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Agronomic Row Crops: The Farmers
Thompson Farm Trials Confirm Efficiencies of Covers, Hoes,
Cultivators
 Dick
& Sharon Thompson
Boone, Iowa
 300
acres
corn,
soybeans, oats, hay, cover crops
ridge-till
for row crops
slightly
rolling fields in central Iowa
Weed management highlights
Strategies: early weeds managed to suppress late-germinating
weeds... no preplant tillage... increased plant population... 36"
rows... fine-tuned cover-crops
Tools: customized ridge-till planter... high-residue
rotary hoe... high-residue cultivator... guidance mirror
Dick and Sharon Thompson and their son,
Rex, didn't just write the book on sustainable weed control--they
update it with improvements every year. A high-residue cultivator
and high-residue rotary hoe are prominent among other sustainable
tools and practices in the scientific on-farm testing they have
conducted since 1985. (For their latest report, send $10 to Thompson
On-Farm Report, 2035-190th Street, Boone IA 50036-7423.)
No part of their cropping system exists long without being scrutinized
for improvement. They still use cover crops, but have long ago moved
away from fall-broadcast mixtures of winter rye and hairy vetch.
Vetch posed too many management problems come spring.
For cover crops ahead of soybeans, their experiments found the
most weed-suppressing benefit from rye alone, drilled at 20 pounds
per acre only on the ridge top--two rows, 6 inches apart, each 3
inches from the crop row. A ridge-till planter can remove spring
growth of 8 to 12 inches. Taller rye can be knocked down with a
stalk chopper. (See "Cover Crops")
Corn's need for early nitrogen and moisture means rye is not a
good cover crop choice for corn planted on ridges, the Thompsons
found. Rather, they overseed oats at 2 bushels per acre with a high-clearance
tractor at leaf-yellowing of soybeans--usually in late August. Freezing
weather kills the oats, but stalks remain on the surface to protect
the soil from spring erosion.
When they plant corn into a flat field following hay, however,
they spread rye through Gandy seed boxes during fall plowing of
the hay field as they incorporate strawy manure. The greater weed-suppressive
effect of rye is needed for this transition, and standard spring
soil preparation allows a way to control the rye that is not available
in their no-herbicide, ridge-till-only system. Field
cultivators kill most rye at the 6- to 8-inch stage,
with scratchers dragging behind to bring the residue to the surface.
After waiting about a week for the disturbed weed seeds to germinate,
a second field cultivation takes out almost all the rest of the
rye. At final weed cultivation with his maximum-residue,
single-sweep cultivator, Thompson attaches ridging
wings just above sweeps to divert soil into the row
to create the elevated ridges that will be used the next several
seasons.
"Crop rotation is the key," says Dick Thompson, who tries to maximize
soil-building and weed-fighting benefits from the farm's mixed enterprises.
Components include hogs, beef cattle and livestock manure, with
aerobic digestion of municipal biosolids. The five-year crop sequence
is corn-soybeans-corn-oats-hay (legume/grass mix).
Weed populations take a beating from this varied sequence of soil
environments, preventing annuals and perennials from strengthening
their populations. Existing weed seeds sprout between rows or between
plantings--the places and times when light tillage or mowing can
control them. Multiple cuttings in hay years knocks back species
that thrive in undisturbed soil. The winter cover crops of rye and
oats are selected and managed to mesh precisely with the intended
crops to follow.
For row crops, Thompson uses ridge tillage, a system that plants
rows in the middle of raised soil areas--ridges--that dry out and
warm up faster in spring. By planting into the same row area each
year, the system controls implement traffic. Ridge-till also can
cut labor and fuel costs compared with conventional tillage because
there is no pre-plant tillage and less soil is disturbed.
Ridge-till's permanent rows and necessary ridge-restoring cultivation
provide the bridge from broadcast spraying to herbicide banding
for some farmers. The next reduction can be to lower material rates
within the bands. For Thompson and others, ridge-till's weed seed
movement into the row middles at planting and faster, closer cultivation
have allowed him to virtually eliminate chemical weed controls in
most years. In any tillage regime, straighter rows can translate
into easier, more efficient mechanical weed control with a lower
risk of crop damage.
Thompson advises all farmers to refine management through their
own on-farm testing. He offers these cumulative findings for evaluation:
Manage early weeds to control later weeds. Thompson
claims this is the "best-kept secret in agriculture." He observes
that the first weeds prevent more extensive germination of later-developing
weeds. This may result from compounds released from roots or other
factors such as shading and moisture competition. He regards early
weeds as a natural cover crop. Despite their potential for good,
early weeds need to be controlled in the row at planting with timely
rotary hoeing or at first cultivation while they are small enough
to be easily managed and before quick-maturing species go to seed.
Thompson's row-cleaning, ridge-till planter moves weed seeds and
cover-crop residue into row middles as a mulch that protects soil
and stifles weed development. (See "Ridge
Till Planters Suppress In-Row Weeds")
Select a planter that fluffs loose soil over firmly
planted crop seed. This leaves crops in a good environment
for germination but puts weed seeds in a poor environment for getting
started. Be aware that packer wheels working on the surface or trailing
scratchers improve weed germination rates, he warns.
Plant crops thicker for quicker in-row shading
and to allow for some reduction in plant population from mechanical
tillage. Twelve soybean seeds per foot and corn seed at 6-inch spacings
work best, Dick Thompson finds.
Rotary hoe before and after crop emergence.
He keeps a close eye on planted corn, waiting for seeds to sprout
before using his M&W Gear high-residue rotary hoe--but
he faithfully hoes soybeans three days after planting, weather permitting.
The different approaches result in the same end: he hoes both crops
just before emergence thanks to the longer time corn usually waits
in cooler soil.
“Managing weeds with crop rotation, ridge tillage and steel is
$54 per acre more profitable for us than with broadcast herbicides
and mulch tillage.” — Dick Thompson
"You have to get off the tractor to check the hoe's penetration,
weed kill and crop response," says Thompson. He looks for crop seed
disruption or seedling damage. "Then I know how fast to drive and
how deep to go." These preemergence passes are shallow (about an
inch) and fast. "Fifteen miles per hour is about as fast as I can
hang on," he admits. Extreme weed pressure justifies an immediate
second trip, which Thompson does by half-lapping the previous round.
He waits about a week before hoeing a second time. At this point,
corn is at about the two leaf stage (the third leaf is just beginning
to emerge from the whorl) and soybeans have true leaves. These early
"broadcast" tillage passes are important to suppress weeds when
they are easiest to kill, and especially to control in-row weeds.
His M&W Gear high-residue
rotary hoe handles residue well. Thompson believes
that hoes need at least 20 inches between front and rear shafts
to handle heavy residue. Rotary hoeing returned an average of $16.20
per acre more than even banded herbicides did in a three-year
weed-control comparison, Thompson reports.
Outfit your cultivator for young crops--and
have it ready to run! His standard practices at first cultivation
include
- Disk hillers with the leading edge angled
into the row and cupped forward to make a cut as wide as possible
that still moves soil away from the row. The hillers are set 5
inches apart--but even "tighter on the row that I watch," explains
Thompson, to narrow his margin of error.
- A "Culti-Vision" rearview mirror. This
hooded, adjustable guidance aid is mounted on a bracket attached
to the tractor frame just behind the front axle. It is aligned
so the driver can see exactly where the hillers are running next
to the crop. The mirror improves the driver's control enough to
run about 3.5 mph at a stage when crop plants are too small to
activate the sensing wands of an electronic guidance
system. By also using a wide-angle, rear-view mirror inside the
cab, Thompson can scan all four rows without turning around.
"Guys who use herbicides can afford to wait for four-inch corn
that will activate guidance system wands. But those of us who are
all-mechanical have to be out there earlier to stay ahead," he says.
One species he particularly targets for early control is lambsquarter.
Once the tap-rooted competitor is 6 inches tall, it becomes difficult
to kill with a cultivator. Broadleaf weeds that have less of a tap
root are easier to control when they are taller.
Use of 26-inch one-piece
sweeps in 36-inch row spacings. "I need to be able
to increase the pitch to get some soil-turning action," Thompson
finds. "The flat, narrow surface of point-and-share
sweeps basically undercuts weeds. I want to be harder
on my weeds than that."
Metal tent shields
with 18-inch rear extensions dragging in the soil. The shield fronts
stay down if rows are clean--to keep out fresh soil with its newly
exposed weed seeds--but are raised slightly to allow loose soil
to flow in if enough small, in-row weeds are threatening. The rear
extensions add extra stability and crop protection. At second cultivation,
he replaces the tents with open-top, flat
panel shields to avoid bending crops.
Stopping, dismounting and stooping low to
inspect crops and weeds. Where he plans a hay crop and doesn't need
ridges the coming year, Thompson does a second cultivation with
wide sweeps before crops are a foot tall. He changes the
angle of the disk hillers to throw soil toward the crop
row, and moves them farther away from the row to avoid throwing
soil around the plants. In soybeans, this prevents damage to lower
pods and keeps mounded soil from interfering with harvest. In corn
it limits root pruning that can hurt yield. His tests show that
ridging in fall after corn harvest and removal of stalks can increase
weed numbers in the following year's soybeans.
In wet seasons when crops are much more than a foot tall before
he can make a second pass, Thompson uses a 14-inch sweep without
ridging wings to avoid cutting crop roots.
Where he wants to build a ridge, Thompson begins the second cultivation
with 14-inch sweeps after crops are a foot high. At that
point the plants can tolerate contact by flowing soil that smothers
in-row weeds. He moves the disk hillers to the row middles and turns
them to push soil into the row. A "butterfly" ridging
wing mounted on the shank behind each sweep diverts
soil from the middles to the row ridge, smothering in-row weeds.
Two sets of open-top row shields ride several inches off the soil
surface next to the row to protect crop stalks and leaves.
Because bigger plants block his view of the hillers via the Culti-Vision
mirror, Thompson removes it and uses his pivot-type automatic
guidance system as crops mature. The electronic-hydraulic
unit guides the implement to keep it in alignment with the row.
Guidance greatly eases driver stress and allows Thompson to travel
about 6 mph.
Night cultivation and tilling has yet to show consistent benefits
in USDA-supervised tests on Thompson's farm. In other trials, the
practice has reduced post-tillage germination of small-seeded broadleaf
weeds. As part of his on-farm research in '96 with researchers from
the National Soil Tilth Laboratory in Ames, he used night-vision
goggles for nocturnal ridge-till planting. The goal is to deprive
light-activated weed seeds the illumination necessary to trigger
germination.
Improved implements and mechanical techniques hold the best opportunities
for making weed management more sustainable, says Thompson. "If
you use herbicides and still don't control weeds, you're building
herbicide resistance. If you do control your target weed, you get
weed-species succession and end up with weeds that are harder to
control." He can trace a troublesome weed progression from horseweed
to foxtail to velvetleaf during his own farm's "chemical era."
In '95, the Thompsons and other farmers who successfully practice
integrated weed control with negligible herbicides formally described
their systems to gatherings of weed management professionals. From
those sessions, Dick Thompson sees a new appreciation for the importance
of "alternative" practices.
"Weed scientists are finally taking field ecology seriously, talking
about 'managing' weeds rather than 'controlling' them, and saying
herbicides should be the last resort. I think they're on the right
track."
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