Top Crop Manager

Features Agronomy Fertility and Nutrients
Crop nutrition decisions key to 2005 yields

Check with experts for advice for the coming season.

November 15, 2007  By Top Crop Manager

32aSoil fertility and crop nutrition are key to producing maximum crop yields.
But for growers to get the best return on their fertilizer investment, annual
soil tests are essential to determine soil fertility and crop nutrient requirements.

Crop nutrition experts Gord Androsoff, a Saskatoon based CCA and agronomic
crop enhancement specialist with Agricore United, and John Heard, CCA and soil
fertility specialist with Manitoba Agriculture, agree that soil tests will be
especially important for the 2005 growing season because 2004's poor weather
will make it difficult to predict what happened to soil nutrients.

2004 weather effect on soil fertility
Although conditions will be different across the prairies, Androsoff and Heard
advise that growers need to consider the implications three weather-driven factors
will have on this year's crop nutrient requirements: good 2004 vegetative growth,
nitrogen mineralization or losses from high growing season precipitation and
crop residue returned to the soil.

For regions that are typically dry, Androsoff notes that good moisture in 2004
meant excellent vegetative growth, which reduced N levels in the soil. "We
had a lot of moisture and you would anticipate a large draw of nutrients from
the soil to support vegetative growth," says Androsoff. "However,
in some areas, you may find that N is also being returned to the soil at an
elevated rate."

Androsoff says growers in these typically dry regions should soil test because
there may actually be more N in the soil this spring than they thought. "With
constant good moisture in 2004, soil microbes may have been more active at converting
organic N to inorganic plant available N. I saw a couple of fall soil tests
where the N levels were higher than anticipated and I'm speculating microbial
activity had a role in that," explains Androsoff.

He also notes that prairie growers who were hit with frost last year may need
to tweak their 2005 nutrient applications to compensate for the impact of last
year's growing conditions and harvest decisions.

In the fall of 2004, severe crop damage from frost or other factors prompted
many growers to leave entire crops, residue and seed, in the field. Frost also
negatively impacted seed yield and quality of harvested crops by limiting the
amount of nutrients reaching the seed. This is important to note because growing
conditions were good prior to the frost and crops still had a significant nutrient
draw from the soil to support vegetative growth. Most of these nutrients, however,
never reached the seed and were left in crop residue that is now lying in fields.

In both situations, Androsoff says plant material left in the fields will eventually
add to plant available N in the soil. However, this N will slowly become available
later in the 2005 growing season and should not be counted on as a N source
for 2005 planting.

Heard says that Manitoba growers, who typically receive adequate moisture but
were soaked in 2004, can expect to see lower N levels in their soil nutrient
profile this spring. "Mother Nature worked the soilbank with mostly withdrawals
last year in the form of high yields and grain removal. Some grain samples showed
protein was low in wheat, suggesting the crop extracted most of the available
N," says Heard. "What few fall soil tests I've seen tended to show
very low N carryover."

In contrast to Androsoff's observation of typically dry areas, Heard says microbes
probably mineralized less N from soil organic matter in Manitoba last year because
soil conditions were too cool for optimal microbial activity. "Because
of saturated spring soils in 2004 we suspected leaching on sandy soils and denitrification
on the clays, which reduced soil N levels," says Heard.

He notes further that like other prairie regions, many long season crops in
Manitoba did not mature and, as a result, were not harvested. Not harvesting
the crop means nutrients will be tied up or locked in the residue and will not
be available until the late portion of next growing season. Heard says that
"Unlike green manure crops which can release 50 percent of their N the
next year, last year's immature crop residue will have a delayed N release during
the 2005 season."

Heard recommends growers who did not harvest immature crops work closely with
an agronomist to determine nutrient requirements and be careful when accounting
for N additions from crop residues. "I encourage growers to be conservative
when it comes to crediting N release," explains Heard. "This organic
N will release later in the season and be a benefit to long season crops but
less valuable to canola and cereals. It could benefit spring wheat by building
protein but be a detriment for malting barley."

Take advantage of 2005 yield potential with nitrogen
When planning for the 2005 crop season, Androsoff reminds growers that they
already have the most important yield determinant: moisture. In general, a crop's
potential yield is determined by available soil moisture, which growers in typically
dry regions may have more of this spring. Growers can help control how much
of the crop's yield potential is actually produced by using soil tests to determine
nutrient requirements and fertilizing to meet these requirements.

With high levels of available soil moisture leading to high yield potentials
for 2005, growers have a greater opportunity to get an excellent return from
a fertilizer investment, notes Androsoff.

According to Heard, it all comes down to what is a yield builder and what is
a yield protector. "You don't build yield with herbicides, fungicides or
insecticides, you only protect the yield that has already been set," says
Heard. "Moisture will set the upper yield potential and meeting that nutritionally
with fertilizer will determine how close to that potential your yield will get."

Both experts agree that because of 2004's unusual weather conditions, it is
very important for growers to consult with their crop advisors regarding soil
fertility and crop nutrition for 2005. Crop advisors will be able to help interpret
soil test results, determine yield potentials and recommend the most economic
N application rate to make efficient use of soil moisture and generate maximum
yields. –

Achieving fertility requirements during
the spring crunch
2004 growing conditions and delayed harvest will have many
growers concerned about how to meet spring crop nutrition requirements
without delaying seeding. Androsoff and Heard provide the following suggestions
to help growers save time.

Spring soil sampling
Without fall soil tests, it is important to complete spring soil sampling
before fertilizer applications. Contact your crop advisor or local provider
this winter to book soil tests in advance. Androsoff suggests working
with your crop advisor to select and test indicator fields with similar
rotations and management. This will provide growers a basis to make nutrient
decisions if time prohibits testing of all fields.

Booking fertilizer
Providing growers have storage space, pre-buying fertilizer will ensure
it is available when needed. Growers should also have worked with an advisor
this winter to determine fertilizer needs and potential purchases. This
will eliminate surprises and cushion growers from supply shortages at
the retail location.

Fertilizer application methods
Time may prohibit applying NH3 or banding N and
growers may need to consider alternative methods such as seed-placing
or broadcasting. Again, consult a crop advisor to determine the most appropriate
and safe application methods to use as well as pre-book any required equipment.

Timely seeding is top priority
Focus on getting your crop off to a quick start. Fertilizer or herbicide
applications should not take priority over timely seeding or generating
plant stand.



Stories continue below