Potassium Fertilization of Upland and Pima Cotton (1991-1995, a five-year project review)
A. Galadima, Plant Sciences Department
J. C. Silvertooth, Plant Sciences Department
E. R. Norton, Plant Sciences Department
In an effort to provide information on the agronomic necessity of
potassium (K) fertilization in Arizona cotton (Gossypium spp.)
production, a five-year study was initiated in 1991 with a single field study
located near Gila Bend. Subsequent study sites selected ranged from western (Yuma)
to eastern (Safford) Arizona, which totaled 11 site-years. Both Upland
(G. hirsutum L.) and American Pima (G. barbadense L.) cotton
were cultivated, using soil and foliar applications of K. In 1992, study sites
included the Safford Ag. Center (SAC), Maricopa Ag. Center (MAC), and a
Cooperator site at Coolidge. In 1993, the experiment stations sites were
maintained (SAC and MAC) and Yuma Valley was added. The 1994 study sites included
only the two experiment stations (SAC and MAC). In 1995, SAC and MAC were
maintained, and a third location was a farmer cooperator site at Buckeye. The results
from all studies (12) indicated no lint yield increases due to K fertilization at
any of the locations with either Upland or Pima cotton. However, in 1995,at the
Buckeye location, the result
revealed a significant yield reduction due to the K foliar treatments. There
were, however, no significant
differences among soil as well as the soil-plus-foliar treated plots in the 1995
study at Buckeye.
Due to increased interest and reports of increased cotton yield as well as lint
quality, from various locations
across the U.S. cotton belt
from potassium (K) fertilization, a five year K fertility study was
initiated in 1991. Some notable studies of success on lint quality and yield
improvement resulting from
K input included those of Kerby and Adams (1985); Cassman et al. (1986-1992); Mullins et al. (1991); Oosterhuis et al. (1991); and Tupper et al. (1991a&b).
Potassium is an important
nutrient to cotton plants for many physiological processes; but it has
received considerable attention in its relation to fiber development. The development
of individual fiber cells are dependant upon the maintenance of adequate turgor
pressure within the cell (in the vacuole), which is controlled by a K+ malate
solute system (Dhindsa et al., 1975). As a result of the role of K in both the
vegetative and the reproductive structures of the plant, a study involving K
fertilization on cotton
yield could be valuable. The objective of this study was to assess the response of
commonly grown varieties of cotton in Arizona to foliar and/or soil applied K.
Materials and Methods
Beginning in 1991, a single field experiment was initiated at Paloma Ranch
in western Maricopa County (Gilman loam). The treatments imposed in the field (Table 1) were arranged as split plots within a
randomized complete block design (RCBD) with four replications. Soil applied
treatments were arranged as mainplots, and foliar treatments as subplots.
Soil applied treatments were broadcast and preplant incorporated as
K2SO4. Mainplots consisted of 20; 36-inch rows, which
extended the full length of the irrigation, run (1200 ft.). Each mainplot
area was split into two, 10 row subplots, also extending the full length of the
irrigation run. The field was planted to DPL 90 and watered-up on 12 April.
Foliar applications of KNO3 fertilizer were made at four dates
throughout the first fruiting cycle of the crop to the entire subplot areas
by use of a groundrig applicator at a carrier rate of 25 gallons per acre (Table 2). First bloom
occurred on 15 June and plots were progressing into cutout based upon nodes
above the top (first position) white flower (NAWF) and bloom counts by 19
August. The final irrigation was applied 31 August. The entire center eight
rows of each subplot were mechanically picked on 24 October from which yield
estimates were made. A preseason soil sample was taken in April 1991 to determine
the concentrations of the exchangeable cations (Table 3).
The locations of the three K fertility trials included the University
of Arizona (UA) Safford Agriculture Center (SAC, Pima clay loam), UA Maricopa
Agriculture Center (MAC, Casa Grande sandy loam), and a cooperator site located
near Coolidge, AZ on
a Mohall sandy loam soil series. Initial soil test results are given for
each location in Table 4. The exchangeable
cations including Ca, Mg, Na, and K were extracted using 1 M ammonium acetate
(pH 7), and exchangeable Zn was extracted with DTPA. Phosphate (P) was extracted
with sodium bicarbonate, and nitrate (NO3-N) was determined using an
ion-specific electrode (in a 1:1 soil:water extract). Soil pH was determined
using a glass electrode (1:1 soil-to-water ratio).
At the SAC both Upland (DPL 90) and Pima (S-6) cotton were planted 21 April and
watered-up on 23 April. Plots consisted of eight, 40-in. rows, each 34 ft. in length. Treatments included both soil and foliar K
applications. All soil K application were broadcast and preplant incorporated using K2SO4 as the K source. Four
foliar applications of KNO3 were applied over the primary fruiting
cycle, the date, HUAP, and rate of each foliar application is given in Table 5. All foliar
applications were made using a ground-rig applicator with 25 gal./acre carrier. The soil and foliar K applications were
combined to form a factorial arrangement of treatments with five replications
as shown in Table 6. The Upland and Pima
cotton had a final irrigation on 29 September and the center four rows of
each plot were mechanically picked on 18 November from which yield estimates were made.
The K fertility trial at the MAC included only foliar K applications applied
over the primary fruiting cycle to Pima cotton (S-6). Cotton was planted on
19 April (686 HU after 1 January) in plots consisting of four 40-in. rows that
were 40 ft. long. The six foliar treatments (Table 7) were arranged over the experimental
area in a RCBD with five replications. The experimental area received a final
irrigation on 28 August and the center four rows of each plot were mechanically
picked on 19 November
At Coolidge, K treatments were pre-plant, band-applied approximately 8
in. to the side of the seed row to a depth of 8 in. using two shanks per row
applicator. Plots were eight 40 in. rows wide and extended the full length
of the irrigation run (1200 ft.). The K source was K2SO4
and the rates of application are shown in Table 8.
Upland cotton (STV KC311) was planted on 14 April (512 HU after 1 January) and
treatments were applied in a RCBD with four replications. The last
irrigation was applied on 10 September prior to mechanical picking the
entire center eight rows of each plot on 29 October.
Three K fertility trials were conducted in 1993, which included the SAC, MAC, and
the Yuma Valley (Gadsden
clay loam) locations.
At the SAC, both Upland (DPL 90) and Pima (S-7) cotton
were planted 26 April (525 HU after 1 January). The experimental design was
identical to that of 1992 for the site. Three foliar applications of KNO3
were applied over the primary fruiting cycle
(Tables 9 and 10).
Both Upland and Pima cotton received a final irrigation on 2 August and the center
four rows of each plot were mechanically picked on 11 November 1993.
At MAC, the K fertility study experimental design was also identical to the
previous year for the site.
Cotton (Pima, S-7) was planted on 5 April (471 HU after 1 January). Foliar
treatment rates and dates (HUAP) are given in Table 11.
The experimental area had a final irrigation on 17 August and the center
two rows of each plot were mechanically picked on 18 October.
In the Yuma Valley, Upland (var. DPL 5409) cotton received aerial
applications (10-gal carrier/acre) of foliar-KNO3 over the
course of the growing season (Table 12). Plots were 24 (40-in.) rows
that extended the full length of the 640-ft irrigation run. Cotton was
planted and watered-up on 11 April (773 HU after 1 January) and treatments
were applied to plots
arranged in a RCBD with four replications. The final irrigation was on 15
August prior to mechanical picking of the entire center eight rows of each plot on
Two K fertility studies were undertaken in 1994. The locations included MAC and SAC.
At the MAC, the experimental
design was identical to those of the previous two years at the site. Cotton was
planted on 29 March (428 HU accumulated after January 1). Foliar treatments, rates,
and dates (HUAP) are given in Table 13. The entire center two
rows of all plots were mechanically picked on 29 October from which yield
estimates were made.
The experimental design of the K fertility trial at SAC was also identical to
those of 1992 and 1993. Pima (S-7) cotton was planted on April 7 (411 HU
accumulated after January 1) and replanted on 27 April (659 HU accumulated
after January 1) due to an irregular plant stand; and Upland (DLP 90) was
planted on 7 April (411 HU accumulated after January 1). The date, HUAP,
and the rate of each foliar application are given in Tables 14
and 15. The entire center two rows of all
plots were mechanically picked on 22 November
Three K fertility studies were conducted in 1995. The locations included
SAC, MAC and a farmer cooperator site at Buckeye, AZ on a Laveen sandy loam
soil series. The experimental design used in SAC and MAC were identical
to the three preceding years.
At the SAC, the same varieties as previous
years were planted on 4 April (389 HU accumulated after January 1) and replanted
on 26 April (581 HU accumulated after January 1) due to an irregular plant stand.
The date, HUAP, and the rate of each foliar application are given in
and 17. Plots were mechanically picked on
31 October for the Upland (DPL 90) and 29 November for the Pima (S-7) cotton.
At the MAC, cotton was planted on 4 April (517 HU accumulated after 1 January).
Foliar treatments, rates and dates (HUAP) are given in Table 18.
Plots were mechanically picked on 21 November
The Buckeye site study was conducted with a farmer-cooperator. Pima (S-7)
cotton was planted on 3 March (363 HU accumulated after 1 January) and received
one foliar K treatment in split plots that had received all combinations of soil
applied K rates (Table 19). Each plot was 8, 38 in.
rows wide with a run of 1216 ft., and was split into two 4-row subplots to accommodate
the in-season foliar treatment which was applied on 2 August. The K sources for the foliar and soil applications were KNO3 and K2SO4 respectively. The entire center two rows of all plots were harvested on 18 November.
For each site-year of the project (1991-1995), all crop inputs (irrigation, pest
control, and nitrogen (N) fertilization, etc.) were applied as needed throughout
the season. Routine plant measurements were obtained every two weeks for all
plots, including plant height, number of mainstem nodes, bloom counts, number of
nodes above the topmost white flower to the terminal (NAWF), and percent canopy
closure. Heat unit data was collected from AZMET weather stations at each location
and heat units accumulated after plant planting (HUAP) was determined using 86/55
oF maximum and minimum thresholds, respectively. Statistical analyses of
all resultant data (12 site-years) collected in this experiment were performed
in accordance to procedures outlined by the SAS Institute (1985).
Results and Discussion
There were no apparent symptoms that would indicate any K nutritional problems
at any of the 12 site-years utilized in this project. None of the plant measurements
collected in this project revealed any differences due to treatments. Fruit
retention (FR) levels were favorable for all treatments, as was the
vegetative/reproductive balance (height to node ratio, HNR) maintained by
the crop (data not shown in this report). The observed significance level
(OSL) for the soil/foliar interaction studies for all locations (Tables 1-18)
revealed no differences among K fertilization treatments for both Pima
(S-7) and Upland (DPL 90). Generally, the OSLs were about an order of
magnitude greater than an alpha value ("=0.05) commonly used for declaring
statistically significant differences in the testing of hypotheses. At the Buckeye location (Table 20), the OSL indicated a significant
difference associated with the foliar treated plots. The results indicated a
reduction in yield associated with the soil-plus-foliar treated plots which may
have resulted from an "osmotic inhibition". A high "solubility salt" such
as KNO3 that was used for the foliar application may have had
an inhibitory effect on the crop. Bolt and Bruggenwert (1976) found that soluble
salts deposited on the plant exert high osmotic pressure (e. g. in excess of 5-10
bars), which may have a detrimental effect on subsequent crop growth and development.
Foliar K applications at Buckeye in 1995 were undertaken at the time
(2 August) when plant nutrient uptake may be receding and just prior to an
irrigation event when soil and plant water levels were low. The combination
of the above factors may have been responsible for the reduction in yield of
the foliar treated plots. The OSLs (Table 19) for the soil-only and
soil-plus-foliar treated plots indicated no yield response due to K
fertilization. The results (Table 21) of
the soil samples taken at two dates at the Buckeye location revealed
that the exchangeable K for the two upper horizons at the study site was
barely higher than the minimum threshold of 150 ppm critical level currently
used in UA cotton fertility guidelines to support cotton production in Arizona soils (Silvertooth, 1998).
Also, in 1992, a physical and chemical characterization of
southern Arizona representative agricultural soils was undertaken (Table 22). The result of these
analyses (Table 22) revealed mixed
clay mineral composition (Unruh et al., 1993). None of the soils contained
less than 150-ppm exchangeable K except the Superstition soil. An important
feature of these analyses is that all soils contain K bearing mica, and none
contain significant amounts of vermiculite, which possesses a high
capacity for K fixation.
These results provide the basis for two important observations; 1) the 150
ppm soil K threshold for cotton does not appear to be too low in that yields
were not improved with K fertilization (Silvertooth, 1998); and 2) in view
of the outcome at the Buckeye study (1995), caution should be exercised in
the application of foliar fertilizers, particularly just prior to an irrigation.
The valuable technical assistance and cooperation provided by Eddie
W. Carpenter, Lee J. Clark, McD Hartman, Dan Gladden, J. S. Stephens & Sons (Paloma Ranch),
The Barkley Co. of Arizona (Yuma Valley), Prechel Farms (Coolidge), and H-4 Farms
(Buckeye) are greatly appreciated.
- Bolt, G. H., M. G. M. Bruggenwert (ed.). 1976. Soil chemistry. A. Basic elements. Elsevier Scientific Publishing Company. Amsterdam-Oxford-New York.
- Cassman, K. G. 1986. Soil, crop management factors which influence cotton potassium nutrition on vermiculitic soils of the San Joaquin Valley. J. Fert. Issues 3:38-45.
- Cassman, K. G., T. A. Kerby, B. A. Roberts, D. C. Bryant, and S. M. Brouder. 1989a. Differential response of two cotton cultivars to fertilizer and soil potassium. Agron. J. 81:870-876.
- Cassman, K. G., B. A. Roberts, T. A. Kerby, D. C. Bryant, and S. L. Higashi. 1989b. Soil potassium balance and accumulative cotton response to annual potassium additions on a vermicultitic soil. Soil Sci. Soc. Am. J. 53:805-812.
- Cassman, K. G., T. A. Kerby, B. A. Roberts, D. C. Bryant, and S. L. Higashi. 1990. Potassium nutrition effects on lint yield and fiber quality of acala cotton. Crop Sci. 30:672-677.
- Cassman, K. G., B. A. Roberts, and D. C. Bryant. 1992. Cotton response to residual fertilizer potassium on Vermiculitic soil; organic matter and sodium effects. Soil. Sci. Soc. Am. J. 56:823-830.
- Dhindsa, R. S., C. A. Beasley, and I. P. Ting. 1975. Osmoregulation in cotton fiber. Plant Physiol. 56:394-398.
- Kerby, T. A. and F. Adams. 1985. Potassium nutrition of cotton. p. 843-860. In R. D. Munson (ed.). Potassium in Agriculture. ASA, CSSA, and SSSA, Madison, WI.
- Mullins, G. L., C. H. Burmester, and D. W. Reeves. 1991. Cotton response to the deep placement of potassium on Alabama soils. p. 922-924. In D. J. Herber and D. A. Richter (ed.) Proc. Beltwide Cotton Conferences, San Antonio, TX. 8-12 1 January 1991. National Cotton Council, Memphis, TN.
- Oosterhius, D.M., W. N. Miley, R. Maples, and S. D. Wullschleger. 1991. Foliar fertilization with potassium nitrate in cotton., p. 942. In D. J. Herber and D. A. Richter (ed.) Proc. Beltwide Cotton Conferences, San Antonio, TX. 8-12 1 January 1991. National Cotton Council, Memphis, TN.
- SAS User's Guide: Statistics, 6th Edition. Cary, NC: SAS Institute Inc., 1990. p 891-996.
Silvertooth, J. C. 1998. Soil fertility and soil testing guidelines for Arizona cotton. University of Arizona Cotton Agronomy Extension Bulletin (2/98). Tucson, AZ.
- Tupper, G. R., R. R. Bridge, and M. W. Ebelhar. 1991a. Interaction of potassium rates, placement, and variety. p. 919-921. In D. J. Herber and D. A. Richter (ed.) Proc. Beltwide Cotton Conferences, San Antonio, TX. 8-12 1 January 1991. National Cotton Council, Memphis, TN.
- Tupper, G. R., M. W. Ebelhar, and H. C. Pringle III. 1991b. Potassium and nitrogen rate interactions. p. 925-927. In D. J. Herber and D. A. Richter (ed.) Proc. Beltwide Cotton Conferences, San Antonio, TX 8-12 1 January 1991. National Cotton Council, Memphis, TN.
- Unruh, B. L., J. C. Silvertooth, and D. M. Hendricks. 1994. Potassium fertility status of several Sonoran Desert soils. Soil Science, 158(6): 435-441.
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/az10068e.html
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