Soil Temperatures And Spring Prospects
URBANA, Ill.
With hopes that we’ve seen the last of the snow by now, but both air
and soil temperatures remain below average in Illinois heading into the
second half of March, said a University of Illinois crop sciences
researcher.
Emerson Nafziger said that soils froze deeper than normal this past
winter and stayed cold into March. Frost is only now disappearing in the
northern parts of Illinois, which accounts for their staying cold even
during a sunny day.
“Hopes that such deep freezing will relieve soil compaction from last
year may not be realized, while repeated freezing and thawing results
in repeated formation of ice crystals that force soil particles apart,”
he said. “Soils that stay frozen, don’t repeat this cycle often enough
to do much good. The freezing and thawing of the surface soils that
we’re seeing now will help loosen them some, but we can’t expect that
effect to extend more than a few inches deep.”
According to the Illinois State Water Survey
(http://www.isws.illinois.edu/warm/soiltemp.asp), minimum temperatures 4
inches deep under bare soil ranged from the low 30s in northern
Illinois to the mid-30s in southern Illinois the morning of March 17.
There was some sunshine on that date, and soils warmed to the upper 40s
to low 50s in southern Illinois, but stayed in the low 30s in the
northern part of the state.
Although having soil temperatures only in the 30s this late in March
is somewhat unusual, Nafziger said March soil temperatures have varied
over the years. At Champaign, March soil temperatures at 4 inches deep
have ranged from the 30s to the 60s just over the past five years, from
an average of 36/39 (minimum/maximum) in 2013 to 60/66 in 2011.
Rainfall totals ranged from 1.47 inches in 2013 to 5.38 inches in 2011.
Still, delays in planting have been more related to April rainfall than
on conditions in March.
When it comes to getting soils to dry out, is warm and wet better or worse than cold and dry?
“Because water has a higher heat capacity than soil mineral matter,
cold soils do not dry out very fast and wet soils do not warm up very
fast. We have seen some of the standing water in fields drain out this
past week as soils thaw, but the drying process will be very slow until
soil temperatures start to increase,” Nafziger explained. “Water loss
rates are affected by soil texture and water content, but we would
expect wet soil to lose a tenth of an inch or so of water in a day if
the average soil temperature is 40 degrees and at least twice that
amount if the average soil temperature is 60 degrees. So having soils
warm up is the key to enabling them to dry out, though it has to stop
raining for soils to dry, of course.”
While having low soil temperatures at this point in March may not
produce a lot of optimism that planting will start early, Nafziger said
it is also not a very good predictor of how the spring will go, or what
kind of season growers will have. “If we’ve learned anything in recent
years, it’s that what happens during the summer matters much more to the
crop than what happens in March and April. We simply need to be ready
to do fieldwork and plant as soon as conditions permit,” he said.
The likely delay in the start of field work this year may mean
re-prioritizing operations once soils dry out. It has been common in
wetter springs for the application of anhydrous ammonia to get under way
before soils are considered fit to till or plant. “That worked okay
last year when soil compaction due to weather patterns did not cause
much problem for the crop. But we can’t count on that, and compaction
from applying fertilizer or doing tillage in wet soils can leave soils
in worse condition than before, even if the surface looks a little drier
afterwards,” Nafziger explained.
As a reminder, planting in early April almost never produces yields
higher than planting in late April and can lower yields even when stands
are good, he cautioned. Planting in early April into good soil
conditions, with soil temperatures expected to be on the rise after
planting, is a sound practice, especially when there are a lot of acres
to plant and starting early is the only way to finish on time.
“But ‘mudding’ corn into wet or marginally wet but cool soil
conditions in early April is almost always a bad idea, with considerably
more potential to do harm than to do good,” Nafziger said. ∆