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Nitrogen
is the fertilizer nutrient needed by plants in the greatest amounts and it
is the one that results in the most dramatic increases in forage growth.
Anyone who purchases commercial nitrogen fertilizer on a regular basis and
who has purchased (or priced) this product recently is painfully aware
fertilizer prices have risen sharply in recent months. In view of the fact
prices had already risen a great deal in the past few years, the expense
of purchasing nitrogen fertilizer can now be described as downright
alarming.
Many
cattlemen, producers of other livestock and crop farmers are looking for
ways they might lower their fertilizer expenses, especially their nitrogen
(N) fertilizer bill. Strategies being considered include using legumes to
a greater extent to get the benefit of biological N fixation, using animal
manures or other organic waste materials as a source of plant nutrients,
or using less expensive commercial fertilizer products which they either
have not used before or have used very little. Although urea fertilizer is
nothing new, there are probably at present more questions being asked
about it than have ever been asked before.
As
a dry fertilizer material, urea has an analysis of 46-0-0. In other words,
one hundred pounds of dry urea contains 46 pounds of actual N and no
phosphorus or potassium. By comparison, 100 pounds of granular ammonium
nitrate contains 33.5 pounds of N, and 100 pounds of ammonium sulfate
contains 21 pounds of N (plus 24 pounds of sulfur). Fluid or liquid urea
has an analysis of 28-0-0 or 32-0-0. Traditionally, urea-N is about 2/3
the cost of ammonium nitrate-N.
The
cost of N from various fertilizer products varies over time, so it makes
sense to calculate the cost per pound of N various sources will provide.
In the case of ammonium sulfate, the sulfur this product contains has
value because sulfur is also essential for plant growth. However, sulfur
has the "downside" of lowering soil pH more quickly than urea or
ammonium nitrate, thus resulting in the need to make a lime application
sooner than would otherwise be the case.
There
also is something else to consider with urea…under certain conditions
there can be significantly more volatilization loss (gaseous loss of N
into the atmosphere) with this product, regardless of the urea formulation
being used. The amount of volatilization loss can vary from none to over
50 percent. With the potential loss being this high, it makes sense for
producers to understand what situations lend themselves to significant
levels of volatilization.
Several
factors affect the likelihood of substantial volatilization loss. If the
soil pH is alkaline (above 7.0) the risk is greater than if the soil is
acidic (pH less than 7.0). Fortunately, except for certain Black Belt
soils, this is unlikely to be a problem in Alabama. If the soil is moist
or there is heavy dew, the volatilization risk is increased; on the other
hand, if there is a rain within 24 hours after application, there will
likely be little volatilization loss. Soils with a low cation exchange
capacity are more vulnerable to volatilization loss than soils with a
higher cation exchange capacity. Also, the more vegetation present on the
soil surface, the higher the potential volatilization loss.
The
last and perhaps the most widely applicable factor to consider is
temperature. When soil temperature is less than 50 degrees Fahrenheit,
there is low likelihood of volatilization. Therefore, urea can normally be
applied between around |
