Features Agronomy Fertility and Nutrients
Forage fertility… planning for 2007

Using fertilizer to restore the productivity of an established forage crop
pays major dividends, with the proper balance of all the essential nutrients
critical to maximizing yields. Soil testing is key to ensuring that multi-nutrient
deficiencies are addressed in fertilizer management programs.

Forage crop fertilization is considered an optional practice by some farmers,
but an essential practice for those striving to maximize livestock and land
productivity. In some regions, dryland forage yield may be limited by a lack
of rainfall. However, where irrigation is available, high forage yields from
multiple cutting harvest programs provide an abundance of high quality hay.

Liquid dribble band is preferred over broadcast N. Photo Courtesy Of PPI/PPIC.

There is a large database to support fertilization of forages as a means of
maintaining yield, quality and stand longevity. In fact, the true cost of not
fertilizing becomes much higher when the impact of declining stand productivity
is included. As long as the quality of the forage plant stand has been maintained,
the ability to rejuvenate forage production with fertilizer additions has great
potential.

Forages are large consumers of nutrients, especially given the whole crop removal
of the nutrients taken up. Unlike annual grain crops, where most of the crop
residue is left in the field, almost all of the above-ground biomass of forages
is removed at harvest. As a result, some nutrients such as phosphorus (P) and
potassium (K) are more likely to become deficient faster than with grain crops.
The amounts of nutrients removed in forage is shown in Table 1.

Forage fertilization to overcome nutrient deficiencies can pay big returns
on the investment. However, timing this fertilizer application varies considerably
based on where in North America you are farming. For forage production, early
spring fertilizer application is considered the best time in many areas. This
early timing provides the forage crop with an adequate supply of nutrients during
the initial spring growth period.

How should fertilizer be applied to forage crops?
If you have the resources to apply sufficient rates of P and K for multiple
harvests before the crop is seeded, then banding is a good option to consider.
The mobility of nitrogen (N) in the soil generally limits its use to annual
application on forage crops. Once established, broadcast application is an effective
means of applying the nutrients. A healthy forage crop has an abundance of surface
roots which can take up surface-broadcast nutrients, which is not the case in
newly established stands. Research trials show that a slight improvement in
P uptake may occur when it is band-applied into established forage stands, but
the added cost of application was often hard to recover with this slight yield
improvement.

Dribble banding of fluid fertilizers onto the soil surface is also another
effective means of supplying nutrients for forage crops. Dribbling is generally
preferred over broadcast application since more of the nutrients come into contact
with the soil where they can be taken up by the roots. Broadcast applications
are generally less efficient since a significant portion of the nutrients may
stay unabsorbed on the foliage and because N applications are more susceptible
to gaseous loss when applied with this method.

Research trials conducted in the northern Great Plains showed that either broadcast
or surface dribble bands of fertilizer were similar in their effectiveness,
while little advantage was captured from coulter injection of a fluid fertilizer
(see Table 2).

How does balanced nutrition optimize forage response
to fertilizer?
Forage productivity often declines as a result of more than one nutrient being
deficient. For example, applying N to a forage when there is also a P deficiency
will not provide much of a crop response. In the trial, one of the locations
had a severe P deficiency. When N was applied alone, there was little response.
However, when N was applied with P, forage yields increased by 300 percent over
the period of the study. Testing the soil and the forage will show if a multi-nutrient
deficiency may be limiting the response to any single nutrient.

Forages remove large amounts of nutrients from the soil. Photo Courtesy Of Bruce Barker.

Phosphorus deficient forage stands generally show a progressive response to
fertilizer P over several years. Where a P deficiency is limiting forage yield,
it is common to see a good response to P application in the first year, with
further increases following continued application in Years 2 and 3. This cumulative
response reflects the nature of fertilizer P availability to crops, as it continues
to become plant available in Year 2 and 3 from the previous year's application.
In the study shown in Table 2, applying 90lb/ac of P2O5
in Year 1 and no P in the next two years provided superior yield responses to
applying 30lb/ac P2O5 per year
through the three years of the project. While the costs of a high rate of P
application may limit its use, these results confirm the strong response of
the crop to N application when the P needs have been met. Remember that it is
best to anticipate forage nutrient needs prior to establishment rather than
try to correct deficiencies and compensate for lost yields.

Where the productivity of established forages has declined over time due to
nutrient deficiencies, fertilizer additions can be an effective means of improving
yields. Soil testing to evaluate the level of available nutrients is critical
to ensure that all deficient nutrients are applied. Correcting P deficiency
is essential before achieving a profitable N response in forage crops.

Dr. Adrian Johnston is Northern Great Plains Director for PPI and
Dr. Rob Mikkelsen is West Region Director for PPI. Article reprinted with
permission from PPI/PPIC.