Posted January 17,
2008: Delayed planting, a higher seeding rate and
super-winter-hardy hairy vetch varieties can combine to produce
top organic no-till corn yields, allowing producers who carefully
track cutworms to beat these bugs.
These findings from fields at The Rodale Institute in 2007
add new understanding of how to increase the positive impact
of the Institute’s roller-crimper. This simple, rugged
implement is a smart-technology bridge in two critical spheres:
for organic farmers to move into no-till (saving tillage,
labor, fuel and time in field prep and mechanical weed management);
and for non-organic no-tillers (to add cover crops to cut
their costs for purchased fertility and weed management, while
increasing soil carbon additions).
Records show 2006 was the breakthrough year for our organic
no-till yields of corn. (See
an overview here with details
here on the conditions and management that resulted in
a yield report of 146 bu/ac.)
We realized even better yields in 2007, but also learned
some valuable lessons about the interplay of cover-crop survival,
corn-stand numbers and corn variety day-length variations.
So here’s the 2007 story, starting from the beginning:
cover-crop planting the previous fall.
First thing: cover-crop hairy vetch
In late summer 2006 the intended corn field was prepared
with clean tillage (moldboard plowing, disking and cultipacking)
and planted to a combination of hairy vetch (Vicia villosa)
and spring oats (Avena sativa), drilled on September
8 at 18.5 lbs/ac and 47.5 lbs/ac, respectively.
In this trial we looked at hairy vetch with two seed-tag
origins. One was purchased through Ernst Conservation Seeds
with a seed tag origin of Nebraska and a 74-percent germination
rate; the other was from our local farm-supply store (F.M.
Brown, Fleetwood, Pennsylvania) and had a seed tag origin
of Oregon, labeled “EarlyCover” with a germination
rate of 85 percent.
The winter of 2006-2007 began mildly enough; the fall growth
of both hairy vetch types produced about 1,000 lbs/ac of biomass
(dry weight) before going dormant for winter. Then in February,
the “EarlyCover” hairy vetch took a dive. A genetic
cost for its prized early blooming trait—which has strong
economic benefits in spring—seems to be lessened winter
Conditions were harsh, and we had little snow cover to provide
insulation. Early February temperatures dropped as low as
O°F, and in mid-February we recorded low temps of 4°F.
Temperatures warmed up above freezing for a short spell, but
dipped as low as 0°F again by mid-March.
on many influences
temperatures during the winter period can cause
serious stand losses in northern states, even in
southeastern Pennsylvania. Winter survival of legume
cover crops such as hairy vetch can be one of the
most important determinants of successful biomass
production the following spring (and of subsequent
crop yields during the growing season).
Cover-crop plant losses during the winter are
usually the result of low temperatures in association
with moisture in or on the soil or in the plant
itself, since in the absence of a snow buffer
the plant tissue is directly exposed to the surrounding
frost and ice. The crowns and roots of even the
most cold-resistant forages cannot stand direct
exposure for very long to temperatures as low
as 5°F to 15°F without injury or death.
We typically plant spring oats with hairy vetch, both to
cover the soil quickly after harvest in the fall (since the
hairy vetch establishes more slowly) and to provide sheltering
insulation to the hairy vetch and soil. In the winter of 2006-2007,
the dead oat residue did not provide enough insulating effect
for the “EarlyCover” hairy vetch. Since this variety
puts on fall growth more rapidly than other vetches, that
extra green matter makes it especially vulnerable to cold
weather and in need of this sheltering residue. Our “EarlyCover”
didn’t survive the Arctic blasts and left us with insufficient
cover-crop biomass to roll in spring 2007 in those plots.
Fortunately, we had mixed in plots with the Nebraska-type
hairy vetch, which turned out to be very winter hardy. It
produced adequate biomass required for a rolled weed-suppressing
mat for the following crop of organic no-till corn.
We began evaluating the hairy vetch stands for bloom and
biomass in May 2007. One of our main objectives for the coming
no-till corn trial was to evaluate four dates of rolling/planting
of the no-till corn.
The first roll-and-plant date was May 30—delayed from
normal local planting to allow greater vetch maturity, biomass
and fertility, but early in the vetch season—with successive
rolling and plantings taking place weekly on June 7, June
14, and finally on June 21. Bloom ratings were at 50 to 60
percent on May 7; 60 to 70 percent on June 7; and 100 percent
on June 14. The last planting date was very late for our location
in southeast Pennsylvania where conventional no-till corn
planting typically takes place in early May.
Critical note: The major consideration
in timing the mechanical killing of the hairy vetch cover
crop is bloom stage. The vetch should be at full-bloom stage
before rolling, which will ensure adequate kill by the roller’s
crimping action and will also ensure that the hairy vetch
will be mature enough that it supplies adequate biomass for
both weed control and the nitrogen needed for the corn crop.
The biomass making up the rolled mat restrains the weeds until
the corn can start to grow enough to form a leafy canopy in
the field, shading out weeds.
With this trial we wanted to compare the effect of the killing
time of hairy vetch on weeds, pests and yield.
Dodging cutworm damage with timing
The black cutworm (Agrotis ipsilon)—the cutworm
moth in its caterpillar stage—has been a major pest
of our organic no-till corn in past years. This moth is also
called “Dark Sword-grass.” How much damage they
do depends on the stage of corn development and local environmental
conditions. The larvae cut off many more plants than they
consume—and they consume a lot.
While some cutworms may develop from overwintering pupae
or adult moths, most come from adult moths blown into the
area with storm fronts during April and May. Moths fall out
of the sky, laying eggs where they land. We see eggs on grasses,
broadleaf weeds, crop residues and on our hairy vetch cover
crop in the early spring, usually before the corn is planted.
For many insects, no-till agriculture represents a major
positive change in their immediate ecosystem. Full tillage
typical of organic agriculture is extremely disruptive of
soil-insect habitat and produces high mortality of many of
the crop pests—including these moths. Generally organic
no-till ensures greater survival of many pests as well as
many beneficial-insect species that remain within the no-till
field or move to surrounding fields or crops.
Black cutworms are a significant threat to the young corn
crop in Pennsylvania. They produce more than one generation
of offspring per year, but it’s the first generation
that tends to cause the most significant damage to corn.
Seed corn producers rate maturity on the number of equivalent
growing degree days (GDDs) or heat units. The most common
formula for calculating GDD averages the maximum temperature
plus the minimum temperature for the day, minus 50. (Note:
86°F is the highest temperature recorded, even if the
temperature exceeds 86°F.)
GDD units for the black cutworm are calculated in the same
way. In Pennsylvania the black cut worm requires between 200
to 300 heat units to develop from an egg to the fourth-instar
stage, which is the stage when the larvae begin cutting corn
seedlings. The onset of this damage—which lasts for
another 400 to 500 accumulated GDDs—can be accurately
predicted to guide planting decisions.
In Pennsylvania the cutworm spends about one month in the
larval stage, during which they can severely reduce the stand
of corn plants by cutting them off at or just below the soil
surface. We have lost entire fields to cutworm damage. In
the 2006 trial, we discovered many cutworm larvae in early
June and decided to delay corn planting a week, until June
9. We therefore managed to avoid the peak of the cutworm damage.
The design of the 2007 trial with the four weekly planting
dates allowed us to quantify the corn plant population decrease
due to the cutworm damage in the period of May 30 to June
The graph below shows the relation of planting date to corn-plant
population. Fields on all four dates were planted with a rate
of 36,624 seeds per acre at 95 percent germination, which
would ideally translate into 34,793 plants per acre. I purposely
increased seeding rates this year in an effort to increase
the final stand of corn after loss to cutworm damage and to
compensate for other factors, including more-challenging seed
placement in the no-till system.
The first planting date had a stand of 15,616 plants per
acre. The cutworm damage was peaking during the second planting
date and we experienced the largest decrease, with a stand
of only 7,569 plants per acre. As the planting date got later
in June, the cutworm damage decreased and stands improved
dramatically. Populations for the third and fourth planting
dates were 27,998 and 29,991 plants per acre, respectively.
This was a result of the larvae maturing out of their cutting
stage and growing into moths.
Farmers growing no-till corn realize it’s all about
achieving a good stand. In the no-till roller/crimper system,
proper planter modification is absolutely necessary to:
- Cut through the heavy mat of a living, rolled cover
- Place seeds at the proper depth.
- Provide good seed-to-soil contact.
- Leave as much residue as possible over the row to
in- and near-row weed seed germination.
Weed management in this no-till roller/crimper corn system
depends on the mulching effect of the rolled mat of hairy
vetch and a competitive corn-plant canopy. Early rolling—before
full-bloom—does not adequately kill the hairy vetch,
and some of the rolled cover crop pops back up and continues
to grow, failing to provide desirable weed control. This occurred
with the May 30 and June 7 roll/plant dates.
In addition, the decreased stand of corn from cutworms in
the earlier-rolled hairy vetch led to a sparser canopy from
the corn, reducing its competitive shading effect on the weeds.
The higher corn populations and increased weed suppression
from the later plantings are illustrated in the weed biomass
Corn is a population-sensitive crop. Competitive yields are
dependent on sufficient population, and plant loss is directly
influenced by seeding rate, planter setup and pest damage.
For this year’s trial, I recommended increasing the
seeding rate to 36,000 seeds per acre, up from our previous
32,000 seeding rate. The actual calibrated rate was about
36,624 seeds per acre. We increased the seeding rate with
the goal of offsetting some of the loss due to cutworm damage.
Increased seeding rate and late planting gave us an advantage
over the environmental conditions, enabling us to increase
our stand of corn and produce a satisfactory yield—even
at very late planting dates for this region.
The corn variety we used in this trial was certified-organic
hybrid field corn provided by Blue River Hybrids, which had
a Relative Maturity Rating of 95 (commonly called “95-day
corn”). The graph below shows the yield corresponding
to the four planting dates.
Variety selection, plant population, planting accuracy (influenced
by adding extra weight on planting units and adjusting planter
depth to cut through cover-crop residue) and date of planting
may greatly influence the corn stand in this organic no-till
system. Seeding at higher rates allows for some cutworm loss,
and by planting later we avoid the peak of the damaging cutworm
population, which in turn contributes to a more-competitive
corn stand. Later planting also contributes to quick germination
and vigorous seedling growth because soil and air temperatures
are warmer at the later dates, which also helps to optimize
corn populations and resulting yields.
I was very happy with our 2007 no-till yields. Despite the
late planting, this shows another situation where the “no-till
roller/crimper with cover crops” approach can be integrated
into an organic system as a strategy to reduce tillage, labor,
energy and time—and still produce competitive yields
of field corn.