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AGRONOMY JOURNAL, VOL. 92, JANUARY–FEBRUARY 2000
and yield of soybean as influenced by foliar fertilization. Agron.
J. 72:110–113.
Poole, W.D., G.W. Randall, and G.E. Ham. 1983. Foliar fertilization
of soybean. I. Effect of fertilizer sources, rates, and frequency of
application. Agron. J. 75:195–200.
Rosolem, C.A., J.C.O. Silverio, and O. Primaves. 1982. Adubacao
foliar de soja: II. Efeitos de NPK e micronutrientes (abstract in
English). Pesq. Agropec. Bras. 17:1559–1562.
SAS Institute. 1996. SAS User’s Guide. Version 6. Fourth Edition.
SAS Institute Inc., Cary, NC.
Sesay, A., and Shibles, R. 1980. Mineral depletion and leaf senescence
in soybean as influenced by foliar nutrient application during seed
filling. Ann. Bot. 45:47–55.
Syverud, T.D., L.M. Walsh, E.S. Oplinger, and K.A. Kelling. 1980.
Foliar fertilization of soybean (Glycine max L.). Commun. Soil.
Sci. Plant Anal. 11:637–651.
FORAGES
Binary Legume–Grass Mixtures Improve Forage Yield, Quality,
and Seasonal Distribution
Byron Sleugh,* Kenneth J. Moore, J. Ronald George, and Edward C. Brummer
ABSTRACT
Yield and forage quality of kura clover (Trifolium ambiguum
Bieb.) and intermediate wheatgrass [Thinopyrum intermedium
(Host.) Barkw. & D.R. Dewey] mixtures compared with commonly
grown forages such as alfalfa (Medicago sativa L.) and smooth bromegrass (Bromus inermis Leyss.) have not been fully explored. Our
objective was to evaluate the effects of alfalfa, birdsfoot trefoil (Lotus
corniculatus L.), and kura clover grown in binary mixtures with orchardgrass (Dactylis glomerata L.), smooth bromegrass, and intermediate wheatgrass on seasonal distribution of forage yield and quality.
Plots of each species in monoculture and binary legume–grass mixtures were established in a randomized complete block design in 1994
near Boone, IA. Yield was measured monthly during the 1995 and
1996 seasons. In vitro dry matter digestibility (IVDMD), neutraldetergent fiber (NDF), and crude protein (CP) concentrations were
determined for each monoculture or mixture. Total yield was highest
for monoculture alfalfa, alfalfa–intermediate wheatgrass, and alfalfa–
smooth bromegrass with 13 400, 12 700, and 12 600 kg ha⫺1 respectively in 1995, and 7500, 6800, and 6700 kg ha⫺1 respectively, in 1996.
Kura clover had the lowest NDF (357 g kg⫺1) and highest IVDMD
(740 g kg⫺1) concentrations compared with other forages. Yield, CP,
and IVDMD concentrations of monoculture grasses were lower than
those of the legume–grass mixtures or of the monoculture legumes.
Legumes improved the seasonal distribution of yield and forage quality by beig more productive at later harvests. Yield of alfalfa–
intermediate wheatgrass was equal to or better than other alfalfa–grass
mixtures and could make a valuable legume–grass alternative.
C
ommercial nitrogen fertilizers are essential for
maximizing productivity of cool-season grasses
grown in monoculture. Legumes grown with grasses offer several advantages over grasses grown alone. Baylor
(1974) noted that including legumes usually results in
increased yield, higher quality, and improved seasonal
distribution of forage. Legume–grass mixtures have reduced weed encroachment and erosion and have led to
Dep. of Agronomy, Iowa State University, Ames, IA 50011-1010.
Journal Paper No. J-18184 of the Iowa Agric. and Home Econ. Exp.
Stn., Ames, IA, Project No. 2899, and supported by Hatch Act and
State of Iowa funds. Received 11 Dec. 1998. *Corresponding author
([email protected]).
Published in Agron. J. 92:24–29 (2000).
greater stand longevity than legume or grass monocultures (Droslom and Smith, 1976).
Although exceptions exist, compatible legume–grass
mixtures usually yield more than any single component
grown in monoculture (Roberts and Olson, 1942; Aberg
et al., 1943). Wilsie (1949) noted, however, that alfalfa–
grass mixtures did not yield more forage than alfalfa
alone when alfalfa was seeded at a high rate; Wilsie also
concluded that alfalfa was the best legume to grow with
smooth bromegrass. Even though alfalfa–grass mixtures
have received much acclaim, several studies (Fuelleman
et al., 1943; Rather and Harrison, 1944; Koonce, 1946;
Mooso and Wedin, 1990) concluded that mixtures offer
little yield advantage over alfalfa monocultures when
harvested as hay.
Intermediate wheatgrass has wide adaptation and
high productivity, but is not as widely used as smooth
bromegrass or crested wheatgrass. This may be because
it does not persist for more than 4 to 5 yr, especially
under intense management. It tolerates alkaline and
saline soils and does well with alfalfa under dryland or
limited irrigation conditions (Asay, 1995). Its erect
stems prevent lodging of alfalfa when grown in mixtures,
and it is usually not as advanced in maturity as alfalfa
at harvest. The productivity and forage quality of intermediate wheatgrass grown in mixture with forage legumes such as alfalfa and birdsfoot trefoil in the Midwest has not been fully explored.
Kura clover consistently has lower concentrations of
acid-detergent fiber and acid-detergent lignin (Allinson
et al., 1985), and higher IVDMD (Sheaffer and Marten,
1991) than most other forage legumes, including alfalfa.
These characteristics suggest that kura clover–grass forage mixtures could have lower NDF and higher IVDMD
than alfalfa–grass mixtures. Once established, kura clover is able to withstand extreme environmental conditions such as cold, drought, poor fertility, and waterlogging (Pederson, 1995), and could prove to be a good
substitute for alfalfa or other legumes. Our objective
was to evaluate the effects of birdsfoot trefoil, alfalfa,
Abbreviations: CP, crude protein; IVDMD, in vitro dry matter digestibility; NDF, neutral-detergent fiber.
SLEUGH ET AL.: BINARY LEGUME–GRASS MIXTURES IMPROVE FORAGE YIELD
25
and kura clover on seasonal distributions of yield and
forage quality when grown in binary mixtures with orchardgrass, smooth bromegrass, and intermediate
wheatgrass.
MATERIALS AND METHODS
Plot Establishment
Field studies were conducted at the Iowa State University
Agronomy and Agricultural Engineering Research Farm
(42⬚59⬘ N, 93⬚55⬘ W), on a Webster–Nicollet soil (fine-loamy,
mixed, superactive, mesic Typic Endoaquoll–Aquic Hapludoll). Mean air temperature from April to October was 16.9
and 16.5⬚C for 1995 and 1996, respectively, and mean monthly
precipitation for April to October was 8.5 and 10.5 cm for
1995 and 1996, respectively. Distribution of precipitation for
April to September of 1995 and 1996 is shown in Fig. 1. On
14 Apr. 1994, 1.5- by 7.5-m plots of ‘Dawn’ orchardgrass,
‘Bounty’ smooth bromegrass, and ‘Manska’ intermediate
wheatgrass were planted in monoculture and in binary mixtures with ‘Alfagraze’ alfalfa, ‘Norcen’ birdsfoot trefoil, and
‘Rhizo’ kura clover. Monoculture grasses, birdsfoot trefoil,
and alfalfa were seeded at a rate of 5.4 kg ha⫺1, and monoculture kura clover was seeded at 2.7 kg ha⫺1. In binary mixtures,
each species was seeded at 2.7 kg ha⫺1, except kura clover
mixtures where kura clover was seeded at 1.4 kg ha⫺1. Alfalfa
seeds were treated with the fungicide metalaxyl {[R]-[(2,6dimethylphenyl)-methoxyacetylamino]-propionic acid methyl
ester} before planting. Seedings were made with a small-plot
drill in 10-row units at 15-cm spacing. The drill had dual cones,
and each cone served alternating units, resulting in binary
mixtures of alternating rows of legume and grass. For monoculture seedings, both cones contained seeds of the same species. There were four replications for each treatment. Plots
were not fertilized in the establishment year. However, all
grass monoculture plots were fertilized in early April with N
at 67 kg ha⫺1 in 1995 and 1996 to simulate the small amounts
of N typically applied by forage producers. No P or K fertilizer
was applied, because soil test results indicated that sufficient
amounts were present in the soil. Binary mixtures were not fertilized.
Forage Yield and Quality
Plots were harvested on 12 June, 12 July, 18 Aug., and 6
Nov. 1995 and on 29 May, 2 July, 14 Aug., and 4 Oct. 1996
to coincide with alfalfa in late-bud to one-tenth bloom stage.
The timing of the harvest was based on the alfalfa stage of
maturity so we would have a consistent and systematic way
of timing our harvests. When alfalfa was at one-tenth bloom,
birdsfoot trefoil and kura clover were often still in the late
vegetative stage. Plots were harvested to a 5-cm stubble height
with a flail-type forage harvester (Carter Mfg., Brookston,
IN) equipped with an automated weigh system to determine
forage yield. To avoid border effect, a 1-m strip was harvested
from the middle of each plot. The unharvested forage from
the borders was mowed, raked, and removed to promote
even regrowth.
A random sample of forage was collected from each plot,
weighed, and dried for 48 h in a forced-air dryer at 60⬚C.
These samples were used to determine dry matter yield and
forage quality. Dried samples were ground to pass a 1-mm
mesh screen (Cyclone Mill, UDY Mfg., Fort Collins, CO).
Samples from each plot on each harvest date were analyzed
to determine concentrations of CP, IVDMD, and NDF by
near-infrared reflectance spectroscopy (Windham et al., 1989).
Fig. 1. Daily distribution of rainfall during April to September (A to
S) for legume–grass mixtures and legume and grass monocultures
grown near Boone, IA, in 1995 and 1996.
Reflectance measurements (log 1/R ) were collected for all
samples from 1100 to 2500 nm and recorded at 4-nm intervals
by using a Pacific Scientific 6250 scanning monochromator
(NIRS Systems, Silver Springs, MD). Based on spectral characteristics, a subset of 50 samples that represented the entire
range of H-values within the sample population was selected
for calibration (Shenk and Westerhaus, 1991a). Estimates
of CP and IVDMD were determined by micro-Kjeldahl
(Bremner and Breitenbeck, 1983) and two-stage IVDMD
(Marten and Barnes, 1980) procedures, respectively. Rumen
fluid was collected from a fistulated steer that was fed alfalfa.
The ANKOM 200 Fiber Analyzer (ANKOM Technology
Corp., Fairport, NY) was used to determine NDF as described
by Vogel et al. (1999). The NDF solution used was the ANKOM Fibersol-T solution. All analyses were performed twice,
and averages of the duplicates were used for statistical
analyses.
Legume composition of legume–grass mixtures was determined by using a modification of the constituent differential
method as described by Moore et al. (1990), in which NDF
and CP are used to estimate composition.
Calibration equations were developed with modified partial
least squares regression (Shenk and Westerhaus, 1991b). Coefficients of determination (R2) and standard errors of calibration and cross validation were, respectively, 0.97, 1.17, and
1.73 for IVDMD; 0.97, 1.52, and 1.93 for NDF; and 0.98, 0.48,
and 0.66 for CP. Calibration statistics were within acceptable
limits for the analytes (Windham et al., 1989).
Experimental Design and Statistical Analysis
The experimental design was a randomized complete block
in a split-split-plot arrangement with four replications. Whole
plots consisted of each legume and grass grown in monoculture
and in binary mixtures (a total of 15 treatments). Four harvest
dates represented the split-plot, and year was the split-split
plot. Statistical analysis of yield, quality, and legume composition data was performed with the General Linear Model procedure of SAS (SAS Inst., 1991). Mean comparisons were
made with an F-protected LSD (Steele and Torrie, 1980) at
P ⱕ 0.05 unless otherwise noted.
RESULTS
Yield
Yield differences occurred between years, and among
treatments and harvests (Table 1). Treatment–year and
treatment–harvest–year interactions also were observed.
Yields from the first harvest were the largest of the
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AGRONOMY JOURNAL, VOL. 92, JANUARY–FEBRUARY 2000
Table 1. Mean yield of smooth bromegrass, orchardgrass, intermediate wheatgrass, alfalfa, birdsfoot trefoil, and kura clover grown in
monoculture and in binary mixtures near Ames, IA, in 1995 and 1996. Grasses were fertilized with 67 kg N ha⫺1; mixtures were
not fertilized.
Yield
1995 harvests
Species
1
2
1996 harvests
3
4
Total
1
2
3
4
Total
kg dry matter ha⫺1
Grass monocultures
Smooth bromegrass (SB)
Orchardgrass (OG)
Intermediate wheatgrass (IW)
Legume monocultures
Birdsfoot trefoil (BFT)
Alfalfa (ALF)
Kura clover (KC)
Legume–grass mixtures
SB–BFT
SB–ALF
SB–KC
OG–BFT
OG–ALF
OG–KC
IW–BFT
IW–ALF
IW–KC
3065†
2390
2797
294
448
315
533
666
681
110
135
219
4 002
3 639
4 012
1260
1159
1216
142
428
500
250
322
347
227
343
493
1879
2252
2556
5385
5614
3945
2333
2913
1429
2675
3402
2631
203
1534
387
10 596
13 463
8 392
873
2441
1497
1069
1679
923
1416
2384
1164
409
1010
856
3767
7514
4440
6822
6742
5454
5093
5819
4448
5994
6849
5688
1722
2018
895
1735
2037
1305
1624
1976
976
1909
2668
2027
1922
2377
2210
1993
2653
2280
249
1186
419
563
980
491
389
1258
643
10 702
12 614
8 795
9 313
11 213
8 454
10 000
12 736
9 587
1357
2187
1679
1115
1651
1444
962
2188
1527
683
1068
866
526
1040
822
804
1265
933
1116
2367
1061
1347
1795
1323
788
2093
1252
464
1110
866
672
1120
1156
614
1227
1018
3620
6732
4472
3660
5606
4745
3168
6773
4730
† LSD (0.05) ⫽ 244. Appropriate for within and between harvest comparisons.
four harvests (Table 1). Alfalfa grown in monoculture
had higher total yield (146–356%) than birdsfoot trefoil
and kura clover in monoculture and all binary mixtures.
Alfalfa also had the lowest yield decline over the season
(67%). Greatest total yield was observed for alfalfa–
intermediate wheatgrass in 1995 and 1996. Alfalfa–
intermediate wheatgrass had greater yields than all
other mixtures at all harvests except Harvests 2 and 3
in 1995 and Harvest 3 in 1996.
Binary mixtures had 100% or higher yield than all
grasses in monoculture (Table 1). Alfalfa–grass mixtures
had the highest overall yield (Table 1). When averaged
over all harvests, alfalfa–grass mixtures had threefold
higher yield than smooth bromegrass, orchardgrass, and
intermediate wheatgrass grown in monoculture.
Inclusion of legumes improved cumulative yield. The
fourth harvest of alfalfa–smooth bromegrass was 10
times that of smooth bromegrass in monoculture (Table
1), which had the largest yield decline over the season,
with 96 and 81% in 1995 and 1996, respectively, compared with its first-harvest yield. Birdsfoot trefoil–
smooth bromegrass did not have yields or seasonal distribution of yield equal to that of alfalfa–smooth
bromegrass mixture. Alfalfa in monoculture had the
least yield decline throughout the season, followed by
kura clover and alfalfa–orchardgrass, respectively. A
91% decline in yield was observed over the season for
birdsfoot trefoil–smooth bromegrass. The yield decline
was larger for birdsfoot trefoil–smooth bromegrass than
for alfalfa–smooth bromegrass.
Table 2. Mean in vitro dry matter digestibility (IVDMD) of smooth bromegrass, orchardgrass, intermediate wheatgrass, alfalfa, birdsfoot
trefoil, and kura clover grown in monoculture and in binary mixtures near Ames, IA, in 1995 and 1996. Grasses were fertilized with
67 kg N ha⫺1; mixtures were not fertilized.
IVDMD
1995 harvests
Species
1
2
1996 harvests
3
4
g
Grass monocultures
Smooth bromegrass (SB)
Orchardgrass (OG)
Intermediate wheatgrass (IW)
Legume monocultures
Birdsfoot trefoil (BFT)
Alfalfa (ALF)
Kura clover (KC)
Legume–grass mixtures
SB–BFT
SB–ALF
SB–KC
OG–BFT
OG–ALF
OG–KC
IW–BFT
IW–ALF
IW–KC
kg⫺1
1
2
3
4
dry matter
592†
554
579
549
603
571
575
563
570
525
558
551
708
706
704
667
613
663
654
647
656
609
655
654
621
627
751
671
688
769
648
639
729
556
665
712
732
703
804
717
689
777
706
679
776
681
732
784
621
606
684
618
619
702
617
621
681
678
692
718
661
668
721
689
694
734
602
637
708
619
635
708
631
619
718
609
689
705
626
654
696
599
683
692
689
710
786
700
705
794
702
704
789
697
707
761
675
690
758
697
709
766
697
674
748
681
710
760
690
681
770
717
734
777
724
735
770
681
745
768
† LSD (0.05) ⫽ 17.8. Appropriate for within and between harvest comparisons.
27
SLEUGH ET AL.: BINARY LEGUME–GRASS MIXTURES IMPROVE FORAGE YIELD
Table 3. Mean crude protein (CP) of smooth bromegrass, orchardgrass, intermediate wheatgrass, alfalfa, birdsfoot trefoil, and kura
clover grown in monoculture and in binary mixtures near Ames, IA, in 1995 and 1996. Grasses were fertilized with 67 kg N ha⫺1;
mixtures were not fertilized.
CP
1995 harvests
Species
1
2
1996 harvests
3
4
1
2
3
4
g kg⫺1 dry matter
Grass monocultures
Smooth bromegrass (SB)
Orchardgrass (OG)
Intermediate wheatgrass (IW)
Legume monocultures
Birdsfoot trefoil (BFT)
Alfalfa (ALF)
Kura clover (KC)
Legume–grass mixtures
SB–BFT
SB–ALF
SB–KC
OG–BFT
OG–ALF
OG–KC
IW–BFT
IW–ALF
IW–KC
85†
93
93
133
130
133
139
123
131
120
118
128
161
156
175
161
139
159
160
158
169
113
114
141
183
171
174
210
200
213
149
184
194
163
213
196
228
220
234
194
178
205
182
185
209
164
210
187
130
134
130
139
141
143
153
140
139
197
192
195
182
183
184
204
197
198
190
193
200
173
189
181
177
195
191
162
207
183
153
187
177
155
204
182
179
220
217
196
213
214
191
216
216
193
185
205
176
182
198
182
191
207
188
180
207
176
191
195
186
189
211
171
211
192
175
187
174
161
221
184
† LSD (0.05) ⫽ 10. Appropriate for within and between harvest comparisons.
Overall yields decreased in 1996. The most significant
decreases (65% on average) were observed for birdsfoot
trefoil and birdsfoot trefoil–grass mixtures. Alfalfa and
alfalfa–grass mixtures, and kura clover and kura clover–
grass mixtures had an average decrease of 47 and 56%,
respectively (data not shown).
est average CP. Kura clover and all kura clover–grass
mixtures consistently had CP equal to or higher than
birdsfoot trefoil and alfalfa grown in monoculture.
Crude protein of kura clover–smooth bromegrass, kura
In Vitro Dry Matter Digestibility
Binary mixtures had higher IVDMD than grass monocultures (Table 2). Fluctuations in IVDMD were evident throughout the season, primarily in monocultures.
Averaged over harvests, IVDMD levels separated
into four groupings, within which treatments did not
differ. Kura clover had the greatest IVDMD, followed
by kura clover–grass mixtures, alfalfa–grass, and birdsfoot trefoil–grass mixtures, with the three grass monocultures having the lowest IVDMD (Table 2).
Grass monocultures had lower IVDMD at the fourth
harvest compared with the first harvest (Table 2). Except for kura clover–orchardgrass, birdsfoot trefoil–
intermediate wheatgrass, and kura clover–intermediate
wheatgrass, all legume–grass mixtures had higher
IVDMD at Harvest 4 than at Harvest 1. The highest
IVDMD for kura clover was at Harvest 1; the other
harvests did not differ. For alfalfa, digestibility at Harvests 1 and 3 was similar, but digestibility increased at
Harvest 4.
Crude Protein
Grass monocultures had lower CP than legume monocultures and legume–grass mixtures (Table 3). Crude
protein concentrations of birdsfoot trefoil–smooth
bromegrass, alfalfa–smooth bromegrass, and kura clover–smooth bromegrass mixtures were 31, 46, and 46%
higher, respectively, than that of the smooth bromegrass monoculture.
Of legumes in monoculture, kura clover had the high-
Fig. 2. Seasonal variation of legume species composition for birdsfoot
trefoil, alfalfa, and kura clover, each in binary mixtures with (a )
orchardgrass, (b ) smooth bromegrass, and (c ) intermediate wheatgrass. Data are averaged over 2 yr.
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AGRONOMY JOURNAL, VOL. 92, JANUARY–FEBRUARY 2000
Table 4. Mean neutral–detergent fiber (NDF) of smooth bromegrass, orchardgrass, intermediate wheatgrass, alfalfa, birdsfoot trefoil,
and kura clover grown in monoculture and in binary mixtures near Ames, IA, in 1995 and 1996. Grasses were fertilized with 67 kg
N ha⫺1; mixtures were not fertilized.
NDF
1995 harvests
Species
1
2
1996 harvests
3
4
1
2
3
4
g kg⫺1 dry matter
Grass monocultures
Smooth bromegrass (SB)
Orchardgrass (OG)
Intermediate wheatgrass (IW)
Legume monocultures
Birdsfoot trefoil (BFT)
Alfalfa (ALF)
Kura clover (KC)
Legume–grass mixtures
SB–BFT
SB–ALF
SB–KC
OG–BFT
OG–ALF
OG–KC
IW–BFT
IW–ALF
IW–KC
598†
587
617
567
565
557
580
587
585
554
540
558
548
524
511
472
523
473
494
496
481
527
480
488
472
459
379
419
406
356
534
508
429
523
361
356
365
406
325
379
399
342
417
405
338
426
347
329
569
564
500
557
554
472
540
571
520
459
430
437
494
482
439
424
418
409
521
496
438
543
511
460
527
517
446
463
375
378
468
419
388
515
393
399
478
423
358
436
424
356
439
417
365
415
382
369
456
424
391
422
385
369
441
414
376
452
415
388
445
418
368
407
355
344
387
367
359
461
337
362
† LSD (0.05) ⫽ 21. Appropriate for within and between harvest comparisons.
clover–orchardgrass, alfalfa–smooth bromegrass, and
alfalfa–orchardgrass were similar.
Generally, CP increased after the first harvest (Table
3) in legume–grass mixtures; this may have been due
to the increase in the percent legume in the mixtures
(Fig. 2).
Neutral-Detergent Fiber
Legumes in monoculture or in binary mixtures with
grasses had lower NDF than grasses grown in monoculture (Table 4). The kura clover monoculture had the
lowest NDF, followed by kura clover–orchardgrass and
kura clover–smooth bromegrass, respectively. Alfalfa
NDF was higher than those of kura clover and the three
kura clover–grass mixtures. Overall, alfalfa and alfalfa–
grass mixtures had lower NDF values than birdsfoot
trefoil and its mixtures. Alfalfa–smooth bromegrass had
the lowest NDF of all alfalfa mixtures, followed by alfalfa–intermediate wheatgrass and alfalfa–orchardgrass,
respectively. On average, the first three harvests of all
species had greater NDF concentrations than the fourth
harvest. Neutral-detergent fiber concentrations in 1996
were lower than those in 1995 (data not shown). The
largest reduction (30%) was observed for kura clover–
intermediate wheatgrass.
DISCUSSION
Including legumes with grasses improved yield distribution throughout the season (Table 1). The observed
improved distribution in yield may be caused by differences in growth legume composition at different times
throughout the season (Fig. 2). Except for orchardgrass–
alfalfa, the percentage of legumes increased for smooth
bromegrass and orchardgrass mixtures after the second
and third harvest. Of the intermediate wheatgrass mixtures, only alfalfa–intermediate wheatgrass showed a
consistent increase in the percentage of legumes (Fig.
2). Kura clover and birdsfoot trefoil was not as vigorous
as alfalfa was in the intermediate wheatgrass mixtures.
Alfalfa and alfalfa–grass mixtures, which probably
produced greater yields because the deep root system
of alfalfa plants was able to tap deeper soil water, had
larger fourth-harvest yield than kura clover and birdsfoot trefoil monocultures or their binary mixtures (Table 1). Therefore, for alfalfa and alfalfa–grass mixtures,
a fourth harvest may be optional in central Iowa and
will depend on whether yield, quality, or persistence is
the main priority of the producer. Yields from the fourth
harvest may have been lower because of slow recovery
after the third harvest in August. Approximately 88%
of the cumulative yield over the four harvests was obtained in the first three harvests. There was a large
reduction in yield from 1995 to 1996 for all legume
species and their mixtures (Table 1). The yield decrease
may be explained by a cool, wet spring (Fig. 1) and an
unseasonably cool late summer in 1996. Our observations suggest that yield reduction in monoculture birdsfoot trefoil and birdsfoot trefoil–grass mixtures was because of a significant visible reduction in the vigor and
amount of birdsfoot trefoil in these plots and an invasion
of weeds, mostly Canada thistle [Cirsium arvense (L.)
Scop.]. An overall decline in the percentage legume was
observed mostly between the second and third harvest
in 1996 compared with 1995.
Consistent with the results of Allinson et al. (1985)
and Sheaffer and Marten (1991), kura clover and its
mixtures consistently had higher IVDMD than other
legumes and their mixtures (Table 2). At each harvest,
we observed that kura clover (late vegetative) was usually not as mature as alfalfa (early bloom), and this
maturity status may have contributed to the increased
IVDMD. The concentrations of IVDMD (Table 2) and
CP (Table 3) were increased, and NDF (Table 4) was
decreased in 1996 compared with 1995. Reduced forage
growth in 1996 may be correlated with the increase
SLEUGH ET AL.: BINARY LEGUME–GRASS MIXTURES IMPROVE FORAGE YIELD
of IVDMD and CP and the decrease in NDF. This
observation agrees with that of Van Soest (1982), who
reported that when environmental stresses slow plant
growth and development, forage quality will be maintained for a longer period of time. Our results showed
that kura clover was similar to alfalfa and alfalfa–grass
mixtures in CP concentration. These results are consistent with those of Allinson et al. (1985), Sheaffer and
Marten (1991), and Posler et al. (1993), who reported
that increases in IVDMD and CP resulted when legumes, especially kura clover, were included with
grasses.
Our results suggest that including legumes with
grasses can improve IVDMD, CP, NDF, and seasonal
distribution of forage yield. The improved seasonal distribution was especially evident in alfalfa–grass mixtures, which showed higher yields in the fourth harvest
than kura clover and birdsfoot trefoil in monoculture or
in their mixtures with smooth bromegrass, orchardgrass,
and intermediate wheatgrass. However, the significant
increase in legume composition in legume–grass mixtures over the season suggests that the grasses were not
as persistent or vigorous under our four-cut system. On
average, the legume percentage was higher in smooth
bromegrass mixtures than in orchardgrass and intermediate wheatgrass mixtures after the third harvest.
Alfalfa–intermediate wheatgrass yields were equal to
or greater than other alfalfa–grass mixtures at each harvest, indicating that this binary mixture could be a good
alternative to more common mixtures such as alfalfa–
orchardgrass or alfalfa–smooth bromegrass. The hardiness of intermediate wheatgrass in this mixture was evident, as it maintained high yields even at a time when
other cool-season grasses were dormant or had less
growth.
The improved crude protein level of the legume–grass
mixtures could reduce the amount of supplements fed
by livestock producers, because they would have more
high-quality forage distributed over the season. If legume–grass mixtures are used for hay, the increased
yields per unit area could supply higher quality forage
for livestock and reduce the amount of land needed to
produce the required forage.
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