Fertilize spring pastures with nitrogen

A few days ago the Athens County Grazing Council in southeast Ohio met for the first time this year.

The question came up about spring nitrogen fertilization on pastures.

There are several important factors to consider in arriving at a sound approach for nitrogen management in pastures.

Not one size fits all. To determine if spring nitrogen fertilization is a good choice in your situation, begin by answering the following:

“Do I really need to promote earlier growth, and is my animal stocking rate sufficient to utilize the extra boost in spring growth from the nitrogen?”

If you can answer yes to both questions, then a light nitrogen application on a portion of your pastures may be a very good choice.

Rates. Applying 40 to 50 pounds of actual nitrogen per acre in early spring (March in Ohio) can help get animals on pasture one to two weeks earlier than usual by stimulating early season grass growth.

Caution. A word of caution: Early spring nitrogen fertilization can easily result in excessive growth in May that is not efficiently utilized by livestock.

We often have too much grass in late spring, and adding nitrogen just amplifies this problem.

Besides having overly mature, low quality forage, shading at the base of grass plants reduces tiller number and development.

Fewer and weaker tillers will probably compromise forage production later in the summer.

Strategic application. If spring growth is usually plentiful in your operation and you aren’t desperate for earlier grazing, then delaying nitrogen application to early summer will provide a better return.

A mid-June application can increase forage production in July and on into August when pasture growth tends to slump.

An early August application should be considered for stimulating grass growth for stockpiled grazing in late autumn and winter.

Other considerations. Legume content of the pasture, soil organic matter content, phosphorus and potassium fertility status, and nitrogen cycling by animals are other important factors affecting nitrogen application needs in pastures.

If the pasture contains more than 35-40 percent legumes, nitrogen fertilizer is usually not cost-effective for spring and summer production.

Legumes fix atmospheric nitrogen, and a significant portion of this becomes available to the grass plants.

Soils with higher organic matter content will release more organic nitrogen to the forage, also reducing the need for nitrogen fertilizer

Nitrogen cycling. In a grazing system, animals recycle over 90 percent of the nitrogen they ingest.

Some nitrogen in feces and urine is lost and some of the organic nitrogen is released over time.

But the net result of animal recycling is to reducing the need for nitrogen fertilization compared with hay systems where manure is not returned to the field.

Of course, your grazing management will affect the distribution of the recycled nitrogen in the pasture.

Fertility response. A recent soil test will show if the pasture is lacking in phosphorus and potassium. Soils lacking these nutrients will be less responsive to nitrogen fertilization.

Unfortunately, there are no reliable soil tests for determining expected fertilizer nitrogen response in pastures.

Tetany caution. The hazard of grass tetany may be increased with early spring nitrogen fertilization and early grazing on lush pastures.

If problems have occurred with grass tetany in the past, supplement animals with magnesium.

(The author is an associate professor in the Department of Horticulture and Crop Science at Ohio State University. Questions and comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)

About the Author

The author is an associate professor in the Department of Horticulture and Crop Science at Ohio State University. More Stories by Mark Sulc

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