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Field Nutrient Variability – How to
Improve Low-production Areas
Nothing reveals field variability as vividly as a yield map. Producers are often
surprised to see how close high-yielding areas are to very low-yielding areas.
"A yield map shows you where a field's aches and pains are," says Dr. Charles Wortmann,
nutrient management specialist with the University of Nebraska at Lincoln. "Once you locate areas of low
productivity, you will have to work with those parts of the field to identify the exact problem. Sometimes a low-yield problem can be fixed, but other times you simply have to live with the cause."
Look first for soil compaction. Perhaps an event happened that caused compaction in one
part of the field, or perhaps that area is simply more prone to compaction. Wortmann says that this problem can often be corrected by deep tillage when properly done.
Fertility Analysis
"Soil texture, organic matter and nutrients like sulphur, potassium copper and boron
are randomly distributed," says Elston Solberg, a soil nutrition specialist affiliated with Agritrend
Agrology in Red Deer, Alberta. "The most intense problems are found wherever interfaces occur. Copper
deficiency, for example, will be most prevalent where the copper deficiency overlaps the high organic
matter."
According to Solberg, the most significant fertility variations in fields often occur
with sulphur. Variations can range from insignificant amounts up to several thousand pounds within a
field. Soil copper can be 20 times higher in one part of the field than another.
"If you happen to take a soil sample from a nutrient-rich part of the field, it can
indicate that you have excessive nutrients when, in reality, 79 percent of the field is deficient,"
says Solberg.
Soil pH
Organic matter and soil pH also fluctuate within fields. Solberg says years of soil
studies at many sites show that pH can vary by two units. An averaged soil sample that shows the field
has a pH of 6.7 can actually mean that the pH in the field ranges from 5.7 to 7.9.
"Depending on where in North America you are, organic matter can vary by 3 to 4
percent and perhaps even more," Solberg says.
"In some areas of the Great Plains, parts of a field may need lime applied for
acidity," Wortmann points out, "but productivity in other parts of the field may be reduced because
pH is already above an optimal level. Since a lime application is expensive and with a lot of field
variation in lime requirements, specific management technology can be a profitable option."
Solberg says: "Field variability exists, but it's not a problem if we understand
it. Soil sample numbers are not absolute. They're ballpark numbers that give you a platform to work
from and help you connect diagnostic dots."
GPS Random Soil Test
Solberg suggests combining GPS tags with random soil and tissue testing to
eliminate many of the variations in soil testing and to verify that your nutrition plan is working.
"The first year collect soil samples for a standard random soil test," Solberg
explains. "GPS reference all sample holes accurately. The second year and several years after that,
return to the exact same spots to test. Anchoring the sites allows you to see what your levels were
in 2003 and compare them to levels in 2004 and to future years. This eliminates the possibility
that you are randomly punching soil samples from different parts of the field. You will start to
know for sure if your phosphorous or copper levels are creeping up and can also evaluate the impact
of your nutrient management plans."
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Seedling Health – Give them the full
meal deal
If you want even productivity across the field, your first job is to set the stage
for fast root development and the second is to foster uniform emergence.
"Plants are not that different from animals
or people," says Ivan Reike, marketing and training manager
for soil preparation with CNH in Goodfield, Illinois. "Keeping
young plants healthy helps them cope with any stresses they receive
later on."
Since most crops prefer to grow in a neutral pH soil, balancing the pH across a
field may mean treating acidic soils with limestone; alkaline soils are a little tougher to work with.
"Alkaline soils tie up nutrients a bit differently than acidic soils," Reike says.
"This is why a well balanced fertilizer package is important. If you can't get your pH in balance,
then banding fertilizer under the row will allow the crop to make better use of the nutrients.
Fertilizer placed in a band isn't as tied up by the soil structure.
"Banding also lets you make better use of
your fertilizer dollars, and it can reduce the chance of nutrients
escaping into the watershed systems. It is also more environmentally
friendly and agronomically sound. These are some of the reasons
banding is popular."
"The producer can regulate the fertilizer depth by shooting into the sidewall
instead of dropping it into the bottom of the tillage location," says Reike. "Combined with a GPS
system, it's also a great way to treat soil compaction and enhance the crop agronomically."
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