Upland Cotton Lint Yield Response to Several
Soil Moisture Depletion Levels
S. Husman, Pinal County Cooperative Extension
K. Johnson, Pinal County Cooperative Extension
R. Wegener, Pima County Cooperative Extension
F. Metzler, Pinal County Cooperative Extension
Upland cotton lint yield response to several soil moisture depletion levels
was measured in 1996 and 1997 for four Upland cotton varieties including
DP 5415, DP 33B, DP 5816, and STV 474. In 1996, depletion of plant available
soil water (PAW) irrigation treatments consisted of 35%, 50%, 75%, and 90%.
In 1997, treatments were 35%, 50%, 65%, and 80% depletion of PAW. In 1996,
the 35% and 50% treatments were significantly different than the 75% and 90%
treatments (P<0.05) and resulted in the highest lint yields of 1374 and 1438
lbs. lint/acre respectively. A lint yield reduction was measured with the
75% and 90% PAW treatments of 713 and 329 lbs. lint/acre, respectively.
The 75% and 90% treatments were significantly different than the 35% and 50%
treatments and were significantly different from each other. In 1997, all
PAW depletion treatments were significantly different with the 35% PAW treatment
resulting in the highest average lint yield of 1880 lbs. lint/acre. The 50%,
65%, and 80% PAW treatments resulted in 1410, 1123, and 248 lbs. lint/acre
respectively. There was no significant (P<0.05) difference between
varieties within all PAW treatments in 1996 or1997.
The Arizona cotton production system is unique when compared with the
majority of the United States cotton belt. Due to the semi-arid climate
and high summer temperatures, all the cotton acres are irrigated. Due to
high input costs, high lint yields are needed in order for farms to remain
competitive and profitable. The low desert of Arizona has a long, growing
season, which is an advantage compared with the remainder of the cotton belt.
Historically, Arizona production systems have capitalized on the
production potential of full season varieties, commonly resulting in high
yields. However, as a result of increasing late season insect pressures,
increasing costs of production, and static cotton prices, Arizona cotton
producers have generally shifted toward a reduced season production approach
in contrast to the historical full season system.
Low desert producers have adopted a late season insect avoidance strategy
with an attempt to produce maximum economic yield versus maximum agronomic yields.
However, the increasing input costs and static cotton prices continue to require
high lint yield production in order to survive economically. In addition to late
season insect avoidance strategies, a second production change is the use of
cotton varieties which are earlier with respect to maturity than historically
produced varieties. The earlier maturity varieties tend to have a stronger and
more compacted primary fruit cycle than the historically produced longer
maturity varieties. High yield potential exists with the currently used
earlier maturity varieties but tend to offer less late season production
opportunity and mandate utilization of highly efficient production inputs
during the primary flowering cycle.
Since the shift toward earlier maturity varieties, producers have observed
that optimum in season water management is critical if high yields are to be
realized consistently. This experiment was designed to evaluate lint yield
response to specific soil moisture depletion levels between irrigation
intervals from planting through cut out, representative of a single fruit
set production system. The primary objective was to measure lint yield
response to soil moisture depletion levels of four popular varieties.
Materials and Methods
The experiment was conducted at the University of Arizona Maricopa Agricultural
Center on a Casa Grande sandy loam soil in 1996 and 1997 and consisted of four
irrigation treatments based on soil moisture depletion levels between
irrigation events. In 1996, the irrigation treatments were 35%, 50%, 75%,
and 90% depletion of plant available soil moisture depletion.. In 1997,
irrigation treatments were modified to include 35%, 50%, 65%, and 80%
plant available soil moisture depletion in order to more accurately identify
the critical level of soil moisture depletion responsible for yield reduction.
Within each irrigation treatment, there were four Upland cotton varieties
including DP 5415, DP 33B, and STV 474, and DP 5816.
Plots were sixteen rows (forty inch spacing) wide and one hundred seventy
feet long. Each sixteen row irrigation treatment main plot contained the four
varieties, each subplot four rows wide. The experiment consisted of four
irrigation treatments replicated four times resulting in a split plot design
within a randomized complete block. The test field was pre-irrigated and
planted to moisture on April 2, 1996 and April 9, 1997 with a fourteen lbs./acre
seeding rate. All subsequent plot irrigations were accomplished by pumping from
an adjacent irrigation ditch delivered through six inch aluminum pipe, metered
with an in-line McCrometer impeller flow meter, with individual plot water
delivery through six inch gated pipe.
Irrigation scheduling was accomplished by measuring soil moisture with a
Campbell Pacific 503 DR Hydroprobe. Several days after stand establishment,
two neutron probe access tubes were installed in every plot to a depth of
six feet. Neutron probe access sites were located in a center row, fifty
five feet from each end within the DP 5415 variety. Gravimetric soil samples
moisture samples and corresponding depth neutron probe measurements were
collected for each depth at the time of neutron access tube installation and
used for both field capacity determination and neutron probe calibration.
Gravimetric soil samples were collected from 0-30 cm and continued on
subsequent 20 cm increments to 190 cm.
Due to measured field capacity variability, each plot was assigned a measured
field capacity for each sampling increment. Each plot received irrigation
refill volume requirements on an independent basis relative to water holding
capacity and calculated plant available water. Soil samples were taken at
each neutron access site and each depth increment and analyzed for particle
size distribution. The textural triangle was used for soil texture determination
with available soil water determined by texture (USDA). The allowable soil
moisture depletion was calculated by multiplying the treatment depletion
threshold, (35%, 50%, 65%, and 80%) by the numerically determined total available
water value. Irrigation scheduling was accomplished by measuring soil
moisture content in each plot two days after each irrigation (gravity drainage
assumed complete) with subsequent soil moisture measurements at least every
other day until the targeted soil moisture depletion was attained. The active
root zone was estimated and expanded when water use occurred in the next 20 cm.
measurement increment since the previous irrigation event. When the targeted
soil moisture depletion threshold was attained, irrigation water was delivered
and measured the same day with the volume necessary to refill the soil profile
of depletion measurement for each plot.
Nitrogen fertilizer and pest control was managed on a liberal basis with
intents of eliminating yield affecting production variables
(Table 1 and 2).
Plant mapping measurements were made every other week from June through
mid-August within each irrigation treatment on all varieties. Measurements
included plant height, number of mainstem nodes, height to node ratio, and
nodes above top white bloom.
Cutout occurred across all treatments by late July in both 1996 and 1997.
Cutout is defined as measurement of nodes above top white bloom of five or
less. Irrigations were terminated on August 10, 1996 and August 13, 1997.
Defoliation (9 oz. Ginstar) was applied on September 5 in 1996 and 1997.
Defoliation was applied by ground with 18 gallons/ acre carrier rate.
Harvest was accomplished on September 18 and September 24 in 1996 and 1997
The center two rows of each four row subplot within each irrigation treatment
was harvested with a spindle picker. Harvested seed cotton was
weighed using a hanging electronic balance. The seed cotton was then
sub-sampled and ginned for lint percent. The lint samples were then
submitted to the USDA Cotton Classing Office in Phoenix, Az. for High
Volume Instrument (HVI) measured fiber lint quality characteristic
measurement (Table 3).
Results and Discussion
In 1996, the 35% and 50% soil moisture depletion treatments resulted in the
highest and statistically similar lint yields across all treatment
combinations (Table 4). There were no
significant variety yield differences by irrigation
treatment (Table 5). Lint yields were the
highest within the 35% and 50% depletion of PAW across all varieties. Yields
declined precipitously within all tested varieties within the 75% and 90%
PAW depletion irrigation treatments.
In 1997, all soil moisture depletion treatment yield responses were
significantly different (Table 6). There
were no significant variety differences within irrigation treatments
(Table 7). The highest lint yields were
obtained by all varieties within the 35% soil moisture depletion of
The results of these experiments indicate that there is not an irrigation
management response difference between varieties. All tested varieties
responded in a similar manner with in each irrigation regime. The results
of the two year experiment indicate that depletion of PAW should be managed
within a range of 35 -50%. Yield potentials of earlier maturity varieties
currently produced when managed for a primary fruiting cycle are high when
water is managed in an optimum manner. When depletion of PAW exceeds 50%,
yield decline is significant.
Both the 1996 and 1997 test results indicate that optimum irrigation
management during the primary fruiting cycle is essential to realize yield
potential . The highest yields occurred in 1996 when the peak irrigation
return interval was approximately ten days. In 1997, the 35% soil moisture
depletion treatment resulted in significantly higher yields than the remaining
treatments with a resultant irrigation return interval of seven days. Again,
the seven and ten day peak irrigation interval is representative of an optimum
irrigation management strategy targeting for a 35-50% depletion of plant
available soil moisture.
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- Kimbal, B.A., Mauney, J.R. (1993). Response of Cotton to Varying CO2, Irrigation, and Nitrogen: Yield and Growth. J. Agronomy. 85:706-712.
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This is a part of publication AZ1006:
"Cotton: A College of Agriculture Report," 1998, College of Agriculture,
The University of Arizona, Tucson, Arizona,
85721. Any products, services, or organizations that are mentioned, shown, or indirectly
implied in this publication do not imply endorsement by The University of Arizona.
The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az10065a.html
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