THE EFFECT OF CLEAR AND BLACK POLYETHYLENE AND PAPER MULCHES WITH
REEMAY ROW COVER AND THREE ROW PLANTING PATTERNS ON OKRA
PRODUCTION
Victor A. Khan1, Clauzell Stevens1, Mack A. Wilson2, Daniel J. Collins3, James E. Brown4,
Emmanuel C. K. Igwegbe1 and John Y. Lu1
'GEORGE WASHINGTON CARVER AGRICULTURAL EXPERIMENT STATION, TUSKEGEE UNIVERSITY., TUSKEGEE
INST. AL 36088.
'DEPARTMENT OF AGRICULTURE SOUTHEAST MISSOURI STATE UNIVERSITY, CAPE GIRARDEAU, MO 63701.
'DEPARTMENT OF PLANT PATHOLOGY, AUBURN UNIVERSITY, AUBURN AL 36894.
'DEPARTMENT OF HORTICULTURE, AUBURN UNIVERSITY, AUBURN AL 36849.
Abstract: Eight wk. old 'Clemson Spineless' okra transplants were grown on clear
(CM) and black (BM) polyethylene and paper (PM) mulches with and without Reemay row
cover, in three planting patterns (single, double and equilateral). Results showed that BM
treatment had greater soil temperature than PM and bare soil (BS) while PM was 4° F cooler
than BS at the 5 em soil depth. Marketable pod yields and numbers were greater for BM and
PM mulched plots compared to BS treatment. However, BM produced greater yield than PM
on single row planting pattern. Double and equilateral planting patterns had significantiy
higher yields than single planting pattern. The number of secondary branches were greater on
plants grown on BM and PM than BS. Secondary branching was greater on single plant row
pattern compared to double and equilateral.
Keywords: Plastic Mulches, Black Paper Mulch, Planting Patterns, Okra
Introduction
Postplant application of clear (CM) and black (BM) polyethylene mulch with VisPore plus clear
mulch, VisPore plus black mulch (VCM, VBM) is a form of soil solarization (7) resulting in the increase
growth response (IGR) and early production of fruits and vegetables during early spring (2, 3, 5). The
current mode of actions or mulching effects which explains how postplant agri-plastic mulches improves
growth and yield of fruits and vegetables are: water conservation, utilization of fertilizers, gas exchange
between air and soil, weed control and temperature modifications (8). In a recent study, IGR of vegetables
such as yield and number of fruits produced was observed on transplants grown on postplant CM and BM
agri-plastic mulch systems with and without row cover, showed significant shift in the rhizobacteria in the
rhizosphere, rhizoplane soil and interior root tissue in vegetable crops grown on these mulch systems
compared to bare soil (BS) (2,5).
In addition to the use of agri-plastic mulches to promote IGR, modifying the number of plants per
row can also increase the IGR of crops (6). Therefore, this study was designed to compare the IGR of
'Clemson Spineless' okra plants when grown on CM and BM and black paper (PM) mulches with and
without row cover and planted in three different planting patterns compared to BS.
Methods and Materials
This study was conducted at the George Washington Carver Agricultural Experiment Station,
Tuskegee University Alabama, on Norfolk sandy loam soil (Typic Paleudult). Plots were arranged in a
split-split-plot randomized design with four replications. Eight week old 'Clemson Spineless' transplants
were transplanted on April 15, 1996, in the following treatment sequence: clear polyethylene (CM), black
polyethylene (BM), black paper mulch (PM), CM plus Reemay row cover (R) (Reemay is a trade name
and is manufactured by Ken-Bar Corporation, Reading MA ), BM plus R (RBM), PM plus R (RPM), BS
and BS plus R (RBS).
Field plots were established by forming a bed 14 x 2 ft. and applying the recommended NPK
fertilizers in a single band. All plots were drip irrigated with an 8 mil turbulent drip irrigation tube which
84
was placed off-center of the bed. Dacthal herbicide was applied at the rate of 3 lbs per acre to RCM, CM,
RBS and BS plots before mulch or row cover application. 'Clemson Spineless' okra transplants were
grown in commercial medium (Jiffy Mix) in PVC trays in the greenhouse. Seedlings were placed 2 ft.
apart within the rows, giving 7 , 14 and 13 plants per plot for single, double and equilateral planting
patterns, respectively (Fig. 1). All row covers were hoop supported and were placed over the transplants at
the time of transplanting.
Soil moisture tension was determined by using tensiometers in all mulched treatments at 4 and 8
inch depths and water was applied when the water potential reached 20 centibars. Soil temperature was
measured at the 5cm soil depth with a temperature recorder (Foxboro Corp., MA.). All row covers were
removed 30 days after application. IGR collcctcd were marketable yield, number of okra pods and the
number of secondary branching. Gramaxone herbicide was applied to control weeds between the rows.
All data were statistically analyzed using the analysis of variance (ANOVA) and means were compared by
orthogonal contrasts (10).
Results
Table 1 shows the soil temperature data during April and May 1996 for BM, PM, BS and air,
without R at the 5 cm soil depth. The data indicate that the maximum soil temperature under PM at 1 -6
p.m. did not exceed that of BS. The maximum soil temperature of BM, PM and BS, were 87.6, 78.9 and
81.3° F, respectively during the month of May. Maximal soil temperature under CM was 93° F (Data not
shown).
The yield and number of okra pods of plants in the single row planting pattern were greater when
grown on BM and RBM than CM, RCM, BS and RBS (Tables 2A, 3A). With few exceptions (RCM) PM
produced significantly less yield and number of okra pods than the CM and BM polyethylene mulches with
and without R. Also, okra plants grown on PM produced greater yield and number of pods. Tables 2 A
shows a significant three way interaction among row cover X mulches X planting patterns therefore, each
combination of the factors were examined separately. Table 2B shows that the interaction of mulches X
row covcr indicates that BM, PM and BS, had significantly higher yields without R whereas, CM did not
show any great differences in yield with R or without R irrespective to planting patterns. The data for
mulch X planting patterns interaction indicate that (Table 2C) when okra transplants were grown on CM or
BS the yields tended to be linear as the planting patterns changed from single to equilateral. The yield
from plants grown on BM and PM reached peak production at the double and declined at the equilateral
planting pattern, irrespective to row cover (R). Planting patterns X R (Table 2D) interaction showed that
in the absence of R, yield was greater at either double or equilateral planting patterns, while R affected
transplants grown in the single planting pattern irrespective to mulches .
Data for the production of the number of okra pods also showed a significant three way interaction
(Table 3A). The interaction between mulches X R indicates that the number of pods produced by
transplants grown on CM, BM and PM mulches without R were greater, while the use of R only affected
the yield of BS, irrespective to planting patterns (Table 3B). The interaction between mulches X planting
patterns shows that CM and BM produced their highest number of pods at the double planting pattern;
while PM and BS showed a linear increase in the number of pods as the planting patterns changed from
single to equilateral, irrespective to R (Table 3C). The R X planting patterns interaction shows that the
highest number of okra pods were produced at the double and equilateral planting patterns without R.
While transplants grown on single planting pattern with R had higher pod numbers irrespective to mulches
(Tabic 3D).
Table 4 shows that the highest number of secondary branches on all okra transplants grown on
mulches or BS, with R or without R at the single planting pattern, compared to the double and equilateral.
Overall, when R was used in combination with the mulches, a higher number of secondary branches were
produced compared to NR.
85
Discussion
The results from this study showed that polyethylene mulches, R and planting patterns,
significantly increased the IGR of okra as indicated by marketable yield, number of okra pods and number
of secondary branches produced by 'Clemson Spineless' okra transplants. Commercial okra producers
currently uses single plant row pattern; thefindingsof this study showed that by changing the planting
pattern to either double or equilateral planting patterns yields were almost doubled. The lower yield
obtained with RCM and CM when compared to RBM and BM at the single planting row pattern was
probably due to the effects of the Dacthal herbicide. It has been reported that this herbicide significantly
reduced yield and surpressed the rhizobacteria population in the rhizosphere of collards green plants (9).
Previous studies (2, 5) using both pre- and post-plant agri-plastic mulch system, have reported IGR of
several vegetable crops with a corresponding microbial shift in the rhizobacteria around the root system.
These studies also indicated that the soil temperatures which existed under the polyethylene mulches by
solar heating though not very high as those reported under pre-plant plasticulture studies (5, 7, 9) were
great enough to cause a microbial shift in favor of beneficial rhizobacteria that stimulates IGR (11),
especially when R was used.
The most interesting resultfromthis study was the greater yields PM had on okra grown in single
planting pattern without R compared to the BS. And yet the soil temperature under PM was 2.4° F less
that that of BS and almost 8 .7° F less than BM during May 1996. This data suggests that the effect of PM
could be due to the insulating properties of PM which prevented solar heating and probably prevented a
shift of rhizobacteria around the roots of okra plants (5). Previous reports have indicated that BM
increases the soil temperature over the BS by as much as 10° F (7). Recently, it has been postulated that a
mild form of solar heating caused a shift in the rhizobacteria population in the root environment and
increase the IGR of vegetable crops (5). The contrasting results of the IGR of okra grown on BM vs PM
suggest that water conservation, weed control, utilization of fertilizers and gas exchange between air and
soil are the main mulching effects or "mode of action" which accounts for the IGR of okra grown on PM
compared to BS. However, shifts in the rhizobacteria population in the root environment is one mode of
action along with the foregoing which explains IGR okra grown on BM (8, 5). The dcficit of the IGR of
okra grown on PM probably is indicative of two things a). PM lacks thermal conduction and b). it has
previously been reported that the black pigment on BM reflects very little of the incoming radiation to the
canopy of a crop (1). Therefore, reflected radiation would not influence IGR of okra grown on PM.
Further studies will be needed to determine the influence of PM on the soil microflora and changes in the
root environment.
The main effect of the different row planting patterns in this study showed increased yield for okra
when compared to the traditional single plant row system (6). The additional benefits were reduced
irrigation and water costs (data not shown) and the quality of the crop was not affected. The amount of
secondary branching per plant was greatest on plants grown at the single plant row pattern compared to
double and equilateral planting patterns. This maybe due in part to crowding effect which arosefromthe
increase plant population found in the double and equilateral planting patterns. It should also be noted that
the amount of secondary branching report in this study was approximately doubled for the mulch plus R
treatments than was previously reported for okra (4).
Conclusions
Yields from black paper mulch was significantly greater than bare soil but had lower
soil temperature readings. While mulches plus no row cover produced better yields than when used with
row covers except CM at this planting date. Double and equilateral planting patterns produced
significantly more okra pods than single row planting pattern. And more secondary branches were
produced by plants grown on the single plant row pattern compared to double and equilateral.
Literature cited
1. Fortnum, B A., Decoteau, D. R., Kasperbauer, M J and Bridges, W. 1995. effect of colored mulches
86
on root-knot of tomato. American Journal of Phytopathology Vol. 85:312-318.
2. Khan, V. A., Stevens, C., Wilson, M. A., Brown, J. E„ Collins, D. J., Lu, J. Y. and Mafolo, T. 1994.
Relationship between rhizosphere microflora and increased growth response of Crimson
Sweet watermelon grown on clear and black plastic mulch plus VisPore row cover. American
Society of Plasticulture. 25:122-129.
3. Khan, V. A., Stevens, C., and Tang, A. Y. 1989. Effect of VisPore row cover and polyethylene mulch
on early production of watermelon in Alabama. Proc. Nat. Agr. Plastics Congr. 21:252-255.
4. Khan, V. A., Stevens, C. and Brown, J. E. 1990. Early response of transplanted okra grown under
VisPore row cover and two types of polyethylene mulch. National Agricultural Plastics Congress.
22:28-32.
5. Khan, V. A., Stevens, C., Wilson, M. A., Brown, J. E., Collins, D. J., Lu, J.Y., Mafolo, T. and
Rhoden, E. G. 1997, Evidence of soil microflora change associated with increased growth
response of vegetables grown on agrimulch systems. International Congress for Plastics in
Agriculture. (In press).
6. Singh, S. D. 1978. Effects of planting configuration on water use and economics of drip irrigation
systems. Agronomy Journal. Vol. 70. 951-954.
7. Stevens, C., Khan, V. A., Brown, J. E., Plopper, L. D., Collins, D. J., Wilson, M. A.,
Rodriguez-Kabana, K. and Curl, E. A. 1993. The influence of soil solarization as related to
changes in the soil rhizosphere. American Society for Plasticulture. 24:170-188.10.
8. Stevens, C., Khan, V. A., Brown, J. E. Hochmuth, G. J., Splittstoesser, W. E. and Granberry, D. M.
1991. Plastic chemistry as related to plasticulture and solar heating of soil. Chapter 8,
pp.141-158. Soil Solarization. Katan, J. and DeVay, J. E. Eds. CRC press, Boco Raton.
9. Stevens, C., Khan, V. A., Okoronkwo, T., Tang, A. Y., Wilson, M. A., Lu, J. Y. and Brown, J. E.
1990. Soil solarization and Dacthal: influence on Weeds, growth and root microflora of collards.
Hortscience 25:1260-1262.
10. Snedecor, W. G. 1966. Statistical Methods. Iowa state University Press, Ames. pp. 237.
11. Young, S., Pharis, R. P., Reid, D., Reddy, M. S., Lifshitz, R. and Brown, G. 1991. PGPR: Is there
a relationship between plant growth regulations and stimulation of plant growth or biological
activity? pp. 182-186. Plant growth promoting rhizobacteria- Progress and Prospects. Eds. K. C.
Skoller and G. Defago. The second International workshop of plant growth Promoting
Rhizpbacteria. Interlaken S w i t z e r l a n d Oct. 14-19, 1990.
87
FIG. 1 PLANTING CONFIGURATION
88
Table 1. Mean soil and air temperature (°F) recorded for black polyethylene plastic mulch (BM), black paper (PM) mulch and bare soil
(BS) at 5 cm soil depth.
Treatments
oo
<0
April
7AM-Noon
m
Mav
m
1-6PM
April m
Mav
m
7PM-Midnight
April f°F)
Mav
m
April
1AM-6AM
m
Mav C°F)
BM
68.92
78.49
74.80
87.63
66.05
76.78
58.11
70.43
PM
58.78
67.25
69.14
78.90
58.02
68.23
53.40
62.58
BS
60.06
71.52
69.82
81.32
56.88
70.44
49.85
64.08
Air
62.10
75.42
60.67
85.49
75.26
67.47
53.08
59.37
Table 2A. Mean yield (cwt/acre) of 'Clemson Spineless' okra grown on clear (CM) and black (BM) polyethylene, black paper (PM)
mulches and bare soil (BS) with and without Reemay (R) row cover.
Mulches plus row cover
Planting
patterns
RCM
RBM
Single
276
621
Double
622
615
Equilateral
510
534
Significance of F test from ANOVA
Mulch vs No mulch
Reemay vs No Reemay
Planting methods
Mulches X Reemay
Mulches X Planting patterns
Reemay X Planting patterns
Reemay X Mulches X Planting patterns
RPM
162
539
537
Mulches with no row cover
RBS
277
327
242
CM
280
501
624
BM
480
780
683
PM
348
714
450
BS
144
376
545
**
**
* *
**
**
**
**
**, *, NS significant at the 1%, 5% and not significant, respectively.
Table 2B. Mulch X R
on total yield
Reemay
NoReemav
4,224
4,216***
CM
5,310
5,828
BM
4,535
PM
3,715
3.194
2.535
BS
Table 2C. Mulches X Planting Patterns
on total yield
Single Double Equilateral
1,123
1,134***
CM
556
1,217
BM 1,101
1,395
987
510
1,253
PM
787
421
703
BS
***,The values in Table 2B, 2C and 2D, are the sum total for each treatment.
Table 2D. R X Planting Patterns
on total yield
Reemay
No Reemay
1,336
1,252***
Single
Double 2,103
2,371
2.302
Equilateral 1.823
Table 3 A. Mean number ('OOO/acre) of'Clemson Spineless' okra grown on clear (CM) and black (BM) polyethylene, black paper (PM)
mulches and bare soil (BS) with and without Reemay (R) row cover.
Mulches plus row cover
Planting
patterns
RCM
RBM
Single
74
88
Double
143
107
Equilateral
111
96
Significance of F test from ANOVA
Mulch vs No mulch
Reemay vs No reemay
Planting methods
Mulches X Row cover
Mulches X Planting patterns
Reemayr X Planting patterns
Reemav X Mulches X Planting patterns
RPM
31
92
114
Mulches with no row cover
RBS
31
66
76
CM
73
122
149
BM
73
136
132
PM
44
107
95
BS
19
47
58
**, *. NS significant at the 1%, 5% and not significant, respectively.
Table 3B. Mulch X R
on total numbers of pods
Reemay
No Reemay
CM
985
1,033***
BM
871
1,024
PM
713
738
521
BS
375
Table 3C. Mulches X Planting Patterns
on total numbers of pods
Single Double Equilateral
265
260***
147
CM
228
243
BM
161
199
209
PM
75
113
134
50
BS
***,The values in Table 2B, 2C and 2D, are the sum total for each treatment.
Table 3D. R X Planting Patterns
on total numbers of pods
Reemav
No Reemay
209***
224
Single
412
408
Double
434
Equilateral 397
Table 4. Mean number of secondary branches/plant of'Clemson Spineless' okra grown on clear (CM) and black (BM) polyethylene,
black paper (PM) mulches and bare soil (BS) with and without reemay (R) row cover.
Mulches plus row cover
NÌ
Planting
patterns
RCM
Single
6
Double
4
Equilateral
5
Significance of F test from ANOVA
Mulch vs No mulch
Reemay vs No Reemay
Piantina methods
RBM
6
4
4
RPM
4
3
2
Reemav X Mulches X Planting patterns
**, *, NS significant at the 1%, 5% and not significant, respectively.
Mulches with no row cover
CM
4
3
2
RBS
3
2
2
* *
* *
* *
BM
4
3
4
PM
3
3
2
BS
2
2
1