Vol. 17, No. 3, 1996
Seeding Cover Crops in Kentucky
K.L. Wells and M.J. Bitzer
The most common reason for seeding a cover crop is to establish cover onto a tilled
area following harvest of the previous crop, or onto a disturbed area for a "critical
seeding", as soon as possible after tillage or disturbance. The reason for establishing
the cover crop is to stabilize the exposed surface of bare soil to prevent erosion.
The need for cover crops most commonly occurs after a crop is harvested in a
system where the field is not likely to be cropped again for several weeks or months
after crop harvest. This commonly occurs in Kentucky following harvest
of tobacco or other summer grown crops on fields which lay idle during the late summer,
fall, and winter until the following spring when they will be prepared for the next
sequence of crops. "Critical seeding" areas such as waterways, stream bank
stabilization, terraces, diversion ditches, and other such areas which are mechanically
re-formed are also areas on which cover crops are commonly sown
in order to stabilize the soil surface until permanent vegetation can be established.
Establishment of cover crops on such areas for this purpose is a recommended best
management practice of proven value for erosion control.
Dates For Seeding Cover Crops
There is no absolute date or range of dates for seeding cover crops. This is
because the date of seeding should be determined by date of the previous crop
removal or when an area is tilled or disturbed for a "critical seeding". There
is a wide range of time in which tillage or disturbance may be done, depending
on the specific situation involved and existing climatic conditions. The critical
objective for seeding a cover crop is to establish a vegetative cover as
soon as possible after tillage or disturbance. While sowing a cover crop
following tobacco harvest may not occur until mid-August or later, sowing
cover crops onto "critical seeding" areas may be done whenever mechanical
preparation of the site is completed. Generally, this may occur from
March through November.
The seeding of winter small grains (wheat, barley, rye, oats, and triticale) to
be harvested as grain, silage, hay, or grazing is a cropping practice which
serves a dual purpose. While the intent for such seedings is to produce a
crop for harvest, it also provides soil protection against erosion during the fall,
winter, and early spring months, between the harvest of one summer annual crop until
establishment of the next summer annual crop. If the primary purpose of seeding
wheat is for producing a grain crop, seeding is not recommended until after threat of
Hessian fly infestation has passed. This would normally occur around the middle of
October in Kentucky.
Species Used for Seeding Cover Crops
Since the objective for seeding a cover crop is to re-establish vegetative cover
as rapidly as possible, species whose seeds rapidly germinate serve the best.
For this reason, small grains, especially wheat and rye, are often used since
with adequate soil moisture, they will germinate and seedling growth will be
initiated within 7 days at soil temperatures around 65oF. Germination takes longer
as soiltemperature becomes cooler, being about 14 days at a soil temperature of 50 F.
Methods of Seeding Cover Crops
The agronomic principle involved in seedings is to establish seed-soil contact
so that enough soil moisture can be absorbed by the seed from the soil to initiate
germination. Methods range from simply broadcasting the seeds over the disked
field or area by hand or by use of a hand-powered or mechanically powered
cyclone seeder, or by mechanical drills specially designed to place seeds in rows
at a precise depth and to firm the soil around the seeded row. The degree of
seed-soil contact obtained by the seeding method used is important in
establishing a cover thick enough to provide erosion control. The most risky
practice is to broadcast seeds on top of the soil with no further tillage to
incorporate them into the soil. The risk for poor stands in this situation can
be lowered somewhat by increasing seeding rates by about 50% that normally
used if seeds are incorporated into the soil. A light disking of the soil surface
following broadcast seedings is commonly used to provide for better seed-soil
contact and to require less seed. Use of mechanical drills to place seeds in rows
at a proper depth in soil is the least risky method of establishing a
satisfactory vegetative cover.
Seeding Rates For Small Grain Species
The following table shows recommended seeding rates and
resultant seeds per square foot or foot of drill row.
Table 1. Seeding Rates and Densities for Small Grains(1)
_________________________________________________________________
seeding rates
recommended Forage Seeding Density(4)
(bu/a)(3) ________________________
_____________ broadcast 7" drilled rows
Species lbs/bu seeds/lb(2) forage grain (seeds/ft) (seeds/ft of row)
_______________________________________________________________________________
wheat 60 14,500 2-2.5 1-1.5 36-44 21-26
rye 56 18,000 2-3 1-1.5 41-62 24-39
barley 48 13,000 2.5-3 1.5-2 32-38 19-22
oats 32 14,000 2.5-3 2-3 23-28 14-16
triticale 50 11,000 1.5-2 -- 17-23 10-13
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1/ Grain and Forage Crop Guuide for Kentucky. UK Coop. Ext. Serv. Publ.
AGR-18 (rev March 1995).
2/ number/lb may vary as seed size varies.
3/ for cover crop seedings where seed will be incorporated into soil, use the forage
seeding rate. If seeds are not incorporated into soil, increase seeding rates by 50%.
4/ based on forage seeding rates and 90% germination.
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