|
INTRODUCTION TO CHARTS
The four comprehensive charts that follow can help orient you to
the major cover crops most appropriate to your needs and region.
Bear in mind that choice of cultivar, weather extremes and other
factors may affect a cover crop’s performance in a given year.
CHART 1: TOP REGIONAL COVER CROP SPECIES
This chart lists up to five cover crop recommendations per broad
bioregion for six different major purposes: N Source, Soil Builder,
Erosion Fighter, Subsoil Loosener, weed Fighter and Pest Fighter.
If you know your main goal for a cover crop, Chart 1 can suggest
which cover crop entries to examine in the charts that follow and
help you determine which major cover narrative( s) to read first.
Disclaimer. The crops recommended here will not
be the most successful in all cases within a bioregion, and others
may work better in some locations and in some years. The listed
cover crops are, however, thought by reviewers to have the best
chance of success in most years under current management regimes.
CHART 2: PERFORMANCE AND ROLES
This chart provides relative ratings (with the exception of two
columns having quantitative ranges) of what the top covers do best,
such as supply or scavenge nitrogen, build soil or fight erosion.
Seasonality has a bearing on some of these ratings. A cover that
grows best in spring could suppress weeds better than in fall. Unless
otherwise footnoted, however, the chart would rate a cover’s
performance (relative to the other covers) for the entire time period
it is likely to be in the field. Ratings are general for the species,
based on measured results and observations over a range of conditions.
The individual narratives provide more seasonal details. The added
effect of a nurse crop is included in the “Weed Fighter”
ratings for legumes usually planted with a grain or grass nurse
crop.
Column headings
Legume N Source. Rates legume cover crops for their relative
ability to supply fixed N. (Nonlegumes have not been rated
for their biomass nitrogen content, so this column is left blank
for nonlegumes.)
Total N. A quantitative estimate of the
reasonably expected range of total N provided by a legume stand
(from all biomass, above and below ground) in lb. N/A, based mostly
on published research. This is total N, not the fertilizer replacement
value. Grasses have not been rated for their biomass nitrogen
content because mature grass residues tend to immobilize N. Brassicas
are less likely to immobilize N than grasses.
Dry Matter. A quantitative estimate of
the range of dry matter in lb./A /yr., based largely on published
research. As some of this data is based on research plots, irrigated
systems or multicut systems, your on-farm result probably would
be in the low to midpoint of the dry matter range cited. This estimate
is based on fully dry material. “Dry” alfalfa hay is
often about 20 percent moisture, so a ton of hay would only be 1,600
lb. of “dry matter.”
N Scavenger. Rates a cover crop’s ability
to take up and store excess nitrogen. Bear in mind that the sooner
you plant a cover after main crop harvest— or overseed a cover
into the standing crop—the more N it will be able to absorb.
Soil Builder. Rates a cover crop’s ability
to produce organic matter and improve soil structure. The ratings
assume that you plan to use cover crops regularly in your cropping
system to provide ongoing additions to soil organic matter.
Erosion Fighter. Rates how extensive and how quickly
a root system develops, how well it holds soil against sheet and
wind erosion and the influence the growth habit may have on fighting
wind erosion.
Weed Fighter. Rates how well the cover crop outcompetes
weeds by any means through its life cycle, including killed residue.
Note that ratings for the legumes assume they are established with
a small-grain nurse crop.
Good Grazing. Rates relative production, nutritional
quality and palatability of the cover as a forage.
Quick Growth. Rates the speed of establishment
and growth.
Lasting Residue. Rates the effectiveness of the
cover crop in providing a long-lasting mulch.
Duration. Rates how well the stand can provide
long-season growth.
Harvest Value. Rates the cover crop’s economic
value as a forage (F) or as a seed or grain crop (S), bearing in
mind the relative market value and probable yields.
Cash Crop Interseed. Rates whether the cover crop
would hinder or help while serving as a companion crop.
CHART 3A : CULTURAL TRAITS
This chart shows a cover crop’s characteristics such as life
cycle, drought tolerance, preferred soils and growth habits. The
ratings are general for the species, based on measured results and
observations over a range of conditions. Choice of cultivar, weather
extremes and other factors may affect a cover crop’s performance
in a given year.
Column headings
Aliases. Provides a few common names for the cover crop.
Type. Describes the general life cycle of the
crop.
B = Biennial. Grows vegetatively during its first
year and, if it successfully overwinters, sets seed during its second
year.
CSA = Cool-Season Annual. Prefers cool temperatures
and depending on which Hardiness Zone it is grown in, could serve
as a fall, winter or spring cover crop.
SA = Summer Annual. Germinates and matures without
a cold snap and usually tolerates warm temperatures.
WA = Winter Annual. Cold-tolerant, usually planted
in fall and often requires freezing temperatures or a cold period
to set seed.
LP = Long-lived Perennial. Can endure for many
growing seasons.
SP = Short-lived Perennial. Usually does not persist
more than a few years, if that long.
Hardy Through Zone. Refers to the standard USDA
Hardiness Zones. See map on inside front cover. Bear in mind that
regional microclimate, weather variations, and other near-term management
factors such as planting date and companion species can influence
plant performance expectations.
Tolerances. How well a crop is likely to endure
despite stress from heat, drought, shade, flooding or low fertility.
The best rating would mean that the crop is expected to be fully
tolerant.
Habit. How plants develop.
C = Climbing
U = Upright
P = Prostrate
SP = Semi-Prostrate
SU = Semi-Upright
pH Preferred. The pH range in which a species
can be expected to perform reasonably well.
Best Established. The season in which a cover
crop is best suited for planting and early growth. Note that this
can vary by region and that it’s important to ascertain local
planting date recommendations for specific cover crops. Season:
F = Fall ; Sp = Spring; Su = Summer; W =Winter Time: E = Early;
L = Late; M = Mid
Minimum Germination Temperature. The minimum soil
temperature (F) generally required for successful germination and
establishment.
CHART 3B: PLANTING
Depth. The recommended range of seeding depth
(in inches), to avoid either overexposure or burying too deeply.
Rate. Recommended seeding rate for drilling and
broadcasting a pure stand in lb./A, bu/A. and oz./100 sq. ft., assuming
legal standards for germination percentage. Seeding rate will depend
on the cover crop’s primary purpose and other factors. See
the narratives for more detail about establishing a given cover
crop. Pre-inoculated (“rhizo-coated”) legume seed weighs
about one third more than raw seed. Increase seeding rate by one-third
to plant the same amount of seed per area.
Cost. Material costs (seed cost only) in dollars
per pound, based usually on a 50-lb. bag as of fall 2006. Individual
species vary markedly with supply and demand. Always confirm seed
price and availability before ordering, and before planning to use
less common seed types.
Cost/A. Seed cost per acre based on the midpoint
between the high and low of reported seed prices as of fall 1997
and the midpoint recommended seeding rate for drilling and broadcasting.
Your cost will depend on actual seed cost and seeding rate. Estimate
excludes associated costs such as labor, fuel and equipment.
Inoculant Type. The recommended inoculant for
each legume. Your seed supplier may only carry one or two common
inoculants. You may need to order inoculant in advance. See Seed
Suppliers.
Reseeds. Rates the likelihood of a cover crop
reestablishing through self-reseeding if it’s allowed to mature
and set seed. Aggressive tillage will bury seed and reduce germination.
Ratings assume the tillage system has minimal effect on reseeding.
Dependable reseeding ability is valued in some orchard, dryland
grain and cotton systems, but can cause weed problems in other systems.
See the narratives for more detail.
CHARTS 4A AND 4B
These charts provide relative ratings of other management considerations—benefits
and possible drawbacks—that could affect your selection of
cover crop species.
The till-kill rating assumes tillage at an appropriate stage. The
mow-kill ratings assume mowing at flowering, but before seedheads
start maturing. See sectional narratives for details.
Ratings are based largely on a combination of published research
and observations of farmers who have grown specific covers. Your
experience with a given cover could be influenced by site-specific
factors, such as your soil condition, crop rotation, proximity to
other farms, weather extremes, etc.
CHART 4A : POTENTIAL ADVANTAGES
Soil Impact. Assesses a cover’s relative
ability to loosen subsoil, make soil P and K more readily available
to crops, or improve topsoil.
Soil Ecology. Rates a cover’s ability to
fight pests by suppressing or limiting damage from nematodes, soil
disease from fungal or bacterial infection, or weeds by natural
herbicidal (allelopathic) or competition/smothering action. Researchers
report difficulty in conclusively documenting allelopathic activity
distinct from other cover crop effects, and nematicidal impacts
are variable, studies show. These are general, tentative ratings
in these emerging aspects of cover crop influence.
Other. Indicates likelihood of attracting beneficial
insects, of accommodating field traffic (foot or vehicle) and of
fitting growing windows or short duration.
CHART 4B: POTENTIAL DISADVANTAGES
Increase Pest Risks. Relative likelihood of a
cover crop becoming a weed, or contributing to a likely pest risk.
Overall, growing a cover crop rarely causes pest problems, but certain
cover crops may contribute to particular pest, disease or nematode
problems in localized areas, for example by serving as an alternate
host to the pest. See the narratives for more detail.
Readers note the shift in meaning for symbols on this chart only.
Management Challenges. Relative ease or difficulty
of establishing, killing or incorporating a stand. “Till-kill”
refers to killing by plowing, disking or other tillage. “Mature
incorporation” rates the difficulty of incorporating a relatively
mature stand. Incorporation will be easier when a stand is killed
before maturity or after some time elapses between killing and incorporating.
Top | Nonlegume
Overview
|
