Nitrogen timing saves, creates green

Fertilizer prices are extremely high at this time. How do we economically stimulate pasture growth throughout the growing season?

In general, nitrogen has the greatest potential to influence pasture production, or dry matter production.

The economics of nitrogen application can be influenced by many factors, such as legume content, temperature, soil moisture content, grass species, timing of application, form of nitrogen applied, organic matter content and phosphorus and potassium levels, to name a few.

Economical

When is it economical to use nitrogen on a pasture? The answer is, when you need more forage and when the legume content of the pasture sward is less than 35 percent.

When is the best time to apply nitrogen to a pasture? Plants will use available nitrogen when they begin actively growing. We know that cool season grass pastures will produce 60-70 percent of their total annual production in the spring with fall being the next major bump in growth.

Therefore, consider these time periods when making an application of nitrogen to grass pastures.

How much nitrogen do I apply? I’ll answer this question with another: how valuable is the forage you are producing?

Timing

For example: Let’s break the growing season and timing of nitrogen applications into three periods: May, June and August.

Applying nitrogen at each of these time periods will result in a different yield potential and therefore a different level of economic efficiency.

If we expect a fescue/orchardgrass pasture with 10 percent legume to yield the following:

• 20 pounds of dry matter per pound of nitrogen applied — in May

• 10 pounds of dry matter per pound of nitrogen applied — in June

• 14 pounds of dry matter per pound of nitrogen applied — in August

(These yield estimates will vary.)

If urea is $500 per ton and we value comparable hay at $100 per ton, how do the economics work out?

• $500 divided by 920 pounds of nitrogen in a ton of urea equals 54 cents per pound of nitrogen.

We will use 50 units of actual nitrogen.

• 50 pounds times 54 cents equals $27 per acre to apply 50 units of nitrogen, not including spreading.

Based on our example here:
• The May application could result in 20 pounds of dry matter times 50 units of nitrogen equals 1,000 pounds of dry matter.

• The June application will result in 10 pounds of dry matter times 50 units of nitrogen equals 500 pounds of dry matter.
• The August application will result in 14 pounds of dry matter times 50 units of nitrogen equals 700 pounds of dry matter.

Forage value

We said comparable hay was worth $100 per ton and is 87 percent dry matter. Therefore, our value of this forage is: $100 divided by 87 cents equals $114.94 per ton of dry matter or 5.7 cents per pound of dry matter.

How do the economics compare on these three different applications?

• The May fertilization resulted in 1,000 pounds dry matter times $.057 per pounds equals $57 less $27 cost of nitrogen equals $30.
• The June fertilization resulted in 500 pounds dry matter times $.057 per pounds equals $28.50 less $27 cost of nitrogen equals $1.50.
• The August fertilization resulted in 700 pounds dry matter times $.057 per pounds equals $39.90 less $27 cost of nitrogen equals $12.90.
If you need more pasture growth and can use nitrogen, consider using it in 50-unit increments of actual nitrogen and during periods of when you need forage growth.

For more information on pasture fertility management ask your local Extension office for a copy of Fertility Management of Meadows, ANR-5-99.

About the Author

The author is an Ohio State University Extension Agriculture and Natural Resources Educator in Guernsey County. More Stories by Clif Little

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