Phosphorus, Potassium Management Of Forage Crops
NORCROSS, Ga. High yield
ing, quality forage production is
critical to achieving a desired level
of animal performance and profita
bility.
Good forage growth places a
heavy demand on the soil’s nutrient
supplying power. Whether the
forage is for grazing, winter feed, or
sale, optimizing production requires
that soil nutrient deficiencies be cor
rected.
Phosphorus and potassium are
key elements in forage crop estab
lishment and year-to-year produc
tivity. Forage crops require
phosphorus for photosynthesis,
energy, cell division, carbohydrate
production, protein synthesis, root
development and early growth,
winter hardiness, and nitrogen fixa
tion. Potassium plays a similar role
in addition to improving the crop’s
tolerance to drought and minimiz
ing susceptibility to disease. When
in proper balance with nitrogen,
sulfur and micronutrients, sufficient
phosphorus and potassium ensure
high yields of quality forage.
The annual removal of phos-
For
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phorus and potassium by forage
crops is high relative to annual
cereal, oilseed, and pulse crops. Al
falfa removes approximately 15
pounds P 2 Oj per ton and 60 pounds
KjO per ton of forage production.
The values for grass hay are 11
pounds P 2 O s and 45 pounds K 2 O per
ton. With these rates of nutrient re
moval, it is easy to see how forage
stands can rapidly decline in pro
ductivity on soils with either low
phosphorus and/or potassium levels
or in the absence of nutrient appli
cation with fertilizer or manure.
Forage crop phosphorus and po
tassium requirements are best deter
mined using a combination of soil
testing and crop nutrient removal.
Soil sampling those areas that repre
sent the good producing areas of the
field is the best way of assessing soil
nutrient supply. If the field is highly
variable, it is better to take several
soil samples from each of these dis
tinct areas, as opposed to taking a
composite sample. Composite sam
ples in variable fields tend to mask
possible problems, and can result in
recommendations that either miss a
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possible deficiency or suggest ferti
lizer application where adequate
nutrients are available. Based on a
combination of average nutrient re
moval per ton of forage and annual
production levels, an estimate can
be made of the nutrient removal and
fertilizer requirements to correct po
tential deficiencies.
Given that phosphorus and po
tassium move very little in the soil,
their availability can be strongly in
fluenced by the method of applica
tion. Broadcast application and
incorporation of enough phos
phorus and potassium for several
years of forage production in the
year of forage establishment is an ef
fective means of ensuring adequate
nutrient supply. On soils testing low
in phosphorus or potassium, band
application methods tend to be su
perior to broadcasting.
Preplant banding concentrates
the nutrients in a limited soil
volume, reducing the opportunity
for reaction with the soil and lead
ing to reduced plant availability.
Once established, forage stands can
either be fertilized by surface broad-
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today 1-800-635-8708.
A
|i Lancaster
H LEVEL-FLO
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Mam Office Branches
Mount Joy PA Footville, Wt Zumbrola, MN
(717)653-2239 (608) 876-6146 (507)732-7886
Fax (717) 653-9806 Fax (608) 876 6147 Fax (507) 732 7925
www lancasterlevel-flo com
Foraglng Around, Lancaster Farming, Saturday, July 15, 2000—Page
cast application or injection into the
soil using a low-disturbance disk
coulter.
Research conducted in western
Canada has reported that subsur
face banding of nutrients can im
prove forage yield over surface
broadcast application by 800
pounds per acre per year for alfalfa
and 500 pounds per acre per year
when renovating mixed forage
stands. Low disturbance coulter in
jection allows for the maintenance
of forage yields in established
stands, while minimizing the
damage to the stand.
Optimizing forage crop yield and
quality demands attention to meet
ing crop nutrient requirements.
Forage producers can achieve this
with an understanding of crop nu
trient requirements for yield and
quality, as well as fertilizer applica
tion methods that maximize crop re
sponse.
For more information, contact
Dr. Adrian M. Johnston, Western
Canada Director, PPI, Suite 704,
CN Tower, Midtown Plaza, Saska
toon, Saskatchewan, Canada S7K
IJS, (306) 652-3535, e-mail; ajohns
ton@ppippic.org.
YA
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189