Abawi, G.S., and T.L. Widmer. 2000. Impact of soil health manage-
Pieters, A.J. 1927. Green Manuring Principles and Practices. New
ment practices on soilborne pathogens, nematodes and root
York: John Wiley.
diseases of vegetable crops. Applied Soil Ecology 15: 37–47.
Power, J.F., ed. 1987. The Role of Legumes in Conservation Tillage
Allison, F.E. 1973. Soil Organic Matter and Its Role in Crop
Systems. Ankeny, IA: Soil Conservation Society of America.
Production. Amsterdam: Elsevier Scientific Publishing. In his
Sarrantonio, M. 1997. Northeast Cover Crop Handbook. Soil
discussion of organic matter replenishment and green manures
Health Series. Kutztown, PA: Rodale Institute.
(pp. 450–451), Allison cites a number of researchers who
Smith, M.S., W.W. Frye, and J.J. Varco. 1987. Legume winter cover
indicate that there is little or no effect of green manures on total
crops. Advances in Soil Science 7: 95–139.
organic matter, even though the supply of active (rapidly decom-
posing) organic matter increases.
Sogbedji, J.M., H.M. van Es, and K.M. Agbeko. 2006. Cover crop-
ping and nutrient management strategies for maize production
Björkman, T., R. Bellinder, R. Hahn, and J. Shail, Jr. 2008. Buck-
in western Africa. Agronomy Journal 98: 883–889.
wheat Cover Crop Handbook. Geneva, NY: Cornell University.
http://www.nysaes.cornell.edu/hort/faculty/bjorkman/cover-
Summers, C.G., J.P. Mitchell, T.S. Prather, and J.J. Stapleton.
crops/pdfs/bwbrochure.pdf.
Sudex cover crops can kill and stunt subsequent tomato, lettuce,
and broccoli transplants through allelopathy. California
Cornell University. Cover Crops for Vegetable Growers. http://
Agriculture 63(2): 35-40.
www.nysaes.cornell.edu/hort/faculty/bjorkman/covercrops/
why.html.
Sustainable Agriculture Network. 2007. Managing Cover Crops
Profitably, 3rd ed. Handbook Series, No. 9. Beltsville, MD:
Hargrove, W.L., ed. 1991. Cover Crops for Clean Water. Ankeny,
USDA Sustainable Agriculture Network. www.sare.org. An
IA: Soil and Water Conservation Society.
excellent source for practical information about cover crops.
MacRae, R.J., and G.R. Mehuys. 1985. The effect of green manur-
Weil, R., and A. Kremen. 2007. Thinking across and beyond disci-
ing on the physical properties of temperate-area soils. Advances
plines to make cover crops pay. Journal of the Science of Food
in Soil Science 3: 71–94.
and Agriculture 87: 551–557.
Miller, P.R., W.L. Graves, W.A. Williams, and B.A. Madson. 1989.
Widmer, T.L., and G.S. Abawi. 2000. Mechanism of suppression of
Cover Crops for California Agriculture. Leaflet 21471. Davis:
Meloidogyne hapla and its damage by a green manure of sudan
University of California, Division of Agriculture and Natural
grass. Plant Disease 84: 562–568.
Resources. This is the reference for the experiment with clover
in California.
112
Building SoilS for Better CropS: SuStainaBle Soil ManageMent
a case study
Peter kenagy
albany, oregon
Peter Kenagy’s rotation provides regular windows of
Kenagy also uses cover crops to capture excess
opportunity to grow cover crops, which he has used
nutrients and silt and prevent them from flowing into
for twenty years to build soil and control weeds on his
the adjacent Willamette River during perennial flooding
farm. Kenagy raises processing vegetables, small grains,
episodes on his low-lying fields. “The more cover crop
cover crop seed, and native grass forbs and seeds on
vegetation you have there, the more silt you catch,” he
320 tillable and 130 riparian acres in Oregon’s fertile
says. Besides sudan grass, he often relies on fall-planted
Willamette Valley.
oats—he uses the variety “Saia,” planted at 30 pounds an
The period following green beans, which are in the
acre—to produce abundant aboveground biomass.
ground just seventy days and come off in July or August,
He has experimented with many different covers,
is a perfect time, Kenagy says, to plant a summer cover
modifying his use of cover crops to fit changes in his
crop like sudan grass, which will grow up to 5 feet tall
cash crop rotation. In addition, practical concerns or
before winter-killing with the first frost. The thick grass
experiences inform his choices of which cover crops
mulch continues to provide a good ground cover when
to use. For example, he no longer plants dwarf essex
he plants corn into it in the spring. Sometimes he plants
rape because it could cause unwanted cross-pollination
sudan grass as a bridge crop between beans and a fall-
with other brassicas. He favors using oats rather than
planted grass crop.
triticale because he’s found the former are more readily
and cheaply available and cause fewer disease problems
when followed by a wheat crop.
Maintaining weed-free fields is especially
Though Kenagy typically plants common vetch to
crucial for Kenagy’s intensive production of
fix nitrogen, he’s searching for another legume that will
native grass forbs and seeds, which are
provide solid cover and boost N levels in the late sum-
mer before fall planting of grass crops.
destined for wetlands mitigation and other
Phaecelia, which overwinters in the Willamette
restoration projects.
Valley, has become one of Kenagy’s preferred covers in
recent years. He plants this small-seeded cover crop at a
“I have a huge gap between one crop and the next,”
rate of 2 to 4 pounds per acre. He says, “You don’t have
says Kenagy. “I have to control weeds during that
to plant the seed too deep, and with a little moisture,
period, which is just one of a number of things a cover
[phaecelia] grows like gangbusters” and is highly effec-
crop does so well.” Maintaining weed-free fields is espe-
tive at suppressing weeds. “It’s easy to kill, pretty much
cially crucial for Kenagy’s intensive production of native
using any method you want. Its biggest attribute is that
grass forbs and seeds, which are destined for wetlands
it breaks down really fast. Barely any effort is required to
mitigation and other restoration projects.
get rid of it.”
113
building soils For better CroPs: sustainable soil ManageMent
“One of the most abusive things farmers do to the soil is till it, and most
do it repeatedly,” Kenagy says. “Strip till does less abuse to the soil, and keeping the residue on top is a much more natural way for it to be handled.”
Reducing the effort required to manage any crop is
no-till methods to plant and manage his cash and cover
a hallmark feature of Kenagy’s operation. “I plan my
crops. For certain crops, such as sweet corn, he uses
rotation by looking at what I’m coming out of and figure
strip-tillage to cut through vegetative residue, which
out the easiest thing to rotate in, so that I don’t have to
disturbs just 6 inches of soil—a mere one-fifth of the soil
do so much,” he says. “ I don’t want to be stuck trying to
surface that is typically plowed with conventional tillage.
till wheat stubble in the fall.” Through his careful choice
(For information about strip tillage, see chapter 16.)
and timing of specific crops, Kenagy is able to till less,
“One of the most abusive things farmers do to the
save money on fuel, and improve soil quality.
soil is till it, and most do it repeatedly,” Kenagy says.
“Part of what’s driving this is logistics,” he says,
“Strip till does less abuse to the soil, and keeping the
describing a field of perennial ryegrass that he recently
residue on top is a much more natural way for it to be
left to break down in the field for a year after it was
handled,” as it is thus mimicking a more natural system.
killed with an herbicide. “The [ryegrass] crowns left
Grassland and forests, he points out, undergo perpetual
good cover while they rotted; this was a good alternative
cycles of accumulating new residue and undergoing
to plowing the residue in right away,” he says, noting
decomposition by soil fauna.
that as a result “there will be less kick-up of sod bunnies
“As a society, we’ve made much too big a footprint
into my [mechanical] bean picker.”
on the land,” Kenagy once told the Oregon Statesman
Kenagy’s commitment to building good soil goes
Journal. “I think it’s time to make it smaller.”
beyond planting cover crops. Whenever possible, he uses
—uPdated by aMy kreMen
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building soils For better CroPs: sustainable soil ManageMent
