NORCROSS, Ga. The
Symptoms of soil compaction often
go unnoticed until harvest. Without
close inspection of the root system,
or soil probing to evaluate resis
tance to penetration, it is difficult to
determine if compaction has been a
silent yield robber. There are some
secondary symptoms that can help
provide clues to this hidden prob
lem. Early wilting in field is a tell
tale sign when other fields, or areas
in the same field, fail to show indi
cations of drought stress. Slow
water infiltration and percolation
after rainfall, in areas where surface
drainage is not a limiting factor, can
also be a clue that compaction
exists.
Compaction is often caused by
heavy equipment and tillage,when
the soil is trafficked at improper soil
moisture levels. In some soils, com
paction occurs where the sandier
Don’t Overlook Compaction As A Yield Robber
surface soil meets the subsurface
soil layer having a higher silt and
clay content. It can range from
slight to severe and usually is
encountered at the bottom of the
normal tillage depth. If a disc is the
tillage tool, compaction often begins
4 to 6 inches deep and may extend to
8 or 9 inches. In plowed and chisel
plowed fields, the compaction usual
ly begins at 8 or 9 inches deep and
can extend to the 12 to 15-inch
depth.
Root penetration and aeration are
decreased in compacted soils.
Compaction reduces root access to
potassium, nitrogen, phosphorus,
and other nutrients. It slows soil
warming in the spring, can increase
denitrification losses of nitrogen,
and indirectly contributes to
increased erosion potential by caus
ing greater runoff. Increases in fer
tilizer rates can partially compen-
Foraging Around, Lancaster Farming, Saturday, February 13, 1999—Page
sate for reduced nutrient utilization
efficiency, but are really only a tem
porary solution where opportunities
exist to disrupt compacted soil lay
ers with appropriate tillage.
Banding or row-applying fertilizer
can also help offset reductions in
root access to nutrients in compact
ed soils.
Subsoiling to disrupt compacted
soil layers can increase corn yields
as much as 20 to 30 busnels per
acre for some soils. Wheat response
can parallel corn response. While
soybeans are often considered less
responsive, yield increases can
exceed 10 bushels per acre. Recent
work in the Mississippi Delta on cer
tain silty clay and clay soils showed
soybean yields increasing from 18
bushels per acre without subsoiling
to 41 bushels per acre with fall sub
soiling, followed by a dry growing
season, since the effectiveness of
subsoiling varies, local research
results should be reviewed before
this practice is implemented.
A diversity of subsoiling equip
ment is available and being used
where compaction has been recog
nized. Offset shanks, sometimes
preceded by rolling coulters, can be
used where reduced tillage and no
till systems are in place, to avoid
heaving large clods on the surface
and to minimize disturbances of
crop residues. Subsoiling in a dry
fall and avoiding further tillage
before planting, especially with a
disc, shatters compacted soil layers
and may provide the greatest poten
tial responses. If reduced-tillage or
no-tillage is practiced for many
years, earthworm activity and
increased organic matter levels can
improve soil aeration and help min
imize compaction effects. However,
compaction can still occur and may
need to be disrupted. Use of con
trolled traffic patterns minimizes
the damaging effects, whether in a
no-till or tilled system.
Soils should be probed to see if
compaction is present, roots and
rooting depths should be examined
and subsoiling or deep chiseling
should be considered. Growers
should contact their crop advisers,
Extension specialists, or Natural
Resources Conservation Service
offices for more information on the
elimination of soil compaction. Plan
now for improved crop performance
in 1999.
For more information, contact Dr.
Cliff S. Snyder, Midsouth Director,
PPI, P.O. Drawer 2440, Conway, AR
72033-2440, (501) 336-8110. E-mail.
csnyder@ppi-far. org.
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