doi:10.2489/jswc.66.1.13A
Feature
No-till can increase earthworm populations
and rooting depths
W. Doral Kemper, Nicholas N. Schneider, and Thomas R. Sinclair
C
EFFECTS OF TILLAGE ON ABSORPTION
AND RETENTION OF WATER AND
CROP YIELDS
One aspect of the absorption and holding capacity of soils that appears amenable
to significant change by management is
the runoff-infiltration tradeoff. Edwards
and Norton (1986) found that with rainfall averaging about 100 cm y-1 (40 in
yr-1) at Coshocton, Ohio, a long-term,
well-drained, no-till watershed, planted
continuously in corn, had practically no
runoff, while runoff from a nearby watershed with tilled corn averaged about 12
cm y-1 (5 in yr-1). This additional water,
absorbed into the no-till profile, and generally stored until it was needed, played a
W. Doral Kemper is a soil physicist, retired
from the USDA Agricultural Research Service.
He is now consulting with the Pakistan Council
of Research in Water Resources and the Water
and Power Development Authority. Nicholas
N. Schneider is the agricultural agent for
Winnebago County, Wisconsin, and an associate
professor at University of Wisconsin Extension,
Oshkosh, Wisconsin. Thomas R. Sinclair is a
professor at the Department of Crop Science,
North Carolina State University, Raleigh,
North Carolina.
journal of soil and water conservation
positive role in the crop production in that
watershed during the 20 years of this study
and often helped fill the soil profile to near
field capacity. Corn residues from previous years were left on the surface of the
no-till watershed. However, tillage buried
most of the residues on the tilled watershed and accelerated their decomposition.
Eliminating tillage often helps maintain
the infiltration rate of water by leaving the
crop residue where it can protect more of
the surface soil from the aggregate disintegrating and surface sealing effects of falling
raindrops. Residues on the surface also
retard runoff during high intensity storms,
resulting in more water ponding on the
land surface, which is a prerequisite for it
to enter the soil via macro-pores formed
by soil fauna.
Absence of tillage also favors the development of large populations of Lumbricus
terrestris (L.t.) earthworms, also called
nightcrawlers.Their holes generally extend
from the surface to about the depth of
deepest rooting. These holes are usually
covered by small stacks of residue fragments from previous crops, called middens,
which have been pulled to that position
by the worms and cemented in place by
their excrement. These residue fragments
are generally infected by molds, whose
hyphae grow rapidly when the organic
residue is moist, and are grazed selectively
by the worms. These stacks of residue also
provide protection of the hole entries from
disintegrating raindrop bombardment and
sieve out some of the larger sediment particles when ponding water from intense
rainfall immerses entries and drains down
through these macropores.
Most of the seed planters available a few
decades ago had difficulty planting in soils
that were covered with substantial amounts
of crop residue because the residues would
bunch, or roll up, in front of the shafts that
supported the openers and tubes which
carried the seed into the ground. New
planters can cut through crop residue
on the soil surface, opening narrow slots
through which the shafts and tubes can
pass and in which seed and fertilizer can
be placed at the desired depths before the
slots are closed. However, when brighter
organic residue covers the darker soil above
the seed, the brighter area reflects more of
the sunlight.The organic residue also insulates the soil from the heat of the warming
spring air. These factors keep the daytime
temperature of the seedlings in the no-till
fields a degree or two lower than those in
the tilled fields. Plants in the tilled fields
emerge earlier and grow faster during the
beginning of the growing season than in
no-till fields. In years when no significant
growth-inhibiting water deficit is experienced by the crops during the rest of the
season, this head start for corn on the tilled
fields can persist through the growing
season and occasionally provides a yield
advantage for tilled corn in the northern
Corn Belt (Wolkowski 2007). However,
in years when significant drought stress
occurs during the growing season, no-till
corn often yields as well as or better than
tilled corn. Less wilting of no-till than of
tilled corn in the hot summer afternoons,
when there has been no rain for a few
weeks, indicates that absence of tillage has
enabled corn to draw more water from the
soil profile.
NO-TILL INDUCED INCREASES IN
ROOTING DEPTH AND AVAILABLE
PROFILE WATER
Merrill et al. (1996) reported depths of
rooting of wheat and sunflowers under
tilled compared to no-till management
near Mandan, North Dakota. As indicated
in the top half of table 1, they found deeper
rooting for both crops under no-till management. They attributed deeper rooting
under no-till management to better conservation of the limited precipitation that
falls in that area and averages only about
40 cm y-1 (16 in yr-1). Crop residues left
on the soil surface reduced evaporation
from the soil and refraining from tillage decreased the stirring action, which
repeatedly exposes more of the soil water
to evaporation. Reduced evaporation
leaves more of the precipitation in the soil,
where it penetrates deeper and keeps the
Jan/feb 2011—vol. 66, no. 1
Copyright © 2011 Soil and Water Conservation Society. All rights reserved.
Journal of Soil and Water Conservation 66(1):13A-17A www.swcs.org
rops grow by opening their stomata, which allow CO2 to enter
their leaves, where CO2 and
water can be photosynthesized into
carbohydrates using the sun’s energy. Photosynthesis occurs in the light only if CO2
continues to diffuse from the atmosphere
into the interior of the leaves. However,
stomata cannot remain open for CO2 diffusion if water is not continually supplied
to the stomata to replenish the water these
cells lose via transpiration. If the water flux
from the soil is limited under drought conditions, stomata initiate closure and crop
growth decreases. The soil profile is the
critical storage reservoir, which can absorb
and hold the rainfall until it is needed by
the crop. The amount of rainfall that can
be absorbed, stored, and made available for
crop use depends on the porosity and texture of the soil and depth to which crop
roots penetrate the soil.
13A
Table 1
Depths of rooting and Lumbricus terrestris (L.t.) activity under tilled and long-term
no-till management.
Place
Management
Rooting depth Depth ratio of L.t. burrows
(cm)
no-till/tilled depth (cm)
Middens
(per m2)
1988
Mandan, ND
No-till wheat
Tilled wheat
112 87
1.30
0
0
0
0
1989
Mandan, ND
No-till wheat
Tilled wheat
89
69
1.29
0
0
0
0
1990
Mandan, ND
No-till wheat
Tilled wheat
76
66
1.15
0
0
0
0
1992
Mandan, ND
No-till sunflowers 193
Tilled sunflowers 143
1.36
0
0
0
0
2008
Oshkosh, WI
No-till wheat
150 143
24
Tilled wheat
75
2.00
0
0
2009
Oshkosh, WI
No-till corn
Tilled corn
142
74
1.29
143
0
36
0
2009
Omro, WI
No-till corn
Tilled corn
104
56
1.86
102
0
13
0
2009
Oshkosh, WI
No-till corn
Tilled corn
122
64
1.91
121
0
26
0
2009
Oshkosh, WI
No-till corn
Tilled corn
131
67
1.96
128
0
24
0
soil softer, thereby enabling deeper penetration by the roots and facilitating more
vigorous growth of the whole plant. In
these studies, depth of rooting throughout
the growing season was monitored using
a camera inserted in clear acrylic tubes,
which had been inserted at 45º in the root
zones prior to planting the crops.
To determine maximum rooting depth
in fields of tilled and no-tilled corn in the
vicinity of Oshkosh, Wisconsin, where
precipitation averages about 69 cm y-1
(27 in yr-1), we dug pits in the soil when
the crop had matured. Chunks of this clay
loam soil, cut out of the soil profile with
hand shovels, were broken open by hand,
revealing the presence or absence of roots,
worms, and macropores. Since many of
the lower roots are only a small fraction of
a millimeter in diameter, this determination required careful examination. Depths
to which there had been penetration by
big L.t. earthworms were more easily
determined since their holes are about 5
mm (0.2 in) in diameter. In the long-term
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Jan/feb 2011—vol. 66, no. 1
no-till soils, in which there were generally
substantial populations (10 to 40 m-2 [8 to
33 yd-2]) of these worms, most of the burrows extend vertically to depths of 1 to
2 m (40 to 80 in) below the soil surface.
Their holes do not generally extend below
the depth to which there have been roots
in these subsoils. This was expected based
on observations, such as those of Kemper
et al. (1988), that these worms do not
enter subsoils with generally low organic
matter unless there is a source of organic
matter along the way from which they can
gain energy that they require to continue
their activity.
Another relevant interaction of the
worm and root holes noted in these
tough, high clay content Wisconsin soils
was that about a fifth of the worm holes
were inhabited by one, two, or occasionally more crop roots. Having found their
way into these holes, the roots apparently
grow rapidly down them, encountering
little resistance, compared to that in the
surrounding tough, high clay soils.
DEEPER ROOTING ASSOCIATED WITH
EARTHWORMS
The substantially greater increase in rooting
depth associated with the large and active
populations of earthworms under longterm no-till management in Wisconsin soils
is consistent with observations of Doyle B.
Peters near Champaign, Illinois (personal
communication, 1968). Peters found soybean roots down to 100 cm (40 in) depth
in soils where earthworms had been active,
compared to depths of only about 60 cm
(24 in) where there had been no observable earthworm activity. This consistent
correlation between depths of rooting and
earthworm burrows suggests a synergistic relation between these factors. Deeper
decaying roots provide energy needed by
earthworms to go deeper to reach more
optimum temperatures and survive during the winter. The relatively vertical and
persistent L.t. burrows allow many roots to
bypass much of the resistance of these tight
clay soils and grow deeper.
This synergistic coupling between
increasing depths of earthworm burrows
and rooting is not a “quick fix” for achieving deeper rooting.The roots are generally
not found more than a few centimeters
deeper than the earthworm burrows,
which limits the annual increase in rooting
depth to a few centimeters.This is probably
one of the reasons for the slow improvement of yields under no-till management,
which often require a decade to be fully
significant and continue to improve during the second and third decades (Ismail
et al. 1994).
journal of soil and water conservation
Copyright © 2011 Soil and Water Conservation Society. All rights reserved.
Journal of Soil and Water Conservation 66(1):13A-17A www.swcs.org
Date
Paired comparisons, made of rooting
depths in adjacent fields under long-term
no-till management and tilled management
in clay loams near Oshkosh,Wisconsin, are
summarized in the bottom half of table 1.
Rooting depths under no-till were 86% to
100% greater than those under tillage in
these soils.
Merrill et al. (1996) report that there
were no Lumbricus-terrestris observed in
the Mandan, North Dakota, studies, and
we concluded that there was not enough
precipitation (averaging less than 40 cm y-1
[16 in yr-1] in those years) to sustain these
worms in those drier soils.
journal of soil and water conservation
Height of tallest extended corn leaf or tassel (cm)
Growth rates as affected by drainage management and rainfall.
35
300
30
250
25
200
20
150
15
100
10
50
5
0
0
June 1 June 11 June 21 July 1 July 11 July 21 July 31 Aug 10 Aug 20 Aug 30
Date
Legend
Tilled with low water table
No-till with low water table
No-till with high water table
Precipitation
Table 2
Heights, rooting depths, and yields of corn in tilled and no-till areas.
Area
Final height
(cm)
Root depth
(cm)
Grain yield
(bu/ac)
(t/ha)
Tilled #1
Tilled #2
No-till #1*
No-till #2
230
232
222
242
58
69
122
132
160 164
186
205
10
10.3
11.7
12.9
* Where water table was high and corn appeared to be nitrogen deficient until July 22nd.
that were directly across the road from
each other. Further consultation with the
owners regarding these fields revealed,
however, that an old tile drain was still
functioning in this section of the tilled
field, which, combined with less surface
residue, allowed the soil to dry sufficiently
to plant on May 4th on the tilled side of
the road. On the no-till side of the road,
the soil did not become dry enough to
plant until May 20th. The water table was
only 60 cm (2 ft) below the surface on
the undrained no-till side in this area, and
the soil was considered too wet to inject
dissolved N fertilizer as was done on the
Copyright © 2011 Soil and Water Conservation Society. All rights reserved.
Journal of Soil and Water Conservation 66(1):13A-17A www.swcs.org
GROWTH AND YIELD INCREASES FROM
DEEPER ROOTING AND ACCESS TO
MORE PROFILE WATER
To determine whether no-till management was making significantly more water
available by enabling roots to grow deeper
and draw more water from the soil profile, growth was monitored on tilled and
long-term no-till fields during the growing season of 2009. Hybrid corn (DeKalb
4837) was planted on the tilled field on
May 4th and on an adjacent long-term
no-till field (Midwest 69575VT3) on May
20th.Wood dowels were pounded into the
soil near each of six emerging corn plants
in each of two adjacent rows in each of
two areas in each field. Heights of the tallest extended corn leafs, or tassels, were
measured from these dowels on the dates
indicated in figure 1, where the average
heights are plotted for each area. Water
contents and yields of corn grain were
determined in October. Maximum depths
of rooting were also determined, using the
procedure outlined earlier for Wisconsin
soils, in all four of these areas, and a summary of these measurements is presented
in table 2.
As a result of earlier planting and daytime soil temperature averaging about 2ºC
higher, corn started growing earlier on
the tilled areas than on the no-till areas.
This lag in the no-till field was particularly apparent when the comparison was
made between the tilled and no-till fields
Figure 1
Precipitation (mm)
These earthworm burrows in subsoil
can persist for years. We found many of
them in the summer of 2009 in soils that
were taken out of perennial hay production 15 years ago and have been tilled
regularly since that time, which has practically eliminated the L.t. population. Many
sections of the old L.t. burrows still exist in
the subsoil and some of them are still serving as passageways for growing corn roots,
which are still reaching depths of about
100 cm (40 in) compared to 56 to 75 cm
(22 to 30 in) on nearby fields which have
had continuous tillage for several decades.
Using corn rows 38 cm (15 in) apart and
applying 193 kg of nitrogen (N) ha-1 (173
lb ac-1) resulted in corn grain yields near
15 t ha-1 (240 bu ac-1) on this field with
roots extending down to 100 cm (40 in).
tilled side (115 kg N ha-1 [102 lb ac-1]) on
June 10th. Dry urea was broadcast onto
the whole no-till field at the rate of 85 kg
N ha-1 (75 lb ac-1) on June 27th.
The south end of the no-till field was
about 3 m (10 ft) higher than the north
end, and the water table there was 120 cm
(4 ft) below the soil surface. Corn planted
on May 20th grew rapidly in the area with
the lower water table. Heights of corn in
all three areas of the fields are shown in figure 1. Practically negligible rain from June
21st through July 21st forced the corn on
these fields to depend on reachable stored
profile water during the week before the
Jan/feb 2011—vol. 66, no. 1
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Jan/feb 2011—vol. 66, no. 1
included that information in table 2.Yields
on the tilled corn plots were in about the
midrange for Wisconsin corn, where 11 kg
of starter N ha-1 (10 lb ac-1) is applied at
seeding time and another 114 kg of N ha-1
(100 lb ac-1) is applied during June.
This study indicates that a major portion
of the yield reduction due to short-term
drought, as occurred in the summer of
2009, can be avoided on this tough, high
clay content soil by long-term use of
no-till management as this management
has achieved a substantial population of
Lumbricus terrestris and associated deep
rooting of the crops.
SIMULATED INCREASES IN YIELDS
DUE TO DEEPER ROOTING BASED
ON CLIMATES RECORDED IN PAST
GROWING SEASONS
Growth rates indicated in figure 1 show
that during this particular drought period,
growth in a no-till corn field with deeper
rooting was maintained better than in an
adjacent tilled field with shallower rooting. Whether this response has economic
significance depends on the length and
frequency of such droughts. Fortunately,
the weather bureau has recorded rainfall,
temperature, and solar radiation for several
decades at many locations.
Muchow and Sinclair (1991) developed a comparatively simple model to
simulate growth and yield of corn, when
subjected to water deficit conditions. Key
inputs in this model were these climatic
factors, recorded by the bureau, and the
maximum depths to which the roots could
grow. Deeper rooting provides a larger
reservoir for storage of water from previous rain, which can be used during later
season droughts.
Sinclair (1994) compared the impact
of differing corn rooting depths over 20
growing seasons at Columbia, Missouri,
Holly Springs, Mississippi, and Athens,
Georgia. Increasing the simulated maximum rooting depth from 60 to 100 cm (24
to 40 in) resulted in average yield increases
of 100%, 64%, and 55% at the three locations, respectively. Most of the mean yield
increases resulted from increases in yield
in the driest growing seasons rather than
from increases in the wetter seasons.
Corn yield was simulated for the rainfall,
solar radiation, and temperatures, which
occurred during 17 growing seasons in
Madison, Wisconsin, for rooting depths
varying from 70 to 150 cm (28 to 60 in)
(figure 2). The mean grain yield across the
17 years for the two extreme depths was
9.5 and 12.2 t ha-1 (179 to 231 bu ac-1) at
Figure 2
Mean corn yields predicted from solar radiation, temperature, and rainfall occurring
during 17 years at Madison, Wisconsin, assuming indicated rooting depths.
Simulated mean corn yields (t ha-1)
14
13
12
11
10
9
8
60
70
80
90
100
110
120
130
140
150
160
Rooting depth (cm)
journal of soil and water conservation
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Journal of Soil and Water Conservation 66(1):13A-17A www.swcs.org
rain on July 22nd. With the maximum
rooting depth under no-till almost twice
as great as that under tillage, it is not surprising to see the corn on the no-till fields
sustaining higher growth rates than on the
tilled fields during that driest week (July
14th to 21st).
Corn on the high water table end of the
no-till field, whose early season growth
was comparatively delayed by colder and
wetter soil, was showing a lot of yellow
hue in its leaves during the first two weeks
of July and was 50 cm (20 in) shorter than
the corn in the other two areas. When
25 mm (1 in) of rain fell on July 22nd, it
apparently enabled corn in all three areas
of the fields to resume full-scale photosynthesis during the daylight hours. However,
the greatest increase in growth rate was
observed on the high water table end of
the no-till field (table 2). This increased
growth rate, coupled with significantly
darker green color developing in the leaves
at this time, led us to suspect that this rain
probably completed the transformations
and mobilization of the urea, which had
been broadcast on this soil on June 27th,
to highly mobile nitrate, which moved
with the rain water into the root zone and
enabled these yellowed corn plants to take
up the nitrogen that they needed to overcome this growth inhibiting deficiency.
During the month from June 21st to
July 21st, the absence of rain apparently
negated the process by which broadcast
urea is usually moved down and into the
root zone. In this field with its shallow
water table, water was moving toward the
surface by capillarity, evaporating there at
the surface during the early summer, and
was probably keeping the surface-applied
nitrogen near the surface and away from
the corn roots. Rapid recovery of these
N deficient plants after the July 22nd rain
enabled them to produce 11.7 t ha-1 (186
bu ac-1) of corn grain in 2009, which was
1.4 t ha-1 (22 bu ac-1) more than was produced on the earlier planted tilled field
across the road.
To expand our information on late
season growth and yield of tilled corn for
these comparisons, we selected an additional pair of rows about 60 m (200 ft)
east of tilled plot #1, measured the corn
height, rooting depth, and grain yield and
CONCLUSION
Insufficient water is the most common
factor limiting crop production. In some
areas, irrigation systems can be developed
to help relieve that deficiency. However
irrigation is a costly input to the production system, and in many areas the water is
not available. Most of the water used to fill
crop water needs during extended periods
between precipitation events is water stored
in the soil profiles. The amount of water
that a crop can draw from the soil profile is
directly dependent on the depth to which
that crop’s roots penetrate the soil. Longterm no-till management of soils generally
increases the depth of crop rooting in soils.
Measured increases have ranged from 15%
to 36 % in North Dakota soils that were
receiving about 40 cm y-1 (16 in yr-1) of
precipitation and where an L.t. population had not developed under the no-till
management. In Wisconsin, where precipitation averaged in the 60 to 70 cm y-1 (24
to 28 in yr-1) range, and water table levels were appreciably below freezing levels
during the winter, L.t. populations ranged
from 10 to 40 m-2 (8 to 33 yd-2) in soils
under long-term no-till, and their burrows
helped the roots get down 86% to 100%
deeper than in adjacent tilled fields. Access
journal of soil and water conservation
to this additional water stored in the soil
profile enables crops to continue growth
better during drought periods, resulting in
better drought-year yields.
Conservation of our resources has been
a worthy goal of our society since its
inception. However, as global population
continues to increase, it is apparent that
conservation of our current resources will
not be sufficient to enable us to feed future
multitudes. Consequently, it is heartening
to find that some of our production systems,
such as no-till, are able to increase organic
matter contents of our soils (Reicosky
et al. 1995) and the ability of our crops
to use existing precipitation to produce
higher yields. Such “enhancement” of our
resources will be necessary to provide sufficient food, clothing, and energy to fill the
needs of future generations.
REFERENCES
Edwards, W.M., and L.D. Norton. 1986. Effect of
macropores on filtration into non-tilled soil.
Transactions of the 13th Congress of International
Soil Science 5:47-48.
Ismail, I., R.L. Blevins and W.W. Frye. 1994. Longterm no-tillage effects on soil properties and
continuous corn yields. Soil Science Society of
America Journal 58:194-198.
Kemper, W.D., P. Jolley, and R.C. Rosenau. 1988. Soil
management to prevent earthworms from riddling irrigation ditch banks. Irrigation Science
9:79-87.
Merrill, S.D., A.L. Black, and A. Bauer. 1996.
Conservation tillage affects root growth of dryland spring wheat under drought. Soil Science
Society of America 60:575-583.
Muchow, R.C., and T.R. Sinclair. 1991. Water deficit
effects on maize yields modeled under current
and “greenhouse” climates. Agronomy Journal
83:1052-1059.
Reicosky, D.C., W.D. Kemper, G.W. Langdale, C.L.
Douglas, Jr., and P.E. Rasmussen. 1995. Soil
organic matter changes resulting from tillage and
biomass production. Journal of Soil and Water
Conservation 50(3):253-261.
Sinclair,T.R. 1994. Limits to crop yield. In Physiology
and Determination of Crop Yield, 509-532.
Madison, WI: American Society of Agronomy.
Wolkowski, R.P. 2007. Adjusting tillage practices
in a corn-soybean rotation. In Proceedings
of the 2007 Wisconsin Fertilizer, Aglime, and
Pest Management Conference, University of
Wisconsin, Madison, Wisconsin, 46:182-188.
Jan/feb 2011—vol. 66, no. 1
Copyright © 2011 Soil and Water Conservation Society. All rights reserved.
Journal of Soil and Water Conservation 66(1):13A-17A www.swcs.org
15.5% moisture, constituting a mean yield
increase of 29% expected from increasing rooting depth from 70 to 150 cm.
Although the climate tended to be moister
in this northern portion of the Corn Belt,
additional rooting depth still substantially
increased yield. In this Wisconsin area, the
simulated yield increases due to deeper
rooting were more consistent across years
than they were in the more southern states.
In the wettest year, the simulated yield
increase from deeper rooting was 14%,
and in the two driest years it was 58% and
70%. However, in the years with intermediate rainfall, the yield increases were all in
the range from 25% to 36%. Overall, these
simulation results, based on past climatic
data, indicate that corn yields will generally be substantially increased as a result of
the deeper rooting associated with burrowing of Lumbricus terrestris and similar
earthworms, whose populations develop
under long-term no-till management in
moist well-drained soils.
17A