Content uploaded by D.C. Nielsen
Author content
All content in this area was uploaded by D.C. Nielsen on Aug 26, 2015
Content may be subject to copyright.
Agronomy Journal • Volume 107, Issue 6 • 2015 2047
U in cropping systems is promoted
based on several benecial consequences that follow
their use, including reduced erosion, increased soil
organic matter, increased inltration rates and precipitation
storage, increased nutrient availability, reduced nutrient loss,
and weed suppression (Snapp et al., 2005; Petrosino et al.,
2015). Both wind and water erosion are sources of concern
for dryland production systems in the Central Great Plains
(Skidmore and Siddoway, 1978; Skidmore et al., 1979; Blanco-
Canqui et al., 2013). Replacing fallow in a winter wheat–fallow
system in southwestern Kansas with a variety of single-species
or legume–triticale cover crop mixtures was found to reduce
the soil’s susceptibility to wind erosion and to reduce runo
loss of sediment, total P, and NO3–N (Blanco-Canqui et al.,
2013). However, this study also reported that these benets of
cover crops diminished rapidly with time aer cover crop ter-
mination. In that study cover crops had been part of the crop-
ping system for 5 yr, but aer only 9 mo of no longer including
cover crops in the system there were no discernible eects on
the measured soil properties.
e historical, conventional denition of cover crops
stated that the crop is not taken for a protable purpose
(Lal et al., 1991). However, more recent denitions of cover
cropping allow for the use of the cover crop for animal feed
(Franzluebbers and Stuedemann, 2008) so that there can be
some direct protability from growing the cover crop. For such
protability to occur there must be enough biomass produced
by the cover crop such that a portion can be grazed or taken
for forage while maintaining enough residual mass and surface
cover to prevent soil erosion. Under the water-limited condi-
tions of the semiarid Central Great Plains, producing enough
Crop Economics, Production & Management
Cover Crop Biomass Production and Water Use
in the Central Great Plains
David C. Nielsen,* Drew J. Lyon, Gary W. Hergert, Robert K. Higgins, and Johnathan D. Holman
Published in Agron. J. 107:2047–2058 (2 015)
doi:10.2134/agronj15.0186
Received 16 Apr. 2015
Accepted 6 July 2015
Copyright © 2015 by the American Society of Agronomy
5585 Guilford Road, Madison, WI 53711 USA
All rights reserved
ABSTRACT
e water-limited environment of the semiarid Central Great
Plains may not produce enough cover crop biomass to generate
benets associated with cover crop use in more humid regions.
ere have been reports that cover crops grown in mixtures
produce more biomass with greater water use eciency than
single-species plantings. is study was conducted to determine
dierences in cover crop biomass production, water use e-
ciency, and residue cover between a mixture and single-species
plantings. e study was conducted at Akron, CO, and Sidney,
NE, during the 2012 and 2013 growing seasons under both
rainfed and irrigated conditions. Water use, biomass, and resi-
due cover were measured and water use eciency was calculated
for four single-species cover crops (ax [Linum usitatissimum
L.], oat [Avena sativa L.], pea [Pisum sativum ssp. arvense L.
Poir], rapeseed [Brassica napus L.]) and a 10-species mixture.
e mixt ure did not produce greater biomass nor exhibit greater
water use eciency than the single-species plantings. e slope
of the water-limited yield relationship was not signicantly
greater for the mixture than for single-species plantings. Water-
limited yield relationship slopes were in the order of rapeseed <
ax < pea < mixture < oat, which was the expected order based
on previously published biomass productivity values generated
from values of glucose conversion into carbohydrates, protein,
or lipids. Residue cover was not generally greater from the mix-
ture than from single-species plantings. e greater expense
associated with a mixture is not justied unless a certain cover
crop forage quality is required for grazing or haying.
D.C. Nielsen, USDA-ARS, Central Great Plains Research Station,
40335 County Rd. GG, Akron, CO 80720; D.J. Lyon, Dep. Crop
and Soil Sciences, Washington State Univ., 169 Johnson Hall, P.O.
Box 646420, Pullman, WA 99164-6420; G.W. Hergert, Univ. of
Nebraska Panhandle Research and Extension Center, 4502 Ave. I,
Scottsblu, NE 69361; and R.K. Higgins, Univ. of Nebraska, High
Plains Ag. Lab., 3257 Rd 109, Sidney, NE 69162; J.D. Holman,
Southwest Research and Extension Center, 4500 East Mary St.,
Garden City, KS 67846. Disclaimer: e use of trade, rm, or
corporation names is for the information and convenience of the
reader. Such use does not constitute an ocial endorsement or
approval by the U.S. Department of Agriculture (USDA) or the
Agricultural Research Service of any product or service to the
exclusion of others that may be suitable. e USDA prohibits
discrimination in all its programs and activities on the basis of
race, color, national origin, age, disability, and where applicable,
sex, marital status, familial status, parental status, relig ion, sexual
orientation, genetic information, politica l beliefs, reprisal, or because
all or part of an individual ’s income is derived f rom any public assistance
program . *Corresponding author (david.n ielsen@ars.us da.gov).
Published August 21, 2015
2048 Agronomy Journal • Volume 107, Issue 6 • 2015
biomass from cover crops to suciently meet both of these
needs (i.e., wind erosion control and protable forage produc-
tion) may be a challenge.
Some reports of cover crop biomass production from the
Northern Great Plains (Aase and Pikul, 2000; Carr et al.,
2004; Chen et al., 2004, Miller et al., 2006) would suggest that
cover crop production is sucient to produce both protable
forage production and wind erosion protection. But Briggs
and Shantz (1917) provided data that demonstrated that the
amount of water required to produce a unit of plant biomass
increased signicantly as one moved from north to south
across the Great Plains of the United States. For example, they
reported 518 g of water to produce a gram of alfalfa (Medicago
sativa L.) in Williston, ND, and 1005 g of water to produce a
gram of alfalfa in Dalhart, TX. is dierence is due to the
evaporative demand dierences that exist across the region
as quantied by the strong north to south gradient of pan
evaporation across the Great Plains (Tanner and Sinclair,
1983; Robinson and Nielsen, 2015; Farnsworth et al., 1982;
Stewart and Peterson, 2014; Sinclair and Weiss, 2010). Tanner
and Sinclair (1983) indicated that dry matter production was
inversely related to pan evaporation. at observation is sup-
ported by comparing the water use eciency data that can
be extracted from Nielsen (2001) in the Central Great Plains
and Miller et al. (2002) in the Northern Great Plains for pea,
chickpea (Cicer arietinum L.), and lentil (Lens culinaris L.)
(Table 1). For all three crops, water use eciencies were greater
in the Northern Great Plains (lesser pan evaporation) than in
the Central Great Plains (greater pan evaporation). Likewise
Robinson and Nielsen (2015) showed increasing intercepts
and decreasing slopes of water use/yield production functions
(indicating decreasing water use eciency) of wheat (Triticum
aestivum L.) and corn (Zea mays L.) as location changed from
Northern to Southern Great Plains with concomitant increas-
ing pan evaporation (relationships from Brown, 1971; Nielsen
et al., 2011; C. Robinson, personal communication, 15 Dec.
2014). erefore, transferring cover crop production results
from the nNorthern Great Plains to the higher evaporative
demand environment of the Central and Southern Great Plains
should be done with some caution.
Treadwell et al. (2010) stated that cover crop species mix-
tures are planted to optimize C/N balance, obtain multiple
benets, or more fully achieve a particular objective such as
organic matter production or weed suppression. ey also
stated that planting a mixture of cover crops can reduce risk
of crop failure, although dealing with mixtures can require
additional planning and labor. In addition, they noted that
mixtures can be used to enhance alleopathic eects to control
weeds and to either attract benecia l insects or deter pest insects.
However, they did not provide any information relative to increased
biomass production by mixtures compa red with monocultures.
Others have observed that mixtures of species can produce
more biomass than monocultures. Tilman et al. (2001) pre-
sented data from east-central Minnesota documenting the
observation that mixtures of perennial grasses, legumes, non-
legume forbes, and woody species produced greater amounts
of aboveground biomass as number of species in the mixtures
increased from 1 to 16 species. Cardinale et al. (2007) analyzed
data from 44 independent experiments from temperate grass-
lands, tundra, estuaries, or temperate bryophyte assemblages
and concluded that species mixtures produced an average of 1.7
times more biomass than monocultures.
Clark (2012) stated that cover crop mixtures will improve
biomass production compared with single species, and spe-
cically that oat can improve the productivity of legumes
when planted in mixtures, although no data were presented.
Published studies with annual cover crop species have shown
mixed results. Robinson (1960) presented data from a south-
ern Minnesota study that showed greater forage yield for an
oat–pea mixture compared with oat alone on a sandy soil,
but not on a silt loam or clay loam soil. In that same study
there was no yield advantage for an oat–vetch (Vicia sativa L.)
mixture compared with oat alone. Dunavin (1987) found in
a Florida study that two- and three-species mixtures of tur-
nip–Chinese cabbage hybrid [Brassica campestris var. rapa L.
X B. pekinensis (Lour.) Rupr.], rape (B. napus L.), rye (Secale
cereale L.), ryegrass (Lolium multiorum Lam.), and crimson
clover (Trifolium incarnatum L.) produced more dry matter
than all of the separate species grown as monocultures, except
ryegrass (ryegrass was a component of all of the mixtures).
LaChance and Bradley (2014) reported on 2 yr of biomass data
collected in central Pennsylvania with cover crop monocultures
and mixtures (three-, four-, six-, and seven-species mixtures)
planted following winter wheat harvest. e fall growth of the
mixtures was generally greater than that of the single-species
plantings of rye, canola (B. napus L.), radish (Raphanus sati-
vus L.), and red clover (T. pratens e L.), but not of pea and oat.
Carr et al. (2004) found the dry matter yields of oat–pea and
barley (Hordeum vulgare L.)–pea mixtures were greater than
single-species plantings of oat and barley when planted in a
low-soil-N environment in southwestern North Dakota. In
that same study the dry matter production of pea was greater
than oat–pea and barley–pea in the low-N environment. Carr
et al. (1998) reported that dry matter yield was not increased
and may be reduced when pea was intercropped with cereals
under high-soil-N conditions. Lenssen et al. (2010) evaluated
5 yr of forage production in northeastern Montana and found
the dry matter yields of barley and a barley–pea mixture to
be equal in each year. Working in the semiarid environment
of Cyprus, Droushiotis (1989) found that average dry matter
yields of single-species plantings of oat and triticale were the
same as mixtures of those species with pea, and that total dry
Table 1. Water use efciency (kg ha–1 mm–1) of seed production for pea, chickpea, and lentil in the Central Great Plains (Nielsen, 2001)
and Northern Great Plains (Miller et al., 2002).
Species
Central Great Plains Northern Great Plains
Average Range (No. of observations) Average Range (No. of observations)
Pea 7.3 3.9–11.1 (32) 8.5 4.1–16.3 (29)
Chickpea 5.3 2.7–8.2 (36) 6.2 2.5–13.6 (24)
Lentil 3.0 1.8–4.5 (31) 4.8 0.5–11.7 (30)
Agronomy Journal • Volume 107, Issue 6 • 2015 2049
matter production decreased linearly as the seed proportion of
the legume component in the mixture increased.
Brown (2011) presented some unreplicated, on-farm data
collected from central North Dakota documenting nearly three
times greater dry matter production (5115 vs. 1770 kg ha–1) for
cover crops grown in a six-species mixture compared with mono-
cultures grown during 1 yr (2006) on 38 mm of growing season
precipitation (Table 2). Dierences were attributed to dierences in
rooting depth (no measurements were made to conrm this hypoth-
esis) and how the soil functions with a diversity of plant species
present (unspecied functioning mechanism).
Several factors can aect the relationship between dry mat-
ter production and crop water use, including photosynthetic
eciency (e.g., C3 vs. C4 carboxylation pathway; Kramer,
1983), energy requirements to produce dierent plant com-
positions (e.g., starch, protein, oil; Tanner and Sinclair, 1983),
timing of precipitation and level of water stress at particular
phenological stages of development (Nielsen et al., 2009), pest
(weed, insect, disease) problems, shattering losses, limited soil
fertility, soil physical limitations, hail, frost, limited plant pop-
ulations, etc. (Angus and van Herwaarden, 2001; Passioura and
Angus, 2010). French and Schultz (1984) demonstrated the
usefulness of plotting dry matter or seed yield against growing
season water use and then tting a “frontier” line to the plotted
data that dened the water-limited yield. e slope of this line
quantied the target water use eciency that farmers should be
trying to attain through proper management. is data analysis
method provides an opportunity to assess whether water use e-
ciency of cover crop dry matter production of mixtures is dierent
from dry matter production for single-species plantings.
We have not been able to nd data comparing productiv-
ity of cover crop species grown in mixtures vs. single-species
plantings under the semiarid climate conditions of the Central
Great Plains that would support the nding of enhanced pro-
ductivity of mixtures compared with single species plantings
reported by Tilman et al. (2001) using perennial species or
Brown (2011) using annual species. erefore, the objectives of this
study were to (i) determine whether a 10-species cover crop mixture
produced more biomass than single-species plantings; (ii) determine
whether a 10-species cover crop mixture ex hibited greater water
use eciency of dr y matter production than sing le-species plant-
ings; and (iii) quantify residue cover dierences on the soil surface
between a 10-species cover crop mixture and single-species plantings
at cover crop termination and subsequent winter wheat planting.
MATERIALS AND METHODS
e study was conducted during the 2012 and 2013 grow-
ing seasons at the USDA-ARS Central Great Plains Research
Station, 6.4 km east of Akron, CO, (40°09¢ N, 103° 09¢ W,
1384 m elevation above sea level) and at the University of
Nebraska High Plains Ag Lab, 9.7 km northwest of Sidney,
NE , (41°12¢ N, 103°0¢ W, 1315 m elevation above sea level).
e soil type at both locations was silt loam (Akron: Weld silt
loam (ne, smectitic, mesic Aridic Argiustoll); Sidney: Keith silt
loam (ne-silty, mixed, superactive, mesic Aridic Argiustoll).
e cropping system being investigated was a no-till proso
millet (Panicum miliaceum L.)–spring cover crop–winter
wheat rotation. In this system proso millet was harvested in
mid-September and a cover crop was planted in early April.
e cover crop was terminated in mid-June and winter wheat
was planted in late September. e experiment was laid out as
a split plot design with four replications at both locations. e
main plot factor was irrigation treatment (rainfed or irrigated)
and the split plot factor was cover crop species (four single-
species cover crop plantings [ax, oat, pea, rapeseed] and one
10-species cover crop mixture). Additionally, a no-till fallow
treatment (no crop between millet harvest and wheat planting)
was included to evaluate changes in soil surface residue cover
that occurred over time. Main plots were 6.1 by 54.6 m (2012)
and 12.2 by 36.6 m (2013) at Akron and 4.6 by 54.6 m (both
years) at Sidney. Individual split plot dimensions were 6.1 by
9.1 m (2012) and 6.1 by 12.2 m (2013) at Akron, and 4.6 by
9.1 m (both years) at Sidney. Planting dates, seeding rates, and
mixture composition are given in Table 3. Seeding rates were
recommended by Green Cover Seed, Bladen, NE . Planting date at
Sidney in 2013 was delayed until 30 Apri l because of wet conditions.
At both Akron and Sidney all cover crop treatments were
no-till seeded into proso millet residue le following proso mil-
let harvest the previous September. Row spacing was 0.20 m at
Akron and 0.25 m at Sidney. e plot area was sprayed with glypho-
sate [N-(phosphonomethyl)glycine] before planting and fertilized
with 34 kg N ha–1 (32–0–0) at Akron so that there would be no
N-fertility limitations to cover crop growth and water use eciency
of biomass production could be accurately assessed. Soil testing at
Sidney determined that no fertilizer was required. Hand-weeding
was performed periodically at A kron and Sidney during the growing
season, with most of that performed during the last week of April.
At Akron the irrigated plots were irrigated bi-weekly to
simulate average precipitation at Blue Hill, NE, (south-central
Nebraska, near the site of the study by Berns and Berns (2009))
to determine if cover crop water use/yield dierences or
similarities between single-species plantings and the mixture
remained the same in a higher rainfall regime but with similar
evaporative demand (about 1830 mm per year; Kohler et al.,
1959). e irrigated plots at Sidney were irrigated bi-weekly to
simulate the 30-yr average precipitation at Sidney. Because of
the severe drought conditions experienced at Akron in 2012,
the dryland plots received enough supplemental irrigation
to keep them at 80% of the long-term average precipitation
received at Akron. Observed and average monthly precipitation
and irrigation amounts are shown in Table 4. Irrigations at both
locations were applied through linear move irrigation systems,
and 13 to 19 mm of water was applied with each irrigation.
Table 2. Dry matter production of cover crops grown as single-
species and in a six-species mixture in Central North Dakota in
2006 (Brown, 2011).
Cover crop species Dry matter
kg/ha–1
Oilseed radish (Raphanus sativus L.) 1410
Purple top turnip (Brassica rapa L.) 1695
Pasja turnip [B. rapa (L.); syn. B. campestris]2320
Soybean [Glycine max (L.) Merr.] 1675
Cowpea [Vigna unguiculata (L.) Walp.] 2145
Lupin (Lupinus angustifolius L.) 1380
Six-species mixture (one-half seeding rate)† 5359
Six-species mixture (full seeding rate) 4870
† Millet (Panicum miliaceum L.), cowpea, sunower (Helianthus annuus
L.), soybean (Glycine max L. Merrill), turnip, oilseed radish.
2050 Agronomy Journal • Volume 107, Issue 6 • 2015
Soil water was measured at the center of each plot in 0.3-m
intervals using a neutron probe (Model 503 Hydroprobe, CPN
International, Martinez, CA) at all locations. At Akron the
depth intervals were 0.3 to 0.6 m, 0.6 to 0.9 m, 0.9 to 1.2 m, 1.2
to 1.5 m, and 1.5 to 1.8 m. Soil water in the 0.0 to 0.3 m surface
layer was determined using time-domain reectometry (Trase
System I, Soil Moisture Equipment Corp., Santa Barbara, CA)
with 0.3-m waveguides installed vertically to average the water
content over the entire layer. At Sidney all soil water measure-
ments were made only with the neutron probe and the lowest
layer measured was 1.2 to 1.5 m (2012) and 0.9 to 1.2 m (2013)
due to the presence of a restricting calcium carbonate layer that
limited access tube insertion depth. e neutron probe was
calibrated against gravimetric soil water samples taken in the
plot area. Gravimetric soil water was converted to volumetric
water by multiplying by the soil bulk density for each depth.
Bulk density was determined from the dry weight of the soil
cores (38 mm diam. by 300 mm length) taken from each depth
at the time of neutron probe access tube installation.
Full-season water use was calculated from the water bal-
ance as the dierence between soil water readings at planting
and cover crop termination plus growing season precipitation.
Precipitation was manually measured daily at all locations at
weather observing sites approximately 300 m from the plot
areas. Runo and deep percolation were assumed to be negligible.
is was considered a reasonable assumption as the slopes in the plot
areas were <1% and visua l observations in the plot areas following
heavy rains did not show evidence of runo. However, there may
have been some deep percolation unaccounted for at Akron in 2013,
especially under the irrigated condition (Nielsen et al., 2015).
Plant biomass samples were collected on the dates and
from the areas shown in Table 5. Samples were oven-dried to
0 g kg–1 moisture content. In 2012 at both Akron and Sidney
and in 2013 at Sidney the biomass samples from the cover crop
mixture treatment at termination had each species separately
weighed to determine the fractional composition of the mix-
ture by weight. e late harvest date at Sidney in 2013 (17 July)
was a consequence of the late planting date (30 April). Water
use eciency of biomass production was calculated as biomass
dry weight divided by growing season water use.
Plant population was measured at Akron on 1 May 2012 and
29 May 2013 with number of plants counted in 1 m of row in
each single-species plot and 2 m of row in each mixture plot.
Plant population was measured for the mixture treatment only
at Sidney on 15 June 2012 and 17 July 2013 at Sidney.
e experiment at Akron included no-till fallow plots in
which no cover crop was planted so that residue cover provided
by the cover crop treatments could be evaluated against the
residue cover provided by the existing proso millet residue.
Residue cover was evaluated at Akron by the method described
by Nielsen et al. (2012) in which four photographs in each plot
were taken with a digital camera held level with the horizon
and at arm’s length to the South of the photographer at mid-
day to minimize shadows. Each digital image was subsequently
analyzed using SamplePoint Measurement Soware v. 1.53
(Booth et al., 2006; USDA-ARS, 2012). e SamplePoint
soware was set to select 64 randomly located points in each
image. e soware operator classied each of the 64 points
as either crop residue or soil. e residue cover percentage was
calculated as the fraction of 64 sample points that overlaid crop
residue. e results from the four areas photographed in each
plot were averaged to give a single value of residue cover for
each plot at each sampling time. Residue cover was evaluated
following cover crop planting (only millet residue was present
at this time), following cover crop termination, and following
wheat planting in 2012 and 2013. An additional measurement
of residue cover was made in 2012 just before wheat planting.
No residue cover measurements were made at Sidney.
Two methods of quantifying cover crop water use eciency
were used: (i) dividing biomass dry weight at termination by
cover crop water use from planting to termination, and (ii)
plotting biomass dry weight against water use for all plot-
level data and eye-tting a water-limited yield “frontier line”
(French and Schultz, 1984; Angus and van Herwaarden, 2001;
Sadras and Angus, 2006; Kirkegaard and Hunt, 2010). e
frontier line was then moved to the right, parallel to itself,
Table 3. Cover crop planting and termination dates, seeding
rates, and mixture composition at Akron, CO, and Sidney, NE.
Planting date
Termination
date Crop†
Seeding
rate
kg ha–1
Akron
27 Mar. 2012 16 June 2012 Rapeseed 7.4
4 Apr. 2013 27 June 2013 Flax 39.2
Oat 94.0
Pea 114.5
Mixture 59.7
Rapeseed 2.3
Flax 4.7
Oat 13.7
Pea 8.9
Lentil 5.9
Common Vetch 4.7
Berseem Clover 1.2
Barley 12.5
Phacelia 2.3
Safower 3.5
Sidney
4 Apr. 2012 15 June 2012 Rapeseed 6.7
30 Apr. 2013 18 July 2013 Flax 39.2
Oat 100.8
Pea 112.0
Mixture 57.1
Rapeseed 2.2
Flax 4.5
Oat 13.1
Pea 8.5
Lentil 5.7
Common Vetch 4.5
Berseem Clover 1.1
Barley 11.9
Phacelia 2.2
Safower 3.4
† Rapeseed (Brassica napus L.), Flax (Linum usitatissimum L.), Oat (Avena
sativa L.), Pea (Pisum sativa L.), Lentil (Lens culinaris L.), Common Vetch
(Vicia sativa L.), Berseem Clover (Trifolium alexandrinum L.), Barley
(Hordeum vulgare L.), Phacelia (Phacelia tanacetifolia L.), Safower
(Carthamus tinctorius L .).
Agronomy Journal • Volume 107, Issue 6 • 2015 2051
Table 4. Monthly precipitation (P) at Akron CO, and Sidney NE, during the experimental period and long-term averages (Pavg). Also
shown are irrigation amounts applied at each site. Growing season amounts are only those amounts accumulated between crop emer-
gence and termination.
Year Month
Akron Sidney
P Pavg† Irrigation P Pavg‡ Irrigation
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– m m ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
2012 April 42 42 51 57 41 0
May 41 73 87 22 73 38
June 67 62 16 28 80 51
Growing season 85 155 71 44
2013 April 57 42 8 –§ – –
May 40 73 82 81 73 25
June 72 62 87 74 80 28
July – – – 100 66 0
Growing season 178 177 109 41
† 1908 to 2013.
‡ 1946 to 2013.
§ “–” indicates a time when the cover crop was not present.
Table 5. Cover crop biomass sampling dates and area at Akron, CO, and Sidney, NE.
Location Year Sampling date Sample area Method
m2
Akron 2012 15 May 0.203 Hand harvest
1 June 0.203 Hand harvest
13 June 0.203 (single species)
0.406 (mixture)
Hand harvest
2013 26 June 8.13 Machine harvest
Sidney 2012 1 June 0.254 Hand harvest
15 June 0.508 Hand harvest
2013 17 July 0.254 Hand harvest
Table 6. Cover crop plant populations and fractional composition of mixture total weight at termination Akron, CO, and Sidney, NE.
Cover crop
Akron
2012
Dryland
Akron
2012
Irrigated
Akron
2013
Dryland
Akron
2013
Irrigated
Sidney
2012
Dryland
Sidney
2012
Irrigated
Sidney
2013
Dryland
Sidney
2013
Irrigated
Plant population, 1000 plants ha-1
Rapeseed 1316 1107 897 676
Flax 3296 3308 1254 984
Oat 2583 2841 2201 1992
Pea 885 922 381 418
Mixture 2792 3468 403 323 1175 1468 3365 3060
Fractional composition of mixture total weight, %
Rapeseed 1.5 1.2 0.0 0.0 3.3 0.2
Flax 1.8 1.9 2.3 1.9 0.1 0.3
Oat 33.4 36.6 32.2 37.7 53.5 57.7
Pea 3.9 1.4 4.4 6.4 0.4 1.8
Lentil 1.6 0.7 1.7 1.6 0.5 4.2
Common vetch 2.2 0.6 1.1 0.9 1.7 1.5
Berseem clover 0.1 0.1 0.0 0.3 0.0 0.0
Barley 36.3 35.1 50.8 40.5 38.1 26.3
Phacelia 4.8 5.9 1.0 3.7 0.1 0.8
Safower 4.8 8.8 6.5 6.9 0.0 0.1
Pigweed 0.0 0.1 0.0 0.0 0.1 1.2
Kochia 4.3 2.1 0.0 0.0 0.1 2.8
Russian thistle 4.9 5.1 0.0 0.0 0.0 0.0
Proso millet 0.4 0.4 0.0 0.0 1.9 3.1
Wheat 0.0 0.0 0.0 0.0 0.2 0.0
2052 Agronomy Journal • Volume 107, Issue 6 • 2015
until 10 points in each plot of dry matter vs. water use were
intercepted and those 10 points were used to determine linear
regression equations that dened the water-limited yield rela-
tionship. e regressions were performed with Statistix 10 so-
ware (Analytical Soware, Tallahassee, FL) and the same so ware
was used to compare regression lines for signicant dierences
between slopes and intercepts as indicators of dierences in water
use eciency.
Analysis of variance for cover crop water use, biomass dry
weight, water use eciency, and residue cover was performed
with Statistix 10 soware. Statistically sig nicant dierences in
cover crop water use, biomass dry weight, and water use eciency
were determined by the Tukey HSD mean separation test (a = 0 .05)
when the analysis of variance indicated signicant treatment eects.
RESULTS
Precipitation
e precipitation received during the growing seasons at
the various locations during the 2 yr of the study ranged from
71 mm at Sidney in 2012 to 178 mm at Akron in 2013 (Table
4). e sum of growing season precipitation plus irrigation
ranged from 115 mm at Sidney in 2012 to 355 mm at Akron in
2013. ese conditions provided a broad range of water avail-
ability for quantifying cover crop dry matter production and
water use eciency and comparing these quantities for the four
single-species plantings against the 10-species mixture.
Plant Populations
Plant populations at Akron in 2012 were greatest for ax
and the mixture (Table 6) and least for pea. Much lower plant
stands were observed at Akron in 2013 than in 2012 due to
cold conditions in April following planting that delayed begin-
ning plant emergence for 21 d as noted by Nielsen et al. (2015),
likely resulting in seed depredation. Plant population of oat in
2013 at Akron was least aected by these cool temperatures
and delayed emergence. Irrigation did not consistently improve
plant stands across cover crop species in either year.
Plant populations were only available for the mixture treatment
at Sidney. In 2012 the population of the mixture was less than half
of the population observed at Akron. e 2013 Sidney population
was more than twice the population obtained in 2012.
Biomass, Water Use, and Water
Use Efciency
Ak ron (2012)
e cover crop biomass, water use, and water use eciency
results (Table 7) are presented as individual analyses by loca-
tion and year and water treatment due to signicant interac-
tions (Table 8). e water use of all ve cover crop treatments
were statistically the same (average 136 mm) for the dryland
treatment at Akron in 2012, but ranged from 127 mm for pea
to 147 mm for the mixture. Biomass dry weight ranged from
2920 kg ha–1 for rapeseed to 4190 kg ha–1 for the mixture. e
mixture biomass was signicantly greater than rapeseed, but
statistically the same as for the other single-species plantings.
Both water use and biomass were greater under irrigation at
Akron in 2012. Water use was not dierent among the cover
crop treatments and averaged 252 mm. Biomass under irriga-
tion ranged from 4590 kg ha–1 for rapeseed to 5880 kg ha–1 for
Table 7. Cover crop water use, biomass dry weight, and water
use efciency at termination at Akron, CO, and Sidney, NE.
Water
treatment Crop
Water
use
Dry
weight
Water use
efciency
mm kg ha–1 kg ha–1 mm–1
Akron, CO, 2012
Dryland Flax 136a 3040ab 22.4a
Oat 136a 3460ab 25.4a
Pea 127a 3300ab 26.0a
Rapeseed 135a 2920b 21.6a
Mixture 147a 4190a 28.5a
P0.58 0.04 0.22
Irrigated Flax 258a 5210a 20.2a
Oat 250a 5880a 23.5a
Pea 239a 5420a 22.7a
Rapeseed 257a 4590a 17.9a
Mixture 256a 5670a 22.1a
P0.19 0.25 0.24
Akron, CO, 2013
Dryland Flax 171b 1630b 9.5ab
Oat 252a 3540a 14.0a
Pea 188ab 2400ab 12.8ab
Rapeseed 221ab 1920b 8.7b
Mixture 178b 2020b 11.3ab
P 0.02 <0.01 0.02
Irrigated Flax 277abc 3090b 11.2a
Oat 332a 5630a 17.0a
Pea 313ab 3230b 10.3a
Rapeseed 258bc 2780b 10.8a
Mixture 230c 2630b 11.4a
P<0.01 <0.01 0.05
Sidney, NE, 2012
Dryland Flax 99b 1940ab 19.7a
Oat 140ab 2560a 18.3a
Pea 122ab 2510a 20.6a
Rapeseed 134ab 1370b 10.2b
Mixture 143a 2540a 17.8a
P0.04 <0.01 <0.01
Irrigated Flax 165ab 2860b 17.3b
Oat 185a 4230ab 22.9ab
Pea 158b 4400a 27.8a
Rapeseed 163ab 3070ab 18.8ab
Mixture 164ab 3770ab 23.0ab
P0.04 0.02 0.03
Sidney, NE, 2013
Dryland Flax 204b 3010c 14.8a
Oat 252ab 5160a 20.5a
Pea 245ab 4990a 21.4a
Rapeseed 271a 3170bc 11.7a
Mixture 258a 4790ab 18.6a
P0.01 >0.01 0.05
Irrigated Flax 233b 2920b 12.5a
Oat 287ab 4840ab 16.9a
Pea 274ab 5130ab 18.7a
Rapeseed 312a 4400ab 14.1a
Mixture 278ab 5590a 20.1a
P0.02 0.03 0.17
Agronomy Journal • Volume 107, Issue 6 • 2015 2053
oat, but was statistically the same for all cover crop treatments.
Averaged over all cover crop treatments, the additional 155 mm
of water added as irrigation to simulate the average precipita-
tion condition of south-central Nebraska increased water use by
85% and biomass by 58%. Water use eciency under both water
treatments was not dierent among the cover crop treatments,
averaging 24.8 kg ha–1 mm–1 for the dryland treatment and
21.3 kg ha–1 mm–1 for the irrigated treatment.
e fractional composition (by weight) of the mixture in
2012 was dominated by the two grasses (Table 6). Oat and
barley comprised 69.7% of the dryland mixture biomass and
71.7% of the irrigated biomass. e legumes (pea, lentil, vetch,
and clover) comprised 7.8% of the dryland mixture biomass,
but only 2.8% of the irrigated mixture biomass.
Ak ron (2013)
Average cover crop water use at Akron in 2013 for the dry-
land treatment was greater (202 mm) than in 2012 (136 mm)
due to the doubling of growing season precipitation (85 mm in
2012, 178 mm in 2013). e lowest water use was observed for
ax and the mixture (about 175 mm) and the highest for oat
(252 mm). Dryland biomass production was greatest for oat
(3540 kg ha–1) and least for ax (1630 hg ha–1). e biomass
production of the mixture (2020 kg ha–1) was only signicantly
dierent from the biomass of oat. Even though growing season pre-
cipitation and water use were greater in 2013 than in 2012, average
2013 dryland biomass production was only 68% of the average 2012
production due to the reduced plant sta nds mentioned earlier.
As in 2012, irrigation increased both water use and bio-
mass in 2013. Water use was least for the mixture (230 mm)
and greatest for oat (332 mm). is low value for the mixture
was a consequence of the very low plant population estab-
lished (323,000 plants ha–1) which was only 9.3% of the 2012
population (3,468,000 plants ha–1). Biomass was again greatest
for oat (5630 kg ha–1) which was signicantly greater than all
of the other cover crop treatments (averaging 2930 kg ha–1).
Because of these poor plant stands, water use eciency was
much lower in 2013 than in 2012. Greatest water use eciency
under both dryland and irrigated treatments was observed for
oat (14.0 kg ha–1 mm–1 and 17.0 kg ha–1 mm–1, respectively).
Under both dryland and irrigated treatments the water use e-
ciency of the mixture was about 11.4 kg ha–1 mm–1, which was
not dierent from any of the other single-species cover crops.
Sidney (2012)
Water use for the dryland plots at Sidney in 2012 ranged
from 99 mm for ax to 143 mm for the mixture (Table 7). e
biomass dry weight was statistically the same for ax, oat, pea,
and the mixture, averaging 2390 kg ha–1. Rapeseed produced
1370 kg ha–1. Water use for the irrigated treatment ranged
from 158 mm for pea to 185 mm for oat. Biomass ranged from
2860 kg ha–1 for ax to 4400 kg ha–1 for pea which was not
signicantly dierent from the biomass produced by oat, rape-
seed, or the mixture. Water use eciency under the dryland
condition was the same for ax, oat, pea, and the mixture (aver-
age 19.1 kg ha–1 mm–1) which was signicantly greater than for
rapeseed (10.2 kg ha–1 mm–1). Under irrigation the water use
eciency was greatest for pea (27.8 kg ha–1 mm–1) and least for ax
(17.3 kg ha–1 mm–1). e water use eciency of the mi xture was not
signicantly dierent from any of the single-species plantings.
As observed at Akron, the fractional composition (by
weight) of the mixture in 2012 was dominated by the two
grasses (Table 6). Oat and barley comprised 83.0% of the dry-
land mixture biomass and 78.2% of the irrigated biomass. e
legumes (pea, lentil, vetch, and clover) comprised 7.2% of the dry-
land mixture biomass and 9.2% of the irrigated mixture biomass.
Table 8. Analysis of variance tables for cover crop water use, biomass dry weight , and water use efciency. The main effect, Environment,
was the classication of data as coming from a specic combination of location (Akron, CO or Sidney, NE), year (2012 or 2013), and water
availability treatment (dryland or irrigated). Environment was treated as a random variable and cover crop was treated as a xed variable.
Source df SS MS F P
Water use
Environment 7 437,672 62,524.6 12.11 <0.001
Environment × Rep 24 123,919 5,163.3
Cover crop 4 24,067 6,016.8 3.15 0.029
Environment × Crop 28 53,468 1,909.6 4.07 <0.001
Environment × Rep × Crop 96 45,046 469.2
Total 159 684,173
Biomass dry weight
Environment 7 1.352 × 1081.932 × 1079.32 <0.001
Environment × Rep 24 4.976 × 1072.073 × 106
Cover crop 4 5.050 × 1071.262 × 1079.45 <0.001
Environment × Crop 28 3.742 × 1071.336 × 1062.69 <0.001
Environment × Rep × Crop 96 4.768 × 1074.966 × 105
Total 159 3.206 × 108
Water use efciency
Environment 7 3,098.9 442.7 12.80 <0.001
Environment × Rep 24 830.1 34.6
Cover crop 4 885.6 221.4 10.01 <0.001
Environment × Crop 28 619.2 22.1 2.21 0.002
Environment × Rep × Crop 96 1,305.0 13.6
Total 159 6,738.8
2054 Agronomy Journal • Volume 107, Issue 6 • 2015
Sidney (2013)
As at Akron, dryland cover crop water use in 2013 was
greater than in 2012 due to greater precipitation (54% greater),
resulting in greater dryland biomass (Table 7). Water use was
least for ax (204 mm) and greatest for rapeseed (271 mm),
which was not signicantly dierent from the water use
observed for oat, pea, and the mixture. Dryland biomass ranged
from 3010 kg ha–1 for ax to 5160 kg ha–1 for oat, which was not
signicantly dierent from pea, rapeseed, or the mixture.
Under the irrigated condition ax was again the lowest
water using crop (233 mm) while rapeseed used the most water
(312 mm). e least biomass was produced by ax (2920 kg ha–1)
while the mixture produced the most biomass (5590 kg ha–1),
which was not dierent from oat, pea, or rapeseed.
Water use eciency under the dryland treatment ranged
from 11.7 kg ha–1 mm–1 for rapeseed to 20.5 kg ha–1 mm–1
for oat, but the dierences were not signicant. Water
use eciency for the irrigated treatment ranged from
12.5 kg ha–1 mm–1 for ax to 20.1 kg ha–1 mm–1 for the mix-
ture, but again the dierences were not signicant.
e fractional composition (by weight) of the mixture in
2013 was even more dominated by the two grasses (Table 6).
Oat and barley comprised 91.6% of the dryland mixture bio-
mass and 84.0% of the irrigated biomass. e legumes (pea,
lentil, vetch, and clover) comprised 2.6% of the dryland mix-
ture biomass and 7.5% of the irrigated mixture biomass.
Water-Limited Yield Potential
As stated earlier, plots of water use vs. biomass can identify
the water-limited yield potential (French and Schultz, 1984).
We graphed our individual plot data aer this manner and
eye-t a data frontier line (black line, Fig. 1). As is usually the
case in crop production, there are factors other than water
availability that cause yield to fall below and to the right of the
frontier line. e most easily identied factor in the current
dataset was the poor plant establishment in 2013 at Akron
due to the abnormally cold April temperatures that delayed
emergence. Additionally, hailstorms at Akron on 23 and 24
June 2013 also reduced harvestable biomass, particularly of
rapeseed (visual observation). e linear regressions (red lines,
Fig. 1) t to the 10 data points nearest to the eye-t frontier line
dene the water-limited yield potentials and allow for another
comparison of the water use eciency of the cover crop treat-
ments. e greatest regression slope (27.26 kg ha–1 mm–1) and
consequently the greatest water use eciency was observed
for oat (Table 9), which was not signicantly dierent from
the mixture (23.53 kg ha–1 mm–1), but was dierent from pea
(18.28 kg ha–1 mm–1), ax (17.69 kg ha–1 mm–1), and rapeseed
(16.93 kg ha–1 mm–1). e ax slope was not signicantly dif-
ferent from the pea, rapeseed, and mixture slopes.
A greater intercept of the water-limited yield regression line
could be interpreted as an indication of potentially greater
biomass production under low water availability conditions.
e regression intercept was greatest for pea (1607 kg ha–1)
and least for oat (400 kg ha–1). e intercepts for oat and the
mixture were not dierent from each other. e intercepts for
ax and rapeseed were also not dierent from each other, and
neither were the intercepts for the mixture and pea.
When the regression slopes are ordered from smallest to largest
they rank as rapeseed, a x, pea, mixture, and oat. is is the order
that would be expected based on the energy requirements to produce
dierent plant compositions (e.g., starch, protein, oil; Tanner and
Sinclair, 1983). In other words, we would expect greater water use
eciency from a grass (oat) and a grass-dominated mixture tha n we
would from a legume (pea) or from an oilseed (ax, rapeseed).
As a point of comparison with previous research, we have
calculated water use and yield points for oat and rapeseed (Fig.
1, yellow points) from the water requirement values published
by Briggs and Shantz (1913). ose calculated points indicated
that Briggs and Shantz found a lower water use eciency for
oat but a similar water use eciency for rapeseed.
Residue Cover
Residue cover measurements taken at Akron following cover
crop planting showed the proso millet residue provided about
85% cover in 2012 and 73% cover in 2013 (Fig. 2). Following
cover crop termination in 2012 the dryland residue cover
declined for the proso millet fallow treatment to 73%, which was
similar to ax (73%), pea (75%), and the mixture (78%) residue
cover. Oat (81%) had maintained the original residue cover
percentage, but rapeseed had declined to 65%. Under the irri-
gated treatment in 2012, residue cover was maintained at more
than 80% for rapeseed, oat, pea, and the mixture, but declined to
74% for ax and 68% for the fallow millet residue. Residue cover
continued to decline for all treatments with time to wheat plant-
ing for both water availability conditions, with the greatest cover
seen for oat and the mixture. ere was a rapid loss of residue
cover following wheat planting in 2012 due to the action of the
grain drill, with an average loss across cover crop treatments and
water availability conditions of 16 percentage points. e least
loss in residue cover due to planting the wheat was seen for oat
(74% declining to 71%, averaged over irrigation treatments).
Fig. 1. Water use and biomass dry weight of flax, oat, pea,
rapeseed, and a 10-species mixture of cover crops grown at
Akron, CO, and Sidney, NE, in 2012 and 2013.
Agronomy Journal • Volume 107, Issue 6 • 2015 2055
Table 9. Slopes and intercepts of linear regression lines t to the 10-point data frontier of water use vs. dry matter production for cover
crops grown at Akron, CO, and Sidney, NE, in 2012 and 2013, and matrices of regression slope and intercept comparison statistics. Also
shown for comparison with the slopes are the biomass productivity (gram seed per gram of photosynthate) values computed by Sinclair
and de Wit (1975).
Regression slopes and intercepts
Species Slope Intercept R2Biomass productivity
kg ha–1 mm–1 kg ha–1 g g–1
Flax 17.69 1018 0.98 0.46
Oat 27.26 400 0.96 0.70
Pea 18.28 1607 0.86 0.65
Rapeseed 16.93 1128 0.96 0.43
Mixture 23.53 995 0.93 –
Matrices of regression slope and intercept comparisons. Matrix values are the probability that the null hypothesis (slopes [or intercepts]
of the data frontier water-limited yield regression lines are equal) is true.
Regression slope comparison
Flax Oat Pea Rapeseed
Oat <0.01
Pea 0.82 0.02
Rapeseed 0.59 <0.01 0.63
Mixture 0.08 0.37 0.23 0.07
Regression intercept comparison
Flax Oat Pea Rapeseed
Oat <0.01
Pea <0.01 0.47
Rapeseed 0.96 <0.01 <0.01
Mixture <0.01 0.37 0.80 <0.01
Fig. 2. Residue cover of fallow and cover crops following proso millet fallow at Akron, CO, in 2012 and 2013. Rapeseed, flax, oat, and pea
were grown as single-species plantings. The mixture was composed of 10 species.
2056 Agronomy Journal • Volume 107, Issue 6 • 2015
In 2013, where the starting proso millet fallow residue was
lower (73%) than in 2012, oat under the dryland treatment
increased residue cover to 82% at cover crop termination while
over the same period the proso millet fallow residue declined
to 63%. e residue covers provided by the other crops were
observed to be 75% for rapeseed, 69% for the mixture and pea,
and 62% for ax. Following wheat planting the residue cover
provided by oat still remained high (74%) while all of the other
treatments were reduced by weathering and the action of the
grain drill to between 23% (fallow) and 32% (ax). e greater
cover crop biomass produced under irrigation in 2013 (Table
7) resulted in increases in residue cover at the time of cover
crop termination compared with the cover crop residue follow-
ing cover crop planting. e greatest cover was again seen for
the oat residue (92%), followed by pea (82%), rapeseed (78%),
mixture (77%), and ax (75%). e millet residue had declined
to 54% by the time of cover crop termination. Following wheat
planting, the oat residue covered 72% of the ground while ax,
pea, and mixture residues covered about 33% of the ground.
e poorest residue cover following wheat planting was noted
for ax and fallow (18%).
DISCUSSION
No dierences were seen that would indicate consistently
greater biomass production or greater water use eciency by the
10-species mixture than by any of the single-species plantings of
cover crops. e water use eciency values reported in Table 7
vary widely from 8.7 to 28.5 kg ha–1 mm–1, likely depending on
factors such as timing and amount of precipitation and irriga-
tion, temperature stress, plant stand, hail, photosynthetic car-
boxylation pathway, and diering energy requirements to make
starch, protein, or oil. erefore a better method for determining
dierences in water use eciency that may arise due to synergis-
tic eects of mixing cover crop species is the use of the frontier
analysis of French and Schultz (1984). e slopes identied in
Table 9 for the water-limited yield lines of the single-species
plantings rank in the same order as the biomass productivity
(gram of seed per gram of photosynthate) calculated by Sinclair
and de Wit (1975), also shown in Table 9, from the values of glu-
cose conversion into carbohydrates, protein, or lipids provided by
Penning de Vries (1975). at similarity in ranking (rapeseed <
ax < pea < oat) gives us condence that the slope of the regres-
sion line of the mixture (intermediate to the slope of oat and pea)
is a true reection of the mixed photosynthetic productivities of
the grasses, legumes, and oilseeds that make up the mixture. We
can conclude with certainty that for this study growing the cover
crops in a mixture did not change the basic chemistry and phys-
ics of the photosynthetic process into a more ecient plant pro-
cess than occurs with single-species plantings. is conclusion is
based on the observation that the slope of the mixture regression
line was not greater than the slope of the oat line and was inter-
mediate to the slopes for oat and pea. Because the experiment
was established in a new area each year at both sites, the study
is not able to address if longer-term use of cover crop mixtures
might lead to improvements in water use eciency.
e fractional composition of the mixture by seeding rate
weight was 44% grasses, 35% legumes, and 18% oilseeds (Table
3). At termination the fractional composition of the mixture
(by biomass weight) averaged 80% grasses, 6% legumes, and 7%
oilseeds (Table 6). ere is quite a bit of variability from year
to year and between sites as to which of the oilseeds and which
of the legumes were dominant in the mixture, but clearly the
grasses were more competitive than the legumes and oilseeds.
Because water use eciency of biomass production was not
improved with the mixture compared with single-species plant-
ings of grasses, there may be little justication for incorporat-
ing legumes and oilseeds into a cover crop planting for the sake
of diversity if the primary purpose is to provide biomass for
cover and erosion protection. However, if the primary purpose
of the cover crop is to provide some forage production for
livestock feed, then inclusion of legumes and oilseeds to obtain
a specic forage quality may need to be considered.
Previous research (Nielsen and Vigil, 2005) has shown that
spring-planted cover crop water use in this semiarid environ-
ment will depress yields of subsequent wheat crops planted
70 to 100 d following cover crop termination, with that yield
depression ranging from 905 to 1650 kg ha–1. erefore, most
farmers will need to receive some economic benet from the
cover crop to pay for the cover crop seed, planting costs, and
the yield depression they are likely to experience because of
the cover crop water use. at benet may come from taking
a portion of the cover crop as forage or grazing o a portion of
the cover crop. Determining how much of the cover crop can
be removed while still maintaining sucient cover to provide
adequate erosion control and soil organic matter levels is a com-
plex problem with highly variable answers depending on soil
type, weather, and existing levels of organic matter (Wilhelm
et al., 2004; Andrews, 2006). Data from the current study
show widely ranging amounts of cover crop biomass produced
(1366 to 5880 kg ha–1) depending primarily on available grow-
ing season water, cover crop species, and plant stands. Residue
cover amounts at Akron following cover crop termination time
ranged from 62 to 92% (Fig. 2), which appears to be more than
enough to allow for some biomass removal and still maintain
enough cover for wind erosion protection (Fryrear, 1985;
Williams et al., 1997). However, even without grazing, the
residue cover percentages declined over time until wheat plant-
ing, and in 2013 when plant stands were poor, the residue cover
following wheat planting was far below 60% for all treatments
except oat, which should give some concern regarding soil
erosion potential. Growing the cover crop helped to maintain
residue cover at greater amounts than the constantly weather-
ing and declining millet residue, with oat residue providing the
most cover in 2013 because of the better plant stand observed
for oat compared with the other treatments. Further studies are
likely needed to evaluate changes in residue cover that follow graz-
ing and the economics associated with managed grazing practices.
CONCLUSIONS
Cover crops serve useful purposes in improving both soil
structure and organic matter and also in reducing wind and
water erosion potential. ese benecial eects are more likely
to be seen in more humid regions of the United States where
lack of precipitation that limits biomass production does not
frequently occur. In contrast, the Central Great Plains region
oen has dryland biomass production limited by available
water and consequently may not produce enough biomass to
allow for protable grazing while still maintaining erosion
Agronomy Journal • Volume 107, Issue 6 • 2015 2057
protection and soil organic matter levels. Growing cover crops
in mixtures does not improve the water use eciency of bio-
mass production. e added expense generally seen for cover
crop mixtures compared with single-species plantings (Nielsen
et al., 2015) is therefore not likely to be justied. Where previ-
ous crop residues are insucient to provide erosion protection
and a cover crop must be employed to provide ground cover,
inexpensive monocultures are recommended. Cover crop
mixtures may be justied if a portion of the biomass produced
is to be grazed and if a certain desired forage quality can be
produced by proper mixture selection, but growing a cover crop
mixture is not likely to produce greater biomass than a single-
species planting.
ACKNOWLEDGMENTS
The authors acknowledge the important contributions made to
this study by Jamie Sauer, David Poss, Alexis Thompson, Shelby Guy,
Shelby Dunker, Tyler Schumacher, Jeremy Reimers, and Amanda
McKay. Green Cover Seed, Bladen, NE , recommended the composi-
tion of the 10-species mixture and graciously provided the seed for
the first year of the study.
REfERENCES
Aase, J.K., and J.L. Pikul, Jr. 2000. Water use in a modied summer
fallow system on semiarid northern Great Plains. Agric. Water
Mana ge. 4 3:345 –357. doi:10.1016/S 0378-3774(99)0 0062-1
Andrews, S. S. 2006. Crop residue removal for biomass energy produc-
tion: Eects on soils and recommendations. NRCS White Paper.
NRCS. www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/
nrcs142p2_053255.pdf (accessed 13 Mar. 2015).
Angus, J.F., and A.F. van Herwaarden. 2001. Increasing water use and
water use eciency in dryland wheat. Agron. J. 93:290–298.
doi:10.2134/agronj2001.932290x
Berns, K., and B. Berns. 2009. Cover crop water usage and aect
(sic) on yield in no-till dryland cropping systems, nal report.
SARE, USDA. http://mysare.sare.org/MySare/ProjectReport.
aspx?do=viewProj&pn=FNC07-653 (accessed 27 July 2015).
Blanco-Canqui, H., J.D. Holman, A.J. Schlegel, J. Tatarko, and T.M.
Shaver. 2013. Replacing fa llow with cover crops in a semiar id soil:
Eects on soil properties. Soil Sci. Soc. Am. J. 77:1026–1034.
doi:10. 2136/sssaj2013.01. 0006
Booth, D.T., S.E. Cox , and R.D. Berr yman. 2006 . Point sampl ing digi-
tal imagery with ‘SamplePoint’. Environ. Monit. Assess. 123:97–
108. doi:10.10 07/s10661-005-9164 -7
Briggs, L.E., and H.L. Shantz. 1913. e water requirement of plants.
I. Investigations in the Great Plains in 1910 and 1911. BPI Bull.
294. U.S. Gov. Print. Oce, Washington, DC.
Briggs, L.E., and H.L. Shantz. 1917. e water requirement of plants
as inuenced by environment. Proc. 2nd Pan-Am Sci. Congr.
3:95–107. Bureau of Plant Industry, Washington, DC.
Brown, G. 2011. Working towards sustainability. Conservation Cov-
ers: Eective Cover Cropping in the Midwest, Concurrent Ses-
sion F, Decatur, IL. 7–8 Dec. 2011. Soil and Water Conserv. Soc.
http://vimeo.com/3 4348855 (accessed 1 Mar. 2015).
Brown, P. 1971. Water use and soil water depletion by dryland winter
wheat as aected by nitrogen fertilization. Agron. J. 63:43–46.
doi:10.2134/agronj1971.00021962006300010015x
Cardinale, B.J., J.P. Wright, M.W. Cadotte, I.T. Carroll, A. Hector,
D.S. Srivastava et al. 2007. Impacts of plant diversity on biomass
production increase through time because of species complemen-
tarity. Proc. Natl. Academy Sci. 104:18123–18128.
Carr, P.M., R.D. Horsley, and W.W. Poland. 2004. Barley, oat, and
cereal-pea mixtures as dryland forages in the northern Great
Plains. Agron. J. 96:677–684. doi:10.2134/agronj20 04.0677
Carr, P.M., G.B. Martin, J.S. Caton, and W.W. Poland. 1998. Forage
and nitrogen yield of barley-pea and oat-pea intercrops. Agron. J.
90:79–84. doi:10.2134/agronj1998.00021962009000010015x
Chen, C., M. Westcott, K. Neill, D. Wichman, and M Knowx. 2004.
Row conguration and nitrogen application for barley-pea inter-
cropping in Montana. Agron. J. 96:1730–1738.
Clark, A. 2012. Managing cover crops protably. 3rd ed. Handbook
Series Book 9. Sustainable Agric. Res. and Education, Univ.
Maryland, College Park. http://www.sare.org/Learning-Cen-
ter/Books/Managing-Cover-Crops-Profitably-3rd-Edition
(accessed 1 Mar. 2015).
Droushiotis, D.N. 1989. Mixtures of annual legumes and small-
grained cereals for forage production under low rainfall. J. Agric.
Sci. Cambr idge 113:249–253. doi:10.1017/S0021859600086 834
Dunavin, L.S., Jr. 1987. Comparison of turnip-Chinese cabbage
hybrid, rape, and rye, alone and in combination with annual rye-
grass and crimson clover. Agron. J. 79:591–594. doi:10.2134/agr
onj1987.00021962007900040001x
Farnsworth, R.K., E.L. Peck, and E.S. ompson. 1982. Evaporation
atlas for t he contig uous 48 United States. NOAA Tech. Rep. NW S
33: U.S. Dep. Commerce-NOAA-NWS, Washington, DC.
Franzluebbers, A.J., and J.A. Stuedemann. 2008. Soil physical
responses to cattle grazing cover crops under conventional and
no tillage in the Southern Piedmont USA. Soil Tillage Res.
100:141–153. doi:10.1016/j.still .200 8.05. 011
French, R.J., and J.E. Schultz. 1984. Water use eciency of wheat
in a Mediterranean-type environment. I. e relation between
yield, water use and climate. Aust. J. Agric. Res. 35:743–764.
doi:10.1071/AR984 0743
Fryrear, D.W. 1985. Soil cover and wind erosion. Trans . ASAE 28:781–
784. doi:10.13031/2013.32337
Kirkegaard, J.A., and J.R. Hunt. 2010. Increasing productivity by
matching farming system management and genotype in water-
limited environments. J. Exp. Bot. 61:4129–4143. doi:10.1093/
jx b/erq2 45
Kohler, M.A., T.J. Nordenson, and D.R. Baker. 1959. Evaporation
maps for the United States . Tech. Paper 37. U.S. Dep. Commerce.
U.S. Gov. Print. Oce, Washington, DC.
Kramer, P.J. 1983. Drought tolerance and water use eciency. In: P.J.
Kramer, editor, Water relations of plants. Academic Press, New
York. p. 390–474.
LaChance, J., and B. Bradley. 2014. How the CCCs add up: A 2yr bio-
mass review. In: J. LaChance, editor, Cover crop cocktail hour.
Pennsylvania State Univ. Ext. http://agsci.psu.edu/organic/
research-and-extension/cover-crop-cocktails/project-summary
(accessed 1 Mar. 2015). p. 2–3.
Lal, R., E. Regnier, D.J. Eckert, W.M. Edwards, and R. Hammond.
1991. Expectations of cover crops for sustainable agriculture.
In: W.L. Hargrove, editor, Cover crops for clean water. Soil and
Water Conserv. Soc., Ankeny, IA.
Lenssen, A.W., S.D. Cash, P.G. Hateld, U.M. Sainju, W.R. Grey,
S.L. Blodgett et al. 2010. Yield, quality, and water and nitrogen
use of durum and annual forages in two-year rotations. Agron. J.
102:1261–1268. doi:10.2134/agronj2010.0078
Miller, P.R., R.E. Engel, and J.A. Holmes. 2006. Cropping sequence
eect of pea and pea management on spring wheat in the north-
ern Great Plains. Agron. J. 98:1610–1619.
Miller, P.R., B.G. McConkey, G.W. Clayton, S.A. Brandt, J.A. Star-
icka, A.M. Johnston et al. 2002. Pulse crop adaptation in the
northern Great Plains. Agron. J. 94:261–272. doi:10.2134/
agronj2002.0261
2058 Agronomy Journal • Volume 107, Issue 6 • 2015
Nielsen, D.C. 2001. Production functions for chickpea, eld pea,
and lentil in the central Great Plains. Agron. J. 93:563–569.
doi:10.2134/agronj2001.933563x
Nielsen, D.C., D.J. Lyon, G.W. Hergert, R.K. Higgins, F.J. Calderon,
and M.F. Vigil. 2015. Cover crop mixtures do not use water dif-
ferently than single-species plantings. Agron. J. 107:1025–1038
10.2134/agronj14.0504. doi:10.2134/agronj14.0504
Nielsen, D.C., J.J. Miceli-Garcia, and D.J. Lyon. 2012. Canopy cover
and leaf area index relationships for wheat, triticale, and corn.
Agron. J. 104:1569–1573. doi:10.2134/agronj2012.0107n
Nielsen, D.C., and M.F. Vigil. 2005. Legume green fallow eect on
soil water content at wheat planting and wheat yield. Agron. J.
97:684–689. doi:10.2134/agronj2004.0071
Nielsen, D.C., M.F. Vigil, and J.G. Benjamin. 2009. e vari-
able response of dryland corn yield to soil water content at
planting. Agric. Water Manage. 96:330–336. doi:10.1016/j.
agwat.2008.08.011
Nielsen, D.C., M.F. Vigil, and J.G. Benjamin. 2011. Evaluating deci-
sion rules for dryland rotation crop selection. Field Crops Res.
120:254–261. doi:10.1016/j.fcr.2010.10.011
Passioura, J.B., and J.F. Angus. 2010. Improving productivity of
crops in water-limited environments. Adv. Agron. 106:37–75.
doi:10.1016/S0065-2113(10)06002-5
Penning de Vries, F.W.T. 1975. Use of assimilates in higher plants. In:
J.P. Cooper, editor, Photosynthesis and productivity in dierent
environments. Cambridge Univ. Press, Cambridge. p. 459–480.
Petrosino, J.S., J.A. Dille, J.D. Holman, and K.L. Roozeboom. 2015.
Kochia suppression with cover crops in southwestern Kansas.
Crop Forage Turfgrass Manage. 1(1). https://dl.sciencesocieties.
org/publications/cm/tocs/1/1 (accessed 27 July 2015).
doi:10.2134/cm2014.0078.
Robinson, C., and D. Nielsen. 2015. e water conundrum of plant-
ing cover crops in the Great Plain: When is an inch not an inch?
Crops & Soils Magazine 48:24–31.
Robinson, R .G. 1960. Oat-pea or oat-vetch mixtures for fora ge or seed.
Agron. J. 52:546 –549. doi:10.2134/agronj1960.00 0219620 0520
0090019x
Sadras, V.O., and J.F. Angus. 2006. Benchmarking water-use e-
ciency of rainfed wheat in dry environments. Aust. J. Agric. Res.
57:847–856. doi:10.1071/AR05359
Sinclair, T.R., and C.T. de Wit. 1975. Photosynthate and nitrogen
requirement s for seed product ion by various crops . Science (Wash-
ington, DC) 189:565–567. doi:10.1126/science.189.4202.565
Sinclair, T.R., and A. Weiss. 2010. Principles of ecology in plant pro-
duction. 2nd ed. CAB Int., Cambridge, MA.
Skidmore, E.L., M. Kumar, and W.E. Larson. 1979. Crop residue
management for wind erosion control in the Great Plains. J. Soil
Water Conserv. 34:90–96.
Skidmore, E.L., and F.H. Siddoway. 1978. Crop residue requirements
to control wind erosion. In: W.R. Oschwald, editor, Crop residue
management systems. ASA Spec. Publ. 31. ASA, Madison, WI.
p. 17–33.
Snapp, S.S., S.M. Swinton, R. Labarta, D. Mutch, J.R. Black, R. Leep,
J. Nyiraneza, and K. O’Neil. 2005. Evaluating cover crops for
benets, costs and performance within cropping system niches.
Agron. J. 97:322–332. doi:10.2134/agronj2005.0322
Stewart, B.A., and G.A. Peterson. 2014. Managing green water
in dryland agriculture. Agron. J. 106:1–10. doi:10.21345/
agronj14.0038).
Tanner, C.B., and T.R. Sinclair. 1983. Ecient water use in crop pro-
duction: Research or re-search? In: H.M. Taylor, W.R. Jordan,
and T.R. Sinclair, editors, Limitations to ecient water use in
crop production. ASA, CSSA, and SSSA, Madison, WI. p. 1–27.
Tilman, D., P.B. Reich, J. Knops, D. Wedin, R. Mielke, and C.
Lehman. 2001. Diversity and productivity in a long-term grass-
land experiment. Science (Washington, DC) 294:843–845.
doi:10.1126/science.1060391
Treadwell, D., N. Creamer, and K. Baldwin. 2010. An introduction to
cover crop species for organic farming systems. http://www.exten-
sion.org/pages/18542/an-introduction-to-cover-crop-species-for-
organic-farm ing-systems#.VNU2sC 7R-eQ (accessed 1 Mar. 2015).
USDA-ARS. 2012. SamplePoint measurement soware 1.54. USDA-
ARS Products and Services. http://ww w.ars.usda.gov/services/
soware/download.htm?sowareid=295 (accessed 13 Mar. 2015).
Wilhelm, W.W., J.M.F. Johnson, J.L. Hateld, W.B. Voorhees, and
D.R. Linden. 2004. Crop and soil productivity response to
corn residue removal: A literature review. Agron. J. 96:1–17.
doi:10.2134/agronj2004.0001
Williams, J.D., D.E. Wilkins, C.L. Douglas, Jr., and R.W. Rickman.
1997. Winter erosion in four residue management systems: Pre-
liminary report. 1997 Columbia Basin Agric. Res. Ann. Report,
Spec. Rep. 977:73–76. Oregon State Univ., Pendleton. www.ars.
usda.gov/sp2UserFiles/person/6112/winterErosionInFour.pdf
(accessed 13 Mar. 2015).
