Table 1 Percentage Italian ryegrass plant cover relative to total plant cover for each plot type, measured 141 days after wheat sowing
a
Pure I. Ryegrass Barnyardgrass
Mixed wheat-I. Ryegrass Hedges
Low density High density
High density Low density
Total Relative
Total Relative
Relative Total
Relative Total
Yes 100.0
11.8 100.0
0.8 15.7
44.0 4.2
37.9 No
100.0 31.2
100.0 3.5
46.3 39.6
33.8 33.0
a
Within each column of values, denotes a significant PB0.05 difference between barnyardgrass and non-barnyardgrass plot means.
In this study, we tested the hypothesis that manipulating some agronomic variables, aiming
to produce changes especially in the light environ- ment during early stages of the crop, can improve
wheat ability to compete with ryegrass. Live and dead hedges grown with summer annuals barn-
yardgrass and maize, separated by various dis- tances, were used to reduce the ground-level light
intensity and alter the R:FR ratio during winter wheat seedling establishment in Italian ryegrass
infested plots.
2. Materials and methods
2
.
1
. Experiment
1
A factorial experiment was established to deter- mine the effect of short-term shading, using barn-
yardgrass Echinochloa cruss-galli hedges, on wheat Triticum aesti6um and Italian ryegrass
biomass production. A split-split plot experimen- tal design with three replications was used. High
or low-density Italian ryegrass seed banks were
Table 2 Vegetative and reproductive biomass of wheat and Italian ryegrass grown in pure stands and mixed plots, at high or low Italian
ryegrass seed bank density and harvested from 0.04 m
2
sampling plots at the end of the growing cycle
a
Species Wheat
Italian ryegrass seed bank density Barnyard
grass Low
High Low
Hedges High
Reproductive biomass g Vegetative biomass g
65 72
Yes 60
61 No
36 43
45 42
Ryegrass Pure stand
Pure stand Mixed stand
Mixed stand Pure stand
Mixed stand Pure stand
Mixed stand Reproductive biomass g
Vegetative biomass g 6
6 Yes
9 16
3 5
5 8
No 10
19 17
10 3
4 8
15
a
Within each column of values, denotes a significant PB0.05 difference between barnyardgrass and non-barnyardgrass plot means.
Table 3 The effect of live green and dead brown hedges on the light microenvironment at ground level on the South side of hedges
oriented E–W. Values represent mean quantum flux mmol m
− 2
s
− 1
Distance from hedge Facing the sky
Facing the hedge Hedge type
m 660 nm
730 nm R:RL
660 nm 730 nm
R:RL 179.8 4.34
a
169.4 6.2 1.04 0.01
3.3 1.9 Green
16.7 2.6 0.0
0.20 0.08 175.4 4.37
161 1.66 1.06 0.02
0.6 5.9 1.4
21.9 6.2 0.26 0.03
1.2 176.5 6.53
158.7 7.99 1.10 0.01
8.4 0.79 23.5 1.8
0.36 0.05 0.0
Brown 180.1 3.2
a
173.2 4.0 1.01 0.01
6.2 1.3 27.7 0.8
1.03 0.02 176.3 4.6
167.9 2.3 0.95 0.03
0.6 19.8 2.2
28.2 2.1 1.01 0.01
1.2 172.4 2.6
158.2 5.4 1.07 0.02
20.1 1.4 27.3 3.0
1.11 0.04
a
S.D. n = 3
main plots while presence or absence of barnyard- grass hedges were the sub-plots and the presence
or absence of winter wheat were the sub-subplots. The experiment was conducted at the Oregon
State University Vegetable Research Farm, De- partment of Horticulture, in Corvallis, Oregon
during the 1989 – 1990 growing season. The exper- imental site contained soil from the Chehalis se-
ries, a silty clay loam with 7 organic matter and a pH of 6. In late September, 1 year before the
experiment began, high- and low-density Italian ryegrass seed banks were established in the fol-
lowing manner: three 4 m
2
plots were planted with Italian ryegrass seed only pure stand, and
three other plots were planted with a mixture of Italian ryegrass and winter wheat. Since wheat
competition reduced Italian ryegrass seed produc- tion in the mixed plots, the resulting Italian rye-
grass seed banks were different in the mixed and pure plots. Measurements taken during the fol-
lowing summer revealed that the seed bank in pure stands averaged 170 000 Italian ryegrass
seeds m
− 2
while in the mixed plots, weed density averaged 39 000 ryegrass seeds m
− 2
. On 22 August, soil in all the experimental plots
was rototilled and half of each plot was trans- planted with barnyardgrass in rows 0.5 m apart
and oriented in an East – West E – W direction Fig. 1. Within each row, plants were spaced at
0.1 m apart, and generated a hedge approximately 0.5 m high at the time of transplanting. Soil in the
other half of each plot was also disturbed with a transplant shovel but did not receive barnyard-
grass transplants. On 7 October, the bare soil between the barnyardgrass hedges, and all the soil
in the unplanted half of each plot, was again disturbed with a shovel and fertilized with 15 –
15 – 15 NPK 10
3
kg ha
− 1
and irrigated. The next day, the plots were subdivided in North –
South N – S direction and wheat was sown in one half of each plot in rows 0.125 m apart. Thus,
each main plot contained two sub-plots barn- yardgrass hedges or bare soil and two sub-sub-
plots with and without wheat Fig. 1. Sowing was accomplished by opening small furrows with
a rake, distributing the seed 350 seeds m
− 2
, and raking the furrows closed.
By the first week of November, all the barn- yardgrass plants had died and these plants and
any Italian ryegrass plants that had been growing within hedgerows were removed. In the last week
of February, specific cover in 0.5 m by 0.2 m sampling areas was determined in all treatments
sub-sub plots. For this purpose we used a cross- wire sighting device similar to that described by
Beaumer and de Wit 1968 to register presence or absence of a species’ leaves at each of 50 sample
points per plot. On 9 July aboveground biomass in 0.1 m by 0.4 m sampling areas was harvested
from all the treatments and separated into vegeta- tive and reproductive matter.
2
.
2
. Experiment
2
A split – split plot experimental design with three replicates was used to study the effects of
orientation and spacing of live green and dead brown maize hedges on interference between
wheat and Italian ryegrass. In this case, the main plots were hedgerow orientation N – S or E – W,
while subplots were live or dead hedges, which created different light environments Ballare´ et al.,
1987. Sub-subplots were hedge spacing 1.2, 2.4, 3.6, 4.8, and 6.0 m Fig. 2.
The experiments were conducted at the Oregon State University Hyslop Field Laboratory near
Corvallis, Oregon, during two growing seasons: 19891990 and 19901991. Soil was an Amity silt
loam with a pH of 5.2 and containing 2.6 organic matter. A 2-ha site heavily infested with
Italian ryegrass was plowed at the end of March both years and again on 25 June. It was then
Fig. 3. Red:Far red 650 nm:730 nm quantum flux ratio of the light reaching the soil at increasing distances from the unsprayed maize hedge oriented N – S and E – W
when hedges were separated 1.2 m a, 2.4 m b, 3.6 m c, 4.8 m d or 6.0 m e.
Measurements were taken at midday on a sunny day. Global fluence rate was 1200 mmol m
− 2
s
− 1
.
Table 4 Correlations of environmental and yield variables with the first
three axis from principal component analysis
a
Variable Axis 3
Axis 2 Axis 1
eig = 0.09 eig = 0.23
eig = 0.64 −
0.312 WTVEG
0.413 −
0.855
− 0.136
WTREP −
0.341 −
0.926
− 0.304
−
0.839 −
0.166 WTSPK
RYEVEG 0.568
−
0.815 −
0.085 −
0.644 0.482
0.064 RYEREP
−
0.683 RYESPK
− 0.143
0.657 −
0.490 0.084
− 0.354
ORIENT 0.110
COLOR −
0.070 −
0.119 −
0.289 −
0.169 0.078
DISTAN
a
Eigenvalues eig given for each axis represent the variance in the matrix attributed to that axis. WTVEG: wheat vegeta-
tive weight; WTREP: wheat reproductive weight; WTSPK: number of wheat spikes; RYEVEG: ryegrass vegetative
weight; RYEREP: ryegrass reproductive weight; RYESPK: number of ryegrass spikes; ORIENT: orientation of hedges
N–S or E–W; COLOR: color of hedges after spraying green or brown; DISTAN: distance between two hedges.
sprayed with 0.5 kg a.i. paraquat 1-1-dimethyl- 4, 4-bipyridinium ion Fig. 2, to kill the
treated maize plants and create different light environments sub-plots.
The spacing sub-subplots of 1.2, 2.4, 3.6, 4.8 or 6.0 m between the maize hedges were created
with a 1.2-m wide rototiller. Four tilling opera- tions carried the first week of September were
necessary to destroy the maize plants between the hedges and prepare the soil for later wheat
planting. On 28 September and 1 October, re- spectively, wheat was sown with an eight-row
planter at a rate of 350 seeds m
− 2
. To characterize differences in light quality at
ground level in the different hedge spacing and orientations existing before sowing wheat, R:FR
determinations were taken at increasing dis- tances
from sprayed
and unsprayed
maize hedges every 0.6 m. Measurements were done at
midday on a sunny day, with a Skye Radiome- ter model SKR 100, and a sensor model SKR
110. Reductions in light intensity caused by live and dead fences were quantified by comparing
quantum flux at 660 and 730 nm when the sen- sor was facing the sky and when it faced the
hedge. For this purpose, we measured light in- tensity on the South side of the fences oriented
E – W at 0, 0.6 and 1.2 m from the fence. Maize plants were around 1.50 m high and were start-
ing to tassel.
Between 22 June and 10 July, aerial biomass was sampled in all sub-subplots. To do the sam-
plings, 1.0 m by 1.0 m quadrats were located along a line transect in both the sprayed and
unsprayed halves of each main plot. Transects ran perpendicular to the maize hedges and had
their origins positioned randomly within each plot half Fig. 2B. Within each spacing between
the maize hedges, the first quadrat was located 0.1 m from the preceding maize hedge, the next
quadrat, if row spacing allowed more than one was located 0.2 m from the preceding quadrat.
In this way, samples from one, two, three, four, or five quadrats, depending on whether the
quadrats were from the 1.2, 2.4, 3.6, 4.8 or 6.0 hedge spacing, were obtained for each treat-
ment. Vegetative and reproductive dry biomass was recorded by species ryegrass and wheat.
tilled with a disc harrow and fertilized with 16 – 20 – 0 NPK 2.5 × 10
3
kg ha
− 1
. On 19 and 21 July, respectively each year, the
site was tilled again and planted with maize 70 kg seed ha
− 1
, in rows 0.6 m apart. The rows were oriented N – S in half of each block and
E – W in the other half Fig. 2A to create the two main plots.
To create a homogeneous Italian ryegrass stand in the plots, 17 kg Italian ryegrass seed
ha
− 1
was broadcast in the established maize during the last week of August. The experiment
was irrigated as needed. On 26 September, half of the maize hedges in each main plot were
Table 5 Climatic conditions during wheat and ryegrass seedling growth
Mean daily Month
Monthly precipation temperature °C
mm 1990
1989 1990
1989 18.1
43.7 20.0
August 22.1
17.9 18.4
September 15.2
21.1 11.4
115.8 October
67.6 10.7
123.7 99.1
7.8 November
7.9 4.2
December 1.0
78.0 89.9
Fig. 4. Effect of maize hedge spacing on vegetative and reproductive wheat biomass for maize hedges oriented E – W and N – S A and live and dead maize hedges B.
Fig. 5. Effect of maize hedge spacing on vegetative and reproductive Italian ryegrass biomass for maize hedges oriented E – W and N – S A and live and dead hedges B.
Fig. 6. Ryegrass biomass as a function of wheat biomass in 1 m
2
plots with green alive or brown dead maize hedges oriented E – W or N – S. Regression models are: green hedges,
E – W: y = − 0.0027x + 6.379
R
2
= 0.26;
N – S: y = −
0.0001x + 3.9895 R
2
= 0.00; brown hedges, E – W: y = −
0.003x + 6.157 R
2
= 0.30;
N – S y = − 0.0018x + 5.0874
R
2
= 0.09.
5 level of significance. Linear regressions were calculated for the logarithm of the biomass of
each species against the biomass of the other one, and number of spikes or reproductive biomass
versus vegetative biomass for each species.
In order to account for the competitive effect of the maize row, we compared regression curves
obtained with the whole data set versus those obtained only with subsamples taken at least 1.2
away from the maize row, in the hedge spacings of 3.6, 4.8 and 6.0 m.
Fig. 7. Wheat biomass as a function of ryegrass biomass in 1 m
2
plots with green alive or brown dead maize hedges oriented E – W or N – S. Regression models are: green hedges,
E – W: y = − 0.0014x + 6.7421
R
2
= 0.21;
N – S: y = −
0.0002x + 6.4663 R
2
= 0.00; brown hedges, E – W: y = −
0.0013x + 6.6566 R
2
= 0.23;
N – S y = − 0.001x + 6.7586
R
2
= 0.11.
2
.
3
. Data analysis Differences in cover and biomass among treat-
ments of the first experiment were analyzed using analysis of variance P B 0.05. We used Principal
Components Analysis PCA and Pearson and Kendall correlations on variable means to identify
the most important factors determining the crop and weed responses in the second experiment
Digby and Kempton, 1991. We used a two-way analysis of variance ANOVA, and tested for the
effects of hedge spraying and orientation, and the interactions with spacings. Treatment means were
separated by Fisher’s Protected LSD test at the
Fig. 8. The relationship between reproductive and vegetative biomass in wheat plants growing in 1 m
2
plots with green alive or brown dead maize hedges oriented E – W or N – S.
Regression models are: green hedges, E – W: y = 0.5918 + 65.705
R
2
= 0.82;
N – S: y = 0.6723x + 91.858
R
2
= 0.67;
brown hedges, E – W: y = 0.5398x + 146.88 R
2
= 0.42; N – S
y = 0.5996x + 67.746 R
2
= 0.69.
tively, in high and low-density plots Table 1 by the presence of barnyardgrass hedges.
Response to the barnyardgrass hedges was also evident in aboveground biomass production at the
end of the crop cycle. Overall the hedge signifi- cantly improved wheat vegetative and reproduc-
tive biomass, in both the high and low Italian ryegrass seed bank density treatments Table 2.
In all the treatments high and low Italian rye- grass seed bank density, pure and mixed stands
barnyardgrass hedges reduced Italian ryegrass vegetative yield compared to the non-hedge areas,
but the hedges did not significantly affect repro- ductive yield of Italian ryegrass Table 2.
Fig. 9. The relationship between reproductive and vegetative biomass in ryegrass plants growing in 1 m
2
plots with green alive or brown dead maize hedges oriented E – W or N – S.
Regression models are: green hedges, E – W: y = 0.3433x + 1.962 R
2
= 0.58; N – S: y = 0.1008x + 1.1774 R
2
= 0.76; brown
hedges, E – W: y = 0.2618x + 6.8231 R
2
= 0.59; N – S y =
0.1351x + 1.6479 R
2
= 0.87.
3. Results and discussion
