polymerized form in the spring or splitting the application throughout the year allows for both a cost-effective and environmentally efficient use of nitrogen throughout the growing season.