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Northcentral
Many in agriculture are concerned
about higher fertilizer prices. Here are a few
key concepts to remember when thinking about a
phosphorus (P) and potassium (K) fertilization
program.
- Soil testing is the best tool for
indicating whether or not a soil should receive
fresh supplies of nutrients. It is a worthwhile
investment. Remember that if a soil sample represents
a large area, there may be areas within the field
with much lower soil test levels than the overall
result might indicate.
- Soils with higher soil tests do
not need additional broadcast applications of nutrients
in the short term. But remember to monitor crop
removal rates and keep testing the soil over time
to ensure that soil test levels do not drop lower
than desired. Soils with higher initial tests tend
to drop more rapidly than soils with lower tests.
- In some states, addition of nutrients
in a band applied near the seed at planting (termed
starter fertilization) provides early and late
season benefits, even on higher testing soils.
- Management of P and K depends on
land use. Short-term rental ground may be most
profitable to the renter if kept at lower, more
responsive levels. However, overall yield levels
may suffer. Land that is owned and cared for with
a long-term strategy is best built to higher levels,
where the risk of nutrient shortages is minimal
and the probability of higher yields is greater.
In lean years, these fields can be built more slowly
or maintenance applications made until economic
conditions improve.
- Use manure sources wisely. Whenever
possible, apply manure to fields that need supplemental
P and K supplies. Get the manure tested and keep
good records of where in the field applications
were made. This will allow you to determine how
much of each nutrient was applied and where it
all went. If you occasionally scrape pits, remember
that there is a good supply of P in the manure
solids that collect at the bottom.
It is important to recognize that
there is no one strategy that fits all scenarios,
even on one farm. Accounting for all sources of nutrients
will ensure that purchased nutrients are used only
where needed.
Northeast
Soon forage plants will
enter the critical fall growth period, during which
they store the carbohydrates they need to survive the
winter. Adequate potassium (K) is essential for this
carbohydrate storage. August is an excellent time to
apply K fertilizers. Potassium is particularly likely
to run short if previous harvests have been heavy.
The amount to apply is an important decision. Make
sure it's based on a recent soil test, and supported
by forage analysis as well. Calculating a nutrient
budget – nutrients removed
by previous harvests minus the amounts supplied in
manures and fertilizers – can also help determine
the right amount to replace. For harvested cereals
underseeded to forage, K should have been supplied
at planting, but if it wasn't, applying as soon as
possible after cereal harvest will ensure the seedlings
develop into winter-hardy plants.
Winter wheat has performed well in
many parts of the region. For next year, assure yourself
a good start by planning for the fertility needs
of the crop to be seeded this fall. Nitrogen (N)
and phosphorus (P) are important components of a
starter to ensure a healthy stand. Wheat can be profitable,
as well as an excellent soil builder in the rotation.
Manure applications following harvests
of cereals and silage corn should be guided by soil
tests and manure nutrient analysis. Rates should
be appropriate to supply the soil's needs for P,
K and organic matter. Avoid wasting N by ensuring
a cover crop grows to absorb what is released from
the manure.
Northern Great Plains
Reading Soil Test Phosphorus
Results
In the absence of plant growth and soil erosion,
soil test phosphorus (P) changes very little . But,
as with nitrogen (N), soil test P declines due to crop
removal. As a result, many growers use P removal estimates
to determine their crop requirements as well as maintaining
their soil P levels.
Soil buffer power is the factor which
makes a big difference between mobile nutrients like
N and immobile nutrients like P. The capacity of
the soil to re-supply P to the soil solution after
crop removal defines its buffer power. A soil with
a high buffer power is fast to maintain P in solution
around the plant roots. Alternatively, a soil with
a low buffer capacity is not as capable of re-placing
soil solution P after crop uptake.
Routine soil tests do not measure
the buffer power of the soil, but they do measure
the nutrients in solution and a fraction of the nutrients
that may come into solution. Soils have different
properties that affect their P buffering ability
and the rate of P replenishment. Amount and type
of clay minerals, organic matter level, other soil
constituents, and fertilizer P history are all important
contributors.
Buffer
power increases with increasing clay and organic
matter content, as does the ability to influence
soil test P with fertilizer additions . Soils with
high buffer power (high organic matter and clay)
need more P fertilizer to increase their soil test
level than soils with low buffer power (high sand
and low organic matter). Typically, 14 to 22 pounds
of P2O5 per acre is required to increase a P soil
test by 1 part per million (2 pounds per acre).
Southern/Central Great Plains
The region continues to be in relatively
good condition in terms of drought. The latest index
(Palmer, 8/6/05) shows medium to severe drought in
eastern Texas and Oklahoma, and in eastern and southern
Colorado. The remainder of the region ranges from normal
to extremely moist. Row-crop condition is generally
not as good as last year, but is still above normal.
The percent of corn rated between fair and excellent
as of August 8 is 85 for KS, 88 for NE, 91 for OK,
and 71 for TX. The percent of the soybean crop rated
between fair and excellent is 88 for KS, 83 for NE,
94 for OK, and 66 for TX. Percent cotton rated between
fair and excellent is 85 for TX, 81 for OK, and 84
for NM.
Preparation
for wheat planting is well underway. Growers and
their advisors should remember that phosphorus
(P) nutrition of wheat is a critical factor in
achieving optimal yield. Although only small amounts
of P are taken up by wheat early in the season,
it nevertheless plays a major role in early plant
development and determination of attainable yield
potential. During the first few weeks, P supply
increases the proliferation of roots as well as the
initiation of tillers. An insufficient supply early
in the season creates irrecoverable yield losses.
Phosphorus shortages later in the season have less
impact than those encountered earlier. Although higher
soil fertility levels are important for season-long
P nutrition, early season P supplies must be accessible
to the limited root system of the young wheat plant.
For this reason, P placed near the seed at planting
(starter P) has proven effective, especially in cold
soils. The response of wheat to low rates of starter
P is often referred to as the “pop-up effect”,
and is marked by improved leaf and root growth, tiller
formation, and yield. Some research has indicated
that starter P can provide benefits even at higher
soil test levels, probably because of its superior
positional availability. Bottom line… make
sure wheat planted this fall has sufficient available
P so that yield potential is not compromised. Also,
remember that a well-managed fertility program must
consider the complete nutritional needs of wheat.
Southeast
Much of the Southeast region witnessed
a challenging planting season. Cooler, moist conditions
in much of the region were followed by an abrupt drier
period. Rainfall has appeared normal to slightly above
normal for the eastern portions of the region. Drought
has plagued much of Arkansas and Missouri, and much
of Louisiana has been abnormally dry.
Asian soybean rust has been detected
primarily in sentinel plots, and fortunately, only
in a few production fields to date. Several of the
sentinel plots have been destroyed to limit the potential
for spread of the rust spores. The map pasted here
depicts the counties in the Southeast region where
soybean rust presence has been confirmed, as of August
10, 2005. The hurricane season, so far, has not dispersed
the disease as widely as was feared possible. Vigilant
scouting by Certified Crop Advisers, independent
consultants, industry representatives, county Extension
agents, and farmers continues. Disease detection
and control treatments in the Southeast region may
help limit the potential for spread to fields in
the upper Midwest.
Extension
workers in several states have reported increased
symptoms of potassium (K) deficiency this summer.
Agronomists in Kentucky have pointed out that soil
test K levels may not be as high as some farmers
thought, after the exceptional yields produced the
last 2 years. Removal of K with past crop harvests,
soil compaction, a developing good yield potential,
and recent dry weather are factors that may have
contributed to the symptoms. All farmers should be
encouraged to have soil samples collected at least
every 2 years, to track trends in fertility over
time. Frequent sampling can identify problems that
can be corrected before the next crop.
Continued
storms and showers in Florida and Georgia hampered
some pesticide applications on peanuts and cotton,
and made hay harvest challenging. Vegetable production
and peanut yield potential is being affected by increased
diseases. Watermelons are ripening and pecans look
good. Rice harvest has begun in southern Louisiana
and initial yield reports are favorable. Corn is
drying down and harvest has begun in some states,
but much of the corn is just approaching the dent
stage. Wet and cloudy weather in the more eastern
states has caused some shedding of cotton squares
and bolls, while drought is resulting in fruit abortion
in parts of Mississippi, Tennessee, and Arkansas.
In Mississippi, early maturity soybeans were beginning
to shed leaves as they mature. Some April-planted
Maturity group IV soybeans were harvested in Arkansas.
According to the Florida Ag Statistics
Service, citrus growers in some of the southern Florida
counties are pumping excessive water out of their
groves. Fertilizing, spraying, and care of hurricane-damaged
groves and young trees have occupied grove managers.
Pastures in Arkansas, Missouri, parts
of Tennessee and Kentucky have suffered from prolonged
heat and lack of moisture. Some ranchers have reportedly
begun to liquidate their stock because they can not
afford to purchase more hay. The heat is also taking
a toll on livestock weight gains.
There are
rumblings among farmers… and
some fertilizer sales people are worried that farmers
may balk this fall in purchasing needed plant food… because
of the higher fertilizer costs. The recently signed
U.S. trade agreements, foreign competition, international
trade pressures to abandon commodity support programs,
and the U.S. administration’s intent to phase
out subsidies has many farmers in the southeast concerned
about their future. There is speculation that some
farms will be sold and that the better managers will
purchase or rent the available land, such that the
total acreage farmed may not change greatly. It seems
likely that fewer farmers will be making larger purchases
and sweeping management decisions. Many farmers who
are good managers know the value of maintaining soil
fertility to protect yield potential, since they
have no influence over crop prices.
West
As the growing season
slows down and before the winter rains begin, it is
a great time to take soil samples and start planning
for the next season. Soil testing is the best way to
determine the soil’s ability to supply nutrients
for crops. As a best management practice (BMP), soil
testing not only provides a key component for environmental
monitoring, but it is also the best predictor of economic
and agronomic returns. As fertilizer prices respond
to increasing global demand, making crop health decisions
without the right information is very short-sighted.
Farmers and crop advisers need to make management decisions
based on good information – and not just a quick,
poorly thought-out reaction to the fluctuating price
of crop inputs.
Given the essential role of soil testing
in making correct management decisions, collecting
proper samples is critical. This means taking samples
from representative areas in the field, identifying
special management zones (such as those receiving
manure), and accounting for differences in the landscape.
Taking good soil samples will take the guess work
out of management decisions and help get the most
return from your fertilizer investment.
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