Forage Focus: Nitrogen Fertilization Of Pastures & Hay Fields

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For some this may be a little late but the question still remains what is the best way and time to fertilize pastures and hay fields. Many opt for spring fertilization but even once you decide when you are fertilizing how do you decide how much you should fertilize? Maybe you will base your fertilization rate on a soil test, a shot in the dark, or simply nitrogen fertilization but the question still remains what is the best method? Well obviously soil tests are the only real way to tell what you are working with so test even those pastures and hay fields to make sure you are getting the most out of them. Remember, no amount of nitrogen can make up for other nutrients that may be limited. Even with a soil test, however, there are still some decisions to be made on what you should do with your nitrogen fertilizer.

First off take a hard look at your pasture or hay field and see if there is any legume component in the field. If there is a significant amount of legumes (20-30 percent uniformly throughout the field) you probably don't want to fertilize with N. Legumes will produce nitrogen for your grasses and an addition of nitrogen fertilizer will favor the grasses and may lead to a decline in legumes in the pasture.

If you have grass fields that do not contain legumes you should think about the timing of your nitrogen fertilization. For grass hay it is typical to fertilize in the spring to obtain the highest yield possible. This practice has also been widely accepted when dealing with pastures; however you may want to look at your individual system prior to this action. If you already have a low enough stocking rate that it makes it hard to keep up with the spring flush of grasses you may want to hold off on the spring nitrogen as this will only add fuel to the fire.

Once these options have been taken into account you still should think about whether you have the ability to split your application of nitrogen for greater efficiency. For instance, the nitrogen recommendation for an orchardgrass stand that has an expected yield of 4 tons per acre is 200 lb/ac. If this is applied all at once that nitrogen has to stay in the field until all cuttings have been removed. A quick look at the nitrogen cycle will reveal that nitrogen escapes our systems very easily so it may not stay as long as we desire. One way we can manage this is to actually split the application based on how many cuttings we expect to take and it is even better if we can adjust the rate for the expected yield of the next harvest. For the same field we may decide we want to apply 100 lbs. in the spring and 100 lbs. after the first or maybe better yet the second cutting instead of the all 200 lbs. in the spring. Since cool season grasses are not very productive in the heat of the summer a lower rate of N is all that is needed. Obviously, the only limitation on this is the cost and hassle of multiple fertilizations if you do not own your own equipment.

One last thought should be given to the type of nitrogen fertilizer used. Urea (46-0-0) is the most commonly used nitrogen fertilizer for pastures; however it can have large losses due to a process called volatilization, especially in the heat of the summer. If urea is used try to apply it right before rain for maximum efficiency. Do not apply urea right after a rain because the losses will be greatest then. Another option could be ammonium sulfate (21-0-0-24). This product does not volatilize so all the nitrogen you apply will be plant available. Some of the limitation to this, however, may include price and the fact that you have to handle about twice the product for the same rate of nitrogen per acre.

Source: Jonathan Rotz, Doug Beegle, and Marvin Hall, Penn State Extension



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