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ISSUE 4   MAY 27, 1999

 

YELLOW CROPS

    There have been reports of yellow crops on emergence, especially small grains. It is important to remember
before jumping to conclusions that some of these crops have been seeded for several weeks and are just
emerging or are still very small. With the degree of stress these young plants have been under, it is
understandable that some yellowing is likely. However, there have been reports of fields that had N applied
in early fall (before Oct. 1) that appear more yellow than crops emerging with later N applied (late fall or
applied this spring). This suggests that the yellowing is a nitrogen problem of some kind.

    If the soil texture is loam or coarser, some leaching would be expected in areas receiving more than two
inches of rain this spring. In some of these cases, most of the N may still be in the root zone, but may be too
deep for the crop right now. A soil sample taken at the 0-6 inch and 6-24 inch depth would explain if the N is
shallow or deep. If the soil texture is silt loam or heavier, particularly the clays in certain parts of the state
including the Valley, there may have been significant low levels of denitrification that allowed the N to be
transformed into nitrous gases this spring as the temperature warmed and the soils became saturated. Again,
a soil sample would give a good indication whether the N was there or not.

    By now, most ammonium N has been transformed to nitrate. If ammonia was applied, take the soil cores
closely spaced perpendicular to the application direction at least across one width of anhydrous applicator
spacing. If there needs to be supplemental N applied, top-dressing small grains is the only viable option.
Avoid liquids which tend to burn leaves. Remember that urea-N needs to have a rain within 48 hours to
avoid significant volatility and loss.

 

SOYBEANS SEED-PLACEMENT REVISITED

    This is wheat country and producers are likely to want to apply fertilizer with seed as a matter of course. One
would be hard-pressed to convince long-time soybean growers from Iowa that this is a good idea in soybeans
because this lesson was learned long ago. However, it is just beginning to be learned in the new expanding
northwest territories of soybean production.

    Soybeans cannot tolerate fertilizer with the seed, especially when it is concentrated in row widths of greater
than 15 inch spacings. Stands have been reduced by 2/3's with what we would consider modest rates of
fertilizer for small grains at those row spacings. We allow (not particularly comfortable, but allow) as much
as 10 lb N/acre with the seed in double-disc drill spacings of 6-7 inches, but the level is reduced as the
fertilizer concentrates in wider row spacings. There are numerous studies, however, to suggest that soybeans
prefer fertilizer broadcast rather than band. Since soybeans require little supplemental P fertilizer at medium or
higher soil test levels, the recommendation is to forego fertilizing beans unless the soil test P level is very low
or low and instead add the recommended fertilizer to crops before or following soybeans that tend to respond
more. Soybeans are a good scavenger of P, unless soil test levels are very low or low.

    If P needs to be applied, it would not be unlikely to expect 2-3 bushels more soybeans if the fertilizer was
broadcast rather than banded. Some of this increase may be because soybean roots are sensitive to salt and
may shy away from banded fertilizer instead of utilizing it. Another reason suggested is that the soybean roots
need to be bathed in nutrients, and are inefficient in picking up the concentrated bands. Therefore broadcast
is better than banded.

    Take note of the soil test P level to determine if you really need the P this year at all. If high levels are
needed, consider broadcast-it could mean a couple bushels more at harvest. Do not put fertilizer with the seed
in 15 inch rows or wider. Although it is referred to as "pop-up" fertilizer generally, in the case of soybeans
it might more appropriately be labeled "pop-down"!

Dr. Dave Franzen
NDSU Extension Soil Specialist

 

 


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