April 2011
Cotton response to plant distribution pattern
at low population
Guangao (Sam) Wang
Maricopa Ag Center, University of Arizona
Summary
Unintended low plant populations due to weather conditions or management
practices often occur with inconsistent stands. In this case, both plant
population and plant distribution pattern might affect lint yield. A field
experiment was conducted at University of Arizona’s Maricopa Agricultural
Center to investigate the effects of plant distribution pattern on cotton growth
and production using two varieties ST 4498 (bush type) and DP161 (columnar
type) under 20,000 plants/acre population. The treatments include a uniform
distribution (UD), random distribution (RD), segmentary distribution with 2foot gaps (SD2), and segmentary distribution with 4-foot gaps (SD4). RD, SD2,
and SD4 resulted in longer time periods for canopy closure with reduced lint
yield compared to the UD treatment. Both varieties showed similar pattern, but
yield reductions in RD, SD2, and SD4 treatments compared to the UD treatment
were smaller for the bush type variety ST 4498 than the columnar type variety
DP 161. Plant distribution factor should be considered in re-planting decisions.
Introduction
Currently, the recommended cotton plant population in Arizona is in the range of 25,000-50,000 plants/ac
(Silvertooth, 2001). Using a lower planting density while maintaining cotton yield is desirable for growers to reduce
cost on seed input and increase profitability. This is more important in recent years due to dramatically increased
cost of cotton seed and technology fees. For example, seed cost increased from about $0.7/lb in 1996 to about $7/lb
in 2010, a 10-fold increase.
Inclement weather during planting may result in less than optimal germination and low plant density. Lower plant
populations (10,000-15,000 plants/acre) will need longer to grow into a closed canopy and still produce acceptable
yields in Central Arizona (Galadima et al., 2003). However, space and sunlight are likely not fully utilized under
low plant population resulting in reduced yield.
At the same time, unintended low plant populations often result with inconsistent stands. In this case, not only plant
population, but plant distribution pattern might affect lint yield. Varieties with different growth habits (i.e. bush type
or columnar type) might have a different optimal plant population for maximum production and respond to plant
distribution patterns differently. An experiment was conducted in 2010 to investigate the effects of plant distribution
pattern on cotton growth and production using two varieties with different growth habits under low plant population.
Materials and Methods
The field experiment was conducted at the University of Arizona, Maricopa Agricultural Center, Maricopa, AZ in
2010. Seeds were planted on 40-inch beds at 50,000 plants/acre on April 7, 2010. The beds were watered up the
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following day. Two cotton varieties were used in this study: a bush type Stoneville ST-4498-B2RF (ST 4498) and a
columnar type Delta and Pine Land 161-B2RF (DP 161).
The experiment was a randomized complete block design with four replications. Each plot was four rows wide and
35 feet long. The final plant population for all plots was 20,000 plants/acre. Four plant distribution patterns were
established on May 6:
(1) Uniform distribution (UD): cotton plants were uniformly distributed at an in-row spacing of about 7.85
inches;
(2) Random distribution (RD): cotton plants were thinned in a random pattern generated by a computer
program to the desirable density of 20K/A;
(3) Segmentary distribution (SD2): 2-foot gaps were cut within each bed and cotton plants were thinned to
20,000 plants/acre. The gaps between adjacent beds were cut in a zigzag pattern.
(4) Segmentary distribution (SD4): Similar to treatment 3, but with 4-foot gaps.
The crop was managed following common practices in Central Arizona. The last irrigation was applied on
September 2 and the plants were defoliated in late September. Cotton plants from the middle two rows were
harvested on November 10 using a two-row cotton picker. After harvest, seed cotton samples were ginned in a
Mitchell gin machine to determine gin turnout and lint yield from each plot. A sub-sample of lint (40-50 g) was sent
to the Materials Evaluation Laboratory, Texas Tech University (Lubbock, TX) for high volume instrumentation
(HVI) fiber quality analysis.
Results and Discussion
Cotton growth response to plant distribution pattern
There were no significant visual differences among the treatments with respect to plant growth and development.
An aerial view picture taken from a helicopter 85 days after planting showed complete canopy closure in the UD
treatment (Figure 1). Gaps were visible in the RD treatment. In SD2 and SD4 treatments gaps were still significant.
Although plants in all treatments formed a closed canopy at later growth stages, this trial clearly showed UD had
advantages in utilizing space and sunlight compared to other treatments.
UD
RD
SD2
SD4
SD2
UD
SD4
RD
ST
4498
DP
161
Buffer
Figure 1. Aerial view of the two middle blocks at 85 days after planting on July 1. The original plant distribution
pattern treatments were still visible. UD: uniform distribution; RD: random distribution; SD2: segmentary
distribution with 2-foot gaps; SD4: segmentary distribution with 4-foot gaps.
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Cotton yield response to plant distribution pattern
The UD treatment had the highest lint yield with 1829 and 1667 lb/acre for DP 161 and ST 4498, respectively
(Table 1). For DP161, the RD, SD2, and SD4 treatments reduced cotton lint yields by 10.3%, 7.8%, and 19.4%,
respectively, compared to the UD treatment. With respect to bush type variety ST 4498, lint yield differences
between RD and SD2 treatments were not significant, but the SD4 treatment reduced cotton lint yield by 15.8%
compared to the UD treatment.
This study showed that random and segmentary distribution with 2 or 4-foot gaps could reduce lint yield. Therefore,
the plant distribution factor needs to be considered in the replanting decision. Although response of the bush type
variety ST 4498 had the same trends as the columnar type variety DP 161, it seems that yield reductions for the bush
type variety were slightly lower than the columnar type variety when plants were not uniformly distributed.
Table 1. Lint yield response for a bushy type variety ST 4498 and a columnar type variety DP 161.
treatment
Lint yield (lb/acre)
Variety
UD*
1829 a**
RD
1640 b
DP 161
SD2
1685 b
SD4
1474 c
ST 4498
UD
RD
SD2
SD4
1667 a
1522 ab
1558 ab
1405 b
* UD: uniform distribution; RD: random distribution; SD2: segmentary distribution with 2-ft gap; SD4: segmentary distribution with 4-ft gap.
** Means followed by the same letter are not statistically different according to a Fisher's least significant difference means separation test.
Fiber quality response to plant distribution pattern
For both DP 161 and ST 4498, plant distribution pattern did not affect gin turnout and fiber quality, except that UD
and RD treatments had larger elongation than SD2 and SD4 for DP 161 (Table 2). The treatments with ST 4498 did
not show a similar trend. These preliminary results do seem to indicate that inconsistent stands can have a significant
effect on crop yield. Further study is required to better identify and confirm these effects.
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Table 2. Cotton fiber quality response to plant distribution pattern
Gin
Length Uniformity
Variety Treatment turnout Micronaire
(inch)
(%)
(%)
UD*
4.56
1.16
81.6
32.2
RD
4.67
1.16
81.4
DP
31.7
161
SD2
4.55
1.19
82.2
32.4
SD4
4.57
1.17
82.0
32.5
Strength
(g/tex)
31.2
30.5
31.1
30.7
Elongation
(cm)
6.20 a **
6.03 a
5.60 b
5.63 b
Grayness
(Rd)
Yellowness
(+b)
Color
grade
Leaf
grade
Premium
(cents/lb)
81.8
81.7
81.4
81.3
7.00
7.00
6.95
6.78
31
31
31
31
2.25
2.50
2.50
1.75
5.29
5.25
5.35
5.20
UD
4.46
1.10
82.2
31.8
7.38
80.5
8.25
21
2.50
5.34
34.8
RD
4.35
1.09
81.9
31.7
7.40
80.6
8.25
21
2.25
5.44
34.5
SD2
4.50
1.10
82.3
31.6
7.85
80.7
8.15
21
2.75
5.33
34.7
SD4
4.33
1.11
82.5
32.3
7.50
80.3
8.13
21
3.25
5.48
34.7
* UD: uniform distribution; RD: random distribution; SD2: segmentary distribution with 2-foot gap; SD4: segmentary distribution with 4-foot gap.
** Means followed by the same letter are not statistically different according to a Fisher's protected least significant difference means separation test.
ST
4498
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References
Silvertooth, J.C. 2001. Plant Population Evaluation/Management for Cotton.
http://cals.arizona.edu/pubs/crops/az1203.pdf
Galadima A., S.H. Husman, and J.C. Silvertooth. 2003. Plant population effect on yield and fiber quality of three
upland cotton varieties at Maricopa Agricultural Center, 2002.
http://www.cals.arizona.edu/pubs/crops/az1312/az13121e.pdf
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