Practical Farmers of Iowa
Cooperators
Bill Buman, Harlan; Devan Green,
Conrad; Jim Funcke, Jefferson;
Randy Caviness, Greenfield; Rick
Juchems, Plainfield; and Larry
Ness, Whiterock Conservancy, Coon
Rapids
Project Timeline
Initiated Fall 2008 and projected for
5 years
Web Link
practicalfarmers.org/resources
Contact
Sarah Carlson (515)232-5661,
[email protected]
Funding
Iowa Dept. of Agriculture and Land
Stewardship (IDALS) in partnership
with the Iowa Learning Farms,
Walton Family Foundation
Background
Cover crops provide multiple benefits to the
farming system. Incorporating more “green”
plants into the “brown” months will help to
protect water quality and maintain natural
cycles for water, carbon, nutrients, and soil
organisms.
Although cover crops are an excellent practice
for farmers to incorporate, few currently use
cover crops. Iowa farmers planted cover crops
on approximately 17,000A of the 23 million
corn and soybean acres in the state in 2008.
Farmers have not adopted cover crops as a
part of their farming system on a broad scale
due to timing constraints in the fall following
harvest and concerns about cover crop’s
potential negative effect on the following
year’s crop yield. Research on cover crops’
effect from PFI cooperators’ projects since
1987 and from the National Laboratory for
Agriculture and the Environment (NLAE,
formerly Tilth Lab) has been mixed. But in
most of these studies, the cover crop was
not planted in the same field every year.
PFI farmers have observed that cover crops
improve their soil’s productive capacity.
Could cover crops planted in the same field
for more than five years show differing effects
Tel: (515) 232-5661
Fax: (515) 232-5649
www.practicalfarmers.org
Cover Crops’ Effect on Cash Crop
Yield
Abstract
Cover crops are an important tool farmers may use to retain nitrogen and soil on
their farm fields. However, many farmers are concerned about the negative effects of
this cultural practice on their cash grain yields. After year one of this 5-year study,
a winter cover crop only negatively affected cash crop yield at one location. Poor
control of the cover crop by the herbicide Liberty caused a decreased yield in corn
grain at one location. At three of the six locations, cover crop biomass measured
more than 500lbs/A. An earlier fall planting date and later spring termination date
increased the growing degree days available to establish the cover crop.
on the yield of the following cash crop?
Several studies have been conducted but few
have involved planting the cover crop in the
same location in consecutive years. This fiveyear study will measure the yield of corn and
soybeans in cover and no cover treatments
to determine if the cover crop has a negative
effect on the cash grain yield.
Method
To study this question, six sites were
established in the fall of 2008. These sites were
located at Harlan (SW), Greenfield (SW),
Coon Rapids (West Central), Jefferson (West
Central), Plainfield (NE) and Conrad (East
Central). Table 1 explains the previous and
following cash crop in each farming system.
All sites planted a winter hardy rye cover
crop. Some rye was sourced through local
seed retailers and others planted ‘wheeler,’
an improved variety bred at Michigan State
University. Farmers planted cover and no
cover treatments in the fall following cash
grain or corn silage harvest. In the spring
some farmers tilled in the cover crop or used
an herbicide to terminate it before planting
corn or soybeans. In the spring before the
cover crop was killed, samples of the aboveground biomass were collected, dried, and
weighed. The concentration of nitrogen in
the biomass was also measured to determine
how much nitrogen the cover crop held
in the farming system. In the fall, farmers
combined and weighed grain from individual
plots using a weigh wagon or a yield monitor.
Corn yields are reported at 15.5% moisture
content. Soybean yields are reported at 13%
moisture content.
Results
Corn was planted in the spring of 2009
following a rye cover crop at four locations
(Jefferson, Conrad, Harlan, Greenfield).
At three of those locations, no statistically
significant difference was measured between
corn yield in the cover treatment or the no
cover treatment. At Jefferson, corn yielded 39
bu/A, less in the cover treatment as compared
Table 1. Description of farming system at each location in Iowa.
Fall Crop
Spring Crop
*Conrad (East Central)
Small Grain
Corn
Plainfield (NE)
Corn Silage
Soybean
Coon Rapids (West Central)
Soybean
Corn
Harlan (SW)
Soybean
Corn
Greenfield (SW)
Soybean
Corn
Jefferson (West Central)
Soybean
Corn
*Conrad is a certified organic farm. A cover crop will be used each year
but it will vary and the rotation will include a greater diversity of crops
compared to the other locations.
137 Lynn Avenue, Suite 200
Ames, Iowa 50014
Email: [email protected]
Web: www.practicalfarmers.org
Practical Farmers of Iowa
www.practicalfarmers.org
to the no cover treatment (Table 1 and Fig. 1). The farmer cooperator
used Liberty brand herbicide to terminate the cover crop in the spring
and had extremely poor control. The cover crop (see photo) was over
half the height of the corn and competed aggressively with the cash
crop. The failure of the Liberty brand herbicide was determined to be
a function of wet weather.
Cooperator Larry Ness at Whiterock Conservancy
Soybeans were planted in the spring of 2009 at two locations. No
difference between soybean yield on the cover and no cover treatments
existed (Fig. 2).
bu/A
Cover crop biomass was also harvested in the spring to see if the
amount of biomass would influence the crop yield negatively.
Poor chemical control of rye cover crop; decreased
However, biomass was sampled when farmers predicted that they
corn yields as a result
would terminate the cover crop and plant within one or two days.
In reality, cover crop biomass was harvested one to two
weeks prior to termination and planting. After the biomass
Table 2. Corn yield in bu/A at 15.5% at four locations in Iowa
was harvested, dried and weighed, the total carbon and total
planted with and without cover crops
nitrogen were measured. Figure 3 shows the biomass harvested
Treatment Harlan, IA
Greenfield, IA Conrad, IA Jefferson, IA*
from each farming system in lbs/A. Figure 4 shows the amount
Cover
209
203
91
155
of nitrogen in lbs/A that was held by that biomass in each
No Cover
204
195
91
194
farming system. The farming systems with the earlier fall
planting date and late spring kill date grew more biomass.
Research from the NLAE measures cover crop benefit
2009 Corn Yield
to the soil when more than 500lbs/A biomass is present.
250
Three of the farming systems, cc following small grain
before corn, cc after corn silage before soybean and cc
200
after soybean before corn achieved this level of biomass.
*
150
Conclusions
100
50
0
Harlan, IA
Greenfield, IA
Cover
Conrad, IA
Jefferson, IA
No Cover
Figure 1. 2009 Corn yield in bu/A at 15.5% harvested from plots planted with
and without a rye cover crop.
After year one of this 5-year study, a winter cover crop
only negatively affected cash crop yield at one location.
Poor control of the cover crop by the herbicide Liberty
caused a decreased yield in corn grain at one location. At
three of the six locations, cover crop biomass measured
more than 500lbs/A. An earlier fall planting date and later
spring termination date increased the growing degree days
available to establish the cover crop.
2009 Soybean Yield
70
60
bu/A
50
40
30
20
10
0
Plainfield, IA
Coon Rapids, IA
Cover
No Cover
Figure 2. 2009 Soybean yield in bu/A at 13% harvested from plots planted with
and without a rye cover crop.
Tel: (515) 232-5661
Fax: (515) 232-5649
137 Lynn Avenue, Suite 200
Ames, Iowa 50014
Report prepared February 2010
Email: [email protected]
Web: www.practicalfarmers.org
Practical Farmers of Iowa
www.practicalfarmers.org
1200
1000
lbs/A
800
600
400
200
0
Conrad
Plainfield
Coon Rapids
Harlan
Greenfield
Jefferson
9/24/08
9/15/08
10/30/08
10/1/08
10/30/08
11/3/08
5/18/09
4/17/09
5/8/09
4/22/09
4/22/09
4/28/09
Figure 3. Aboveground biomass (lbs/A) of rye harvested in the spring at each farm site.
30
25
N-lbs/A
20
15
10
5
0
Conrad
Plainfield
Coon Rapids
Harlan
Greenfield
Jefferson
9/24/08
9/15/08
10/30/08
10/1/08
10/30/08
11/3/08
5/18/09
4/17/09
5/8/09
4/22/09
4/22/09
4/28/09
Figure 4. Amount of nitrogen (N-lbs/A) held in the above-ground biomass of a rye cover crop at
each farm site.
Tel: (515) 232-5661
Fax: (515) 232-5649
137 Lynn Avenue, Suite 200
Ames, Iowa 50014
Email: [email protected]
Web: www.practicalfarmers.org