Management on Pasture
Sid Bosworth, Extension Associate Professor,
Department of Plant and Soil Science, University of Vermont email@example.com
have a high demand for nitrogen (N). Grass hay trials have shown
that some grasses will respond in yield up to 300 and even 400 lbs of actual
N per acre per year. The economic “break even” application
rate of N depends on the cost of N fertilizer and the value of the hay
crop. For hay, this is generally between 100 and 200 lbs N/acre split
two to four times per year, depending on the particular grass specie, soil
type and weather conditions. For pasture, the decision to apply N
becomes more complicated. Here are a few points to consider when
making N fertilizer decisions.
A Management Tool - Think of N fertilizer as
a short term management tool for producing temporary increases in pasture
dry matter. It usually shows an immediate response and then it is
gone. For your farm, you may decide that you don’t need N at all
or you only want to use it on certain acres for certain times of the year.
Stocking rate - Do you need the extra forage
that will be produced by adding N fertilizer? Some farms have more
land than their animals need. Adding N would just add to the pasture
waste. On the other hand, if your operation is stocked right
at that point where most summers are a stretch, then N fertility may be
an option to increase forage dry matter.
Legume content - Yields from legume forages such
as clover, alfalfa or trefoil are usually not limited by a lack of nitrogen
since they “fix” N from the air. If your pasture has over 30% legume
(which is a lot more than you might think), you are not as likely to see
a yield increase by adding additional N fertilizer. In fact, continual
additions of N will cause a shift from a legume-based to a grass-based
pasture, thus, increasing your reliance on N fertilizer to maintain production.
You may decide that a $30 per acre investment in lime which boosts your
legume growth is a better way of adding “N” to your pasture compared to
a $30 investment in N fertilizer which only has a short term effect.
The difficulty is that you can see the immediate affect of N, where as,
the response to lime is much more subtle.
Application Rate - For most applications, a rate
of 50 lbs N per acre per application works well. You will usually
“see” a good yield response at this rate in terms of growth and color and
yet it is not a high enough rate that you would need to be concerned with
nitrate accumulation. Your actual fertilizer rate will depend on
the fertilizer formula you are using. To get 50 lbs of N, divide
by the % N in your formula. For instance, urea is 46-0-0; therefore,
you would need to apply 109 lbs (50 divided by 0.46) to get 50 lbs N.
For ammonium nitrate (34-0-0), apply about 150 lbs. for a 50 lbs. N rate.
When to Apply N and When to Graze
- If you are rotating pasture, you get your best growth response by applying
right after the animals leave the pasture. For continuous pasture,
you may want to split your applications at lower rates, perhaps 30 lbs
N, just to reduce any risk of nitrate accumulation.
Early Spring Application - Applying N in early
spring can boost early spring growth for earlier grazing. However,
you would not want to treat too many of your acres or you will have a mountain
of pasture on your hands come late May! If possible, use your
best drained land to do this. Extremely wet soils causes N in the
soil to convert to a gas (called “denitrification”) which is lost to the
Summer Boosts - Applying N in early to
mid June can usually give a growth boost in summer pasture growth unless
it is an extremely dry year. On average, you might expect a 20 lb
increase in dry matter for every pound of N applied; therefore, a 50 lb
rate would boost yields by 1000 lbs per acre. With good grazing management,
this could potentially provide 30 to 35 additional grazing days per animal
unit (1000 lb animal). Remember, N is not the answer to grass growth
during dry years.
Fall Stockpiling - Allowing certain pastures
to accumulate growth in late summer and fall is a good way to “extend”
the grazing season into late fall. If your pasture is predominately
orchardgrass or tall fescue, applying 60 lbs of N per acre by early to
mid August, can really boost your stockpiled forage. If your pasture
is mainly bluegrass, apply 40 to 50 lbs N. Remember, this needs
to be done by mid-August to really see the yield increases for late fall
This site is maintained by Sid.Bosworth@uvm.edu,
Plant & Soil Science Department, University of Vermont.
Issued in furtherance of Cooperative
Extension work, Acts of May 8 and June 30, 1914, in cooperation with the
United States Department of Agriculture. University of Vermont Extension,
Burlington, Vermont.University of Vermont Extension and U.S. Department
of Agriculture, cooperating, offer education and employment to everyone
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