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8/9/2019 Row Cover & Population Density Effects on Yield of Bell Peppers in South Coastal British Columbia; Gardening Guidebook
1/9
Row
cover and
population
density
effects
on
yield
of
bell
peppers
in south
coastal
British
Columbia
M.
M. Gaye1,
P. A.
Jolliffe2,
and
A.
R.
Maurer3
I
Cloverdale
Soil Conservation
Group,
17720-57th
Ave., Surrey,
British
Columbia,
Canada
VJS
4P9;2
Department of Plant
Science, 'tJniversity
of
British
Columbia,
Vancouver,
British
Columbia,
Caiada
V6T 124;
and3Agriculture
Canada
Research
Station,
Agassiz,
British
columbia, canadav)M
1A0. Received
26
April
1991,
accepted
ZS
March 1992.
Gaye,
M.
M.,
Jolliffe,
P.
A.
and
Maurer,
A.
R. 1992.
Rolv cover
and
population density
effects
on
yield
of bell
peppers
in south
coastal
British
Columbia.
Can.
J.
Plant Sci.
72: 901-909.
Row
covLr and
plant
population
density
effects
were
studied
at the Agriculture
Canada
Research
Station,
Agassiz,
gC
in tgSS
and 1989.
Bell
pepper
plants
(Ace
Hybrid)
were transplanted
into twin
rows
(0.45
m
upi.t)onraisedbeds(1.8-mcenters)atfivepopulationdensitiesof
1.39,
1.85,2.78,5.56and
lf
i
plant
*
'.
Fo.7
wk in 1988 or 8
wk in 1989,
iubplots
were either
covered
or not
covered
with
slit
clear
polyethylene
tunnels.
A nonlinear
regression
model
was used to define
yield-population density
responses.
Row
covers enhanced
early
and
overall
yiekis
in
1988 and
overall
yield
in
1989. Vegetative
and
reproductive
yields
(kg
plani-r;
declined
with
increasing
plant population
density.
Yields
were.directf
reiated to
population
density
when
measured
on
a
land-area
basis.
Maximum
fruit
yield
(7.9
kg
m
')
was obtained at the highest
population density.
Treatment
influences
on
fiuit size
were small
and
did
not affect horticulturafqualiiy.
An economic
analysis
showed
that
net
returns
were
greatest
with
plants
grown
under row covers
at the highest
population density.
Key
words:
capsicum
annuum
L.,
field
bell
peppers,
population
density,
row covers
Gaye,
M. M.,
Jolliffe,
P. A.
et Maurer,
A.
R. 1992.
Effets d'une
couverture
plastique
et
de la den-
siti de
peuplement
sur
le rendement
du
piment
cloche
dans
la
zone c0tibre
du
sud
de
la
Colombie-
Britanniqul. Can. J.
Plant
Sci.
72:901-909.
Les
effets de
la couverture
plastique
et
de
la densit6
de
peuplement ont
6t6
6tudi6s
ir
la
station f6d6rale
de
recherches
agronomiques
d'Agassiz
(C.-B.)
en
t988 et
1989. Des
plants
de
piment cloche
(Ace
hybrid)
ont
6t6
repiqu6s
sur billons
(1,8
m centre
it
centre) en
lignes
jumel6es
(6iarteement
de
0,45
m), d 5
densit6s
de
peuplement
:
1,39, 1,85'
2,78'
5,56 et
1l,l
plantes
au
mbtre carr6.
Pendant
7 semaines
en
1988 et
huit semaines
en 1989,
des sous-
parcelles
dtaient soit
recouvertes
ou non
recouvertes
de
mini-tunnels
de
poly6thylene
transparenf
per-
ior6.
Un
modble
de
r6gression
non lin6aire
a 6t6
utilis6
pour
d6finer
les r6ponses
rendement-densit6
de
peuplement.
Les
mini-tunnels ont
augment6
le
rendement
pr6coce et
le rendement
total
en 1988
ainii
que
le rendement
total
en
1989.
L; rendement
v6g6tatiftet
fruitier
(kg
plante
r;
diminuait
en
proportion
de
I'accroissement
de la densit6.
Calculd
par unit6 de
surface,
le rendement
6tait
directe-
ment
li6
)r la
densit6.
Le rendement
le
plus
6lev6
(7,9
kg
-
';
6tait
obtenu
ir la densit6
la
plus
fofte.
Les
traitements
n'avaient
que
peu
d'effet
sur
le
calibre
des
fruits
et
n'influaient
pas
sur
leur
qualit6
horticole.
L'analyse 6conomique
a d6montr6
que
les
recettes
nettes
les
plus fortes
etaient obtenues
en
culture sous
mini-tunnel
d la
plus forte densit6
de
peuplement.
Mots cl6s: Capsicum
annuum L.,
piment
cloche
de
plein
champ,
densit6
de
peuplement,
mini-tunnel
plasrlque
Can.
J.
Plant Sci.
72: 90f-909
(July
f992)
901
p
y
8/9/2019 Row Cover & Population Density Effects on Yield of Bell Peppers in South Coastal British Columbia; Gardening Guidebook
2/9
902
CANADIAN
JOURNAL
OF PLANT SCIENCE
Field
production
of
bell
peppers
(Capsicum
annuum
L.) in
south
coastal British
Columbia
is
limited
because
of
the restricted
number
of
degree
days
above
10'C from
April
to
Sep-
tember
(851
degree
days)
(Environment
Canada
1982).
Transplants
are
used in
com-
mercial
production
to
promote
early
fruit
har-
vesting
and improve yields.
Row
covers
can also
be
used to
enhance
bell
pepper
fruit yield (Mohd
Khir
et al.
1981),
but
few Fraser
Valley
producers
have
adopted
this technique
because
of
the additional
costs.
Row
covers
could
become
economically
viable
if more productive
cropping
systems
were
developed.
Fraser
Valley
producers
cur-
rently plant
bell peppers,
such
as
Ace
Hybrid,
at
a within-row
spacing
of
0.30-0.40
m and
0.75-0.90
m between
rows
(British
Columbia
Ministry
of
Agriculture
and
Fisheries
(BCMAF)
1989).
These
recommendations
are
based
on
traditional
practices,
as
population
density
studies
have
not
been conducted
in
British
Columbia
(M.
Sweeney
1990,
BCMAFF,
personal
communication).
In
other
regions,
increasing
plant
population
density
has
resulted
in
greater
yields
of bell pepper
fruit
(Porter
and
Etzel
1982:
Ahmed
1984).
High population
densities
have
not
affected
fruit
size
(Stoffella
and Bryan
1988),
but
might
not
cause
yield
improvement
because
of
asymptotic
(Batal
and
Smittle
l98l)
or
parabolic
(Holliday
1960)
yield
density
responses.
Most row
cover
or
population
density
studies
of bell peppers
have
reported
fruit
yields
and
have not
considered
the
responses
of
vegetative
plant
components.
Monoculture
yield
density
responses
are
successfully
described
by reciprocal
equations
(Willey
and
Heath
1969),
such
as
Bleasdale's
0967)
model.
The
objectives
of our
studies were to
determine
the
effects
of row
covers
and plant
population
density
on
vegetative
and
reproductive
yields
of
bell
peppers
grown
in
south
coastal
Bntish
Columbia,
and to
deter-
mine
the economic
viability
of
the treatments.
MATERIALS
AND
METHODS
Studies
were
conducred
in
1988
and
1989 at the
Agriculture
Canada
Research
Station,
Agassiz,
British
Columbia.
Seven-week-old
bell
pepper
plants
(Ace
Hybrid,
Stokes
Seeds Ltd.,
Sr.
Catharines,
ON)
were
transplanted on
l2
May
in
both
years,
onto raised
beds mulched
with
black
polyethylene (thickness
28
pm).
The raised
beds
were
0.23
m
high, 1.1m
wide and
1.8 m
centre-to-centre.
The plants
were
transplanted
into
twin
rows
with
a
0.5-m
between-row
spacing. The
soil
(Rego
Humic
Gleysol,
pH
6.2)
had
been
prepared
in 1988 with
a
broadcast-
incorporated
application
of
165
N,
165 P2O5,
165 K2O
and 4.5 B
(kg
ha-',
respectively)
and with
23
t ha-' cattle manure.
In 1989,
the fertilizer
was
applied through
a trickle
irrigation
system
located under
the
plastic
surface
mulch.
The
experimental
design was
a split-plot with
four replications.
Main plots
were uncovered
or
were
covered
with slit
clear
polyethylene
tunnels
(thickness
50
pm).
Five
population
densities, 1.39,
1.85,
2.78,5.56
and
11.1plant
m-'
lcor-
responding
to
within-row
spacings of 0.8,0.6,
0.4,
0.2 and 0.1 m, respectively)
formed
the subplots.
Each
subplot consisted
of eight
plants;
the
plants
at the
end of
each row
were guards.
Row
covers
were
applied to
the
appropriate
treatments
immedi-
ately following
transplanting,
and
were removed
on
7 July 1988 and
14 July 1989.
Irrigation
(over-
head in
1988
and trickle in
1989) and
pesticides
(
ior
aphids)
were
applied as
necessary
throughout
the
growing
seasons.
Fruit
were
harvested
at the mature green
stage,
twice
a
week
from
3
Aug.
1988
and 19
July
1989,
until 21
Sept.
in
both
years.
The
harvested
fruit
were
graded
as marketable
(=
80
g
and
free
from
disease and insect
damage),
undersized
(
< 80
g)
,
or cull
(diseased
or insect
damaged),
and the
weight,
width
and length were recorded.
Fruit from
the initial
28 d of harvest were
considered
early
and
"overall
fruit
yield"
was rhe cumulative
yield
over the
entire harvest
period.
Two randomly
selected
plants
from each
plot
were
destructively harvested
on27 and 28
Sept.
1988. Plants
were removed
from the soil.
and the
roots
washed to remove
soil
particles.
Plant com-
ponents
(leaves,
stem
and
petioles,
and
roots)
were
oven-dried
to a constant
mass
at 70"C, and
the dry
masses
were recorded.
Air
temperatures
were monitored
30 cm above
the soil
surface with
thermisror
probes
(107,
Camp-
bell
Scientific, Logan,
UT)
and
a datalogging
microprocessor (21X,
Campbell
Scientific).
Daily
minimum
and maximum
temperatures and mean
hourly
temperatures,
each based
on readings
made
every 10 min, were
computed.
p
y
8/9/2019 Row Cover & Population Density Effects on Yield of Bell Peppers in South Coastal British Columbia; Gardening Guidebook
3/9
GAYE
ET
AL,
ROW COVER
AND
DENSITY
EFFECTS
ON BELL
PEPPERS
0.75
903
1.00
c\i
o
E
o)
J
Fj
T
l.,J
=
z
)
o_
trl
aF
-F
--u
(9
tJ
0.15
c')
Fj
-
Lr.,l
=
z
J
o_
LrJ
=
TJ
t
0.
r0
0.05
u.1f,
0.00
0.00
POPULATION
DENSITY,
Plonfs
m-'
Fig. 1.
Means and
nonlinear regressions
of 1988
vegetative
plant
dry
weight
on
population
density
for
uncovered.
-,(v
rEI
:
8.37
+ 17.1X,
RSS
:
0.025,
EMS
:
0.0007)'
and
covered,
-----
0
262
-
-95:7
+ 1r6X,
RSS
:
0.039,
EMS
:
0.001);
treatments
on
a
per plant basis and
con-
verted
to a land area basis.
RSS and
EMS denote
residual
sum
of squares
and error
mean
square,
resDectivelv.
Statistical
Analysis
Variables were
subjected
to the
analysis of
vari-
ance
[GLM
procedure
of Statistical
Analysis
System
(SAS),
SAS
Institute
19851, to determine
main treatment effects and
interactions.
Data from
both
years
were combined
for
analysis,
and tested
separately
when results showed statistical
differ-
ences between
years.
Yield-plant
population
den-
sity responses in 1988 were defined
using
a non-
linear regression
procedure
IBMDPAR
(Dixon
1985)l according to a
model ofBleasdale
(1967):
y":d+px
where
,y
represents mean
yield
plant-l and
1
represents
plant population
density.
Parameter
o
is
an
index of
plant
yield
in the absence
of compe-
tition, and
B
is an index of the
responsiveness
of
a
plant
to
population
density
changes.
Parameter
0 is thought to be
related to the utilization
of
environmental
resources in the space
accessible to
a
plant
tWatkinson
1984).
05c
Economic
Analysis
Net economic
costs and
returns
of
each
treatment
were compared
to
a
population
density
of 2.'78
plants m
',
without
row covers.
This density
most closely
corresponds
to
the
current
commer-
cial
planting density
in
British Columbia.
Trans-
planting costs
were
based
on
machine
harvesting
and included
machinery
operation,
depreciation,
interest on the
investment,
and
labour
(M.
Sweeney
1991,
BCMAFF,
personal communication).
Returns
were
based
on
the
landed
costs
of
green
peppers to
wholesalers
in
Vancouver, BC
in
1988
and
1989
(J.
Atcock
1991,
BCMAFF,
personal
communication).
RESULTS
Air
Temperatures
Ambient temperafures
were
generally
warmer
in
July
and August
of
1988 than
in 1989
(data
not
presented).
Row covers
elevated
daily
mean air temperature
as
much
as
4oC
above
p
y
8/9/2019 Row Cover & Population Density Effects on Yield of Bell Peppers in South Coastal British Columbia; Gardening Guidebook
4/9
904
CANADIAN
JOURNAL
OF
PLANT
SCIENCE
uncovered
trgatments.
Daily
mcan
tempera-
ture
under
the row
covers
was
never
greater
than
27"C
in
1988
and
29"C in
l989]Mean
daily
maximum
temperatures
for rhe
3-d
period
following
transplanting
in
1988 were
23'C
and
35'C
for
uncovered
and
covered
plots,
and
29'C
and
39"C,
respectively,
in
1989.
Also.
maximum
air
temperature
under
the row
covers
was greater
than 40"C
on
19 d
in
1988
and
I
I
d
in
1989.
Vegetative
Dry
Matter
Yield
The
application
of row
covers,
and
interac-
tions
between
row
covers
and plant
popula-
tion
density,
did not
influence
vegetative plant
components.
The
yield
of plant
components
decreased
linearly
with
increasing
population
density
(data
not presented).
Total vegetative
yield,
but
not the
yields
of
vegetative plant
components,
were
satisfactorily
fit
to Bleas-
dale's
model.
Vegetative
yield
decreased
in
response
to
increasing
population
density
When
measured
on
a
per-plant
basis,
but
increased
on
a
per-land-area
basis
(Fig.
l).
Fruit
Yield
FRUIT
CHARACTERISTICS
AND
UNMAR-
KETABLE
FRUIT.
Fruit
size
{g fruit
l;
was
larger
in
1988
than
1989
(124
and
109 g,
respectively).
Fruit
iength,
over
all
treatments,
was
9.7
and
10.0 in
1988
and 1989.
resDec-
tively:
mean
fruit width
was
7.5 in
1988
and
7.0
in
1989.
Treatment
effects
on fruit
size
and
shape,
when
detected,
were
small
and not of
horticultural
significance
(data
not presented).
Satisfactory
fits
to
nonlinear
models
were
not
obtained
for
unmarketable
fruit:
hence.
ANOVA
results
are
presented
(Table
l). The
percentage
of marketable
fruit
was
higher
in
1988
than
1989
(80
and
58%. respeciively).
but
was generally
not
affected
by
treatments.
The
exception
was
a
significant
linear
trend
in
1988
showing
a decrease
in
the
percentage
of
marketable
fruit with
increasing
population
density.
The
yield
of undersized
fruit was
greater
in
1989
than
1988,
but the quanrity
of
diseased
fruit
did not
differ
between
the
years.
EnnIyFRUITYIELD.
Row covers
enhanced
early marketable
fruit
yield
and
total early
fruit
yield
in 1988 but not in
1989
(Table
l).
These results
were
probably
due
to
the
high
temperatures
that
followed
transplanting
in
1989.
Many
plants
were
stressed
and showed
symptoms
of sunscald.
In
1988 early mar-
ketable fruit
yield
was
90%
greater
from
covered
than
uncovered treatments.
The
curves
shown in
Fig. 2
represent
the
best fit
of
the
regression
equation for
1988 early mar-
ketable yield.
Early
yield
per
land
area
increased
in
response
to increasing population
density in 1988 and
1989.
In
1988,
a signifi-
cant
row-cover-by-population-density
interac-
tion
indicated that
row
covers had
a
greater
influence on
early
yield
at low
population
den-
sities
than
at high
densities.
In
both
years,
early
yield per
land
area increased in response
to
increasing population
density. 1989
early
yield
data showed
extreme
variability
between
plants
and
satisfactory
fits to nonlinear
models
were not
obtained.
Ovenelr- FRUIT
yrELD.
In
both
years,
row
covers
enhanced overall
marketable
fruit
yield
(Table
1).
Fruit
yield
per plant
decreased and
yield
per
land
area increased, in response
to
increasing population
density
(Fig.
3). A sig-
nificant
interaction
showed
that the
influence
of
row
covers
on marketable
yield
per plant
declined
with
increasing
population
density.
Interactions
on a
per-land-area
basis were not
significant.
Economic
Analysis
The
application of row
covers increased net
costs
above
the
current industry
population
density
standard
(2.78
plants
m-')
at all
population
densities
(Table
2).
Planting
at
the
highest
population
density tested. I l.l
plant
m
'.
increased
net
costs by
$5741
ha
I
without
row covers
and by 57795
ha-l
with
row
covers.
Net economic
returns
increased with
increasing population
densities
higher
than the
standard, but returns were
greatest
with
the
addition
of row covers.
Row
covers
also
increased
returns when
used at the industry
standard. The
largest net
economic return,
$19815
ha
'
above
the standard, was
obtained
from
covered
plants grown
at the
p
y
8/9/2019 Row Cover & Population Density Effects on Yield of Bell Peppers in South Coastal British Columbia; Gardening Guidebook
5/9
905
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8/9/2019 Row Cover & Population Density Effects on Yield of Bell Peppers in South Coastal British Columbia; Gardening Guidebook
6/9
906
CANADIAN JOURNAL
OF
PLANT
SCIENCE
0369t2036912
POPULATION DINSITY,
plonts
m-'
Fig.
2. Means
and nonlinear
reg_r-essions
of 1988
early
marketable fresh ftuit
yield
on
population
den-
sity
for
uncovered,
-
(l-uuror
:
t.0 + 0.00293X, RSS
:
6.7,
EMS
:
0.087), and covered,
----- (i
r56
:
-0.23
+
0.438X,
RSS
:
18.3, EMS
:
0.23'7); rreatments on a
per-plant
basis and
converted
to a land-area
basis.
RSS
and EMS
denote
residual
sum of squares
and
error
mean
square,
respectively.
6.0
N
|
4.5
C
L
f