The Effect of Chloride Fertilizers on Yield
and Disease Progress in Texas Wheat
Travis D. Miller1
Introduction
Chloride (Cl) bearing fertilizers have been widely used in crop production for numerous
years, but primarily Cl has been applied as a salt associated with K, with little specific
recognition of the potential of Cl as an essential nutrient. Research over the last 30 years has
documented response of several crops including wheat, potatoes (Jackson & McBride, 1984), oil
and coconut palms (Uexkull and Sanders, 1984), barley (Goos, 1984), sugarbeet (Baumeister,
1954), tomatoes and cotton (Tisdale et al., 1985) to applied chloride. Much research on chloride
has also dealt with toxicity issues rather than nutrient responses (Eaton, 1965 and Parker et al.,
1984). Regions where a favorable Cl response has been documented are typically inland far
enough to reduce Cl deposition in rainfall, and in soils which are high in native K so that Cl
requirements have not been met with KCl fertilizer applications.
Chloride appears to be beneficial to the culture of wheat for several reasons. Chloride is
an anion required in evolution of oxygen in photosynthesis, it has a major role in ion transport or
movement of nutrients from the soil solution into the cellular solution and movement between
cells, as well as being a significant ion in maintaining turgor, or preventing wilting. There is
considerable evidence that ammonium N in a plentiful supply is beneficial to growth of the
wheat plant as well as creating an unfavorable environment for take-all, a serious disease of
wheat over much of the U.S. Chloride has been documented as a nitrification inhibitor
(Christensen et al., 1984), particularly in moderately acid soils. The inhibition of nitrification is
functional in reducing N loss to leaching or denitrification, and in preserving a favorable
ammonium to nitrate ratio which appears to be critical in management of take-all. Studies also
suggest that an increased negative osmotic potential in the plant associated with the Cl ion gives
added protection against take-all infection over that associated with ammonium fertilizers in the
absence of enhanced Cl levels (Macs, 1984).
Chloride fertilizers have also reduced infestation and delayed the onset and severity of
leaf rust (Wiese, 1987), septoria leaf blotch (Becton, 1984), tan spot (Sanders et al., 1991), stripe
rust (Scheyer et al., 1987), and common root rot (Windels et al., 1992) in certain environments.
Response to applied Cl remains unpredictable. No adequate explanation has been presented
relative to why there is a cultivar by chloride fertility interaction, or of variable response to
applied Cl in similar environments.
Texas has a diverse climate for wheat production, with wheat-fallow wheat produced
dryland in the west with under 15 inch annual rainfall to soft red winter wheat in east Texas
grown in more than 50 inch annual rainfall. The major eastern wheat producing region in eastern
1
Dr. Miller is Professor and Extension Agronomist-Small Grains and Soybeans, Soil and Crop Sciences
Department, Texas A&M University, College Station, Texas 77843-2474.
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1994 Intensive Wheat Management Conference Proceedings
Texas is the blackland prairie, a region of montmorillonitic, or high shrink-swell clay textured
soils which have an average rainfall of 30 to 40 inches per year. These soils are typically high pH
(7.5 to 8.2) and high in native K.
As a result of high native K concentration, supplemental fertility with KCl is rare. Mild
winters with frequent dew, fog and light rain create an environment favorable for the
proliferation of fungal diseases of wheat such as leaf rust, septoria leaf blotch, powdery mildew
and foot rots. The frequent winter rains also tend to leach mobile anions such as N03- or Cl- from
the surface of the soil profile, and in fields with poor internal or surface drainage, anaerobic
conditions resulting in denitrification can result.
Given conditions that would result in a high probability for response to applied Cl, field
trials were established in winter wheat in the blackland prairie over 3 crop years (1991, 1992,
and 1993). The objective of the studies changed somewhat, and additional treatments were
added as the potential for economic response to chloride bearing fertilizers was realized. In the
first year of the study, a plot was designed to identify a response-no response to Cl application.
The second year study evaluated Cl time of application and fertilizer source. Following a
substantial response to spring applied Cl in the 1991-92 crop, five studies were initiated in the
1992-93 crop to evaluate rate, time of application, source of Cl, and to compare soil and foliar
applications. Rainfall during winter and spring months was somewhat above average during
each of the three study years.
Chloride Response
In the 1991 study, 2 rates of Cl-, 14 and 29 lb/ac were compared as KCl and NH4Cl. In
this study, disease pressure was light, but there was a visually apparent difference in levels of
suppression of septoria leaf blotch between Cl topdressed wheat and wheat only topdressed with
N. Cl treated wheat trended towards higher yield (Table 1) than N treated and untreated wheat,
but differences were not statistically significant.
Table 1.
The effect of chloride fertilizer on grain yield in winter wheat. Whitewright,
TX. 1991.
Rate, ClSource
Yield, bu/ac
lbs/ac
14
KCl
34.4
29
KCl
35.1
29
NH4Cl
31.6
0
30.9
NSD
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1994 Intensive Wheat Management Conference Proceedings
With foliar fungal diseases playing such a major role in the success or failure of the north Texas
wheat crop, studies were repeated in 1991-92, based upon the encouragement offered in the
suppression of septoria leaf blotch. As luck would have it, septoria was not present in
economically damaging levels in the site selected in 1992. Leaf rust, however, became visually
apparent soon after jointing. The infestation had essentially destroyed flag leaves by mid-grain
fill. In this environment, Cl- treated wheat was easily distinguished from checks topdressed only
with ammonium nitrate (Table 2). Cl- bearing fertilizers had been applied preplant and as a
topdress at jointing. During grainfill, rather striking differences were apparent. Cl treated wheat
exhibited a more robust, upright leaf, darker green color, and substantially lower leaf rust ratings
at bloom than treatments not including Cl (Table 2). There were major differences between fall
applied treatments and topdress treatments, with Cl effects much more pronounced on spring
treatments than fall treatments.
During the progress of infection, leaf rust displays varying symptomology. It is not
uncommon in the Central and North Texas environment for a general chlorosis of leaf tissue to
be associated with leaf rust infection. In these cases, the chlorosis on wheat leaves appears to
assume a somewhat greater area relative to the leaf surface than that which is associated with
uredia, or pustules of the leaf rust organism. It has generally been assumed by wheat workers in
the region that the chlorosis is associated with the rust organism, and it indeed can be diminished
by the appropriate use of foliar fungicides. Chloride treatments in the 1991-92 Bosque county
test greatly diminished the chlorosis apparent on the leaf surface as well as erumpent uredia. The
effect of Cl on leaf rust varied greatly with time of application. Fall treatments had considerably
higher levels of infection than plots receiving spring treatments, although they exhibited less
injury from rust than the untreated check, which was topdressed only with ammonium nitrate.
The disparity between fall and spring applied Cl was also observed in grain test weight,
with spring applied treatments averaging 2 lbs/bu better than fall treatments, which were not
different in test weight than the untreated check. Yield of fall treatments and the spring applied
Cl were numerically higher than the untreated check, while spring applied NH4Cl yielded 14
bu/ac better than the check, and significantly higher than all other treatments.
Five sites were used to evaluate Cl response in the 1992-93 crop. In addition to timing
and fertilizer source, one study evaluated the potential for use of foliar solutions containing Cl,
as a high percentage of topdress N is applied to wheat as a solution. Topdress applications were
applied on March 8 at early jointing.
Results were essentially the same with respect to Cl time of application as in the 1992
study. Of five sites treated, significant Cl yield responses to spring applied Cl were documented
in 2 locations (Table 3). Yield increases with the best treatment at these sites averaged 12.1 bu/ac
greater than no Cl- check plots, or a 36% increase in yield. In the remaining 3 sites, yield was not
significantly different due to Cl- treatments, although a numerical trend suggested a response to
Cl- at 2 sites. An average across 5 sites comparing yield of spring applied Cl treatments in the
form of KCl and NH4Cl to a non-Cl- check was 41.2, 42.5 and 36.2 bu/ac, respectively. No yield
response was noted at any site to preplant Cl- applications.
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1994 Intensive Wheat Management Conference Proceedings
Table 2.
The effect of chloride fertilizer on grain yield, yield components, and plant
growth characteristics in winter wheat. Meridian, TX. 1992.
Source
Rate, lbs
Timing
Leaf Rust, %
Test Wt.
Yield,
Cl per acre
May 5
lbs/bu
bu/ac
NH4Cl
40
Spring
5
60.0 a
68.3 a
NH4Cl
40
Fall
45
58.0
59.6 b
KCl
40
Spring
30
60.0 a
58.8b
KCl
40
Fall
45
58.5 b
57.6 b
Check
0
-80
58.0 b
54.3 b
†
Means followed by the same letter are not significantly different according to the Duncan's
MRT at the 95 percent confidence level.
Wheat responded well to foliar application of Cl as NH4Cl or MgCl2. The 20 and 40
pound per acre rate of Cl as foliar NH4CI and the 40 pound per acre rate of Cl as MgCl2 were
not different from the yield achieved with soil applied KCl and NH4Cl, and were significantly
greater than the non-Cl- check. Some phytotoxicity was noted with foliar CI applications, but
wheat grew well after application, and no difference in plant size or biomass was noted at
harvest due to leaf injury at Feekes 6.0.
Cl' Tissue Concentration
CI concentrations in plant tissues are relatively high, typically ranging from 2,000 to
20,000 ppm (Maas, 1984), which is typical of the range of most macronutrients. (Johnson et al)
reported that severely deficient plants contain only 35 to 70 ppm. Reduction in yields due to
toxicity are frequently associated with tissue levels of 0.5 to 2.0% in sensitive crops and 4.0 %
or greater in tolerant crops (Reisenauer et al., 1973). In four Texas studies, whole plant samples
taken near bloom, wheat contained 1,400 to 1,700 ppm in non-Cl checks. CI tissue levels were
elevated to range from 2,700 to 4,000 ppm by fall Cl applications, whereas topdress Cl
applications near Feekes stage 6 elevated tissue concentrations to a range of 4,000 to 8,200 ppm.
As yields appeared to be related to tissue Cl levels at bloom, simple linear regression equations
were run between Cl concentration and grain yield. Equations in Table 4 describe the
relationship between tissue Cl at 3 sites over 2 years.
Figure 1 depicts the regression lines and data points associated with these lines.
Equations of the regression lines are described in Table 4. This data suggests that the base levels
of Cl found in wheat not treated with are adequate to produce average yields for the region, but
enhanced Cl levels through topdress applications can result in significant yield increases. Yield
increases appear to be related to a micronutrient response, and in some cases a micronutrient
response coupled with less injury from prevalent fungal diseases.
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1994 Intensive Wheat Management Conference Proceedings
Table 3.
Wheat grain yields as affected by chloride treatments at 5 locations in the Texas
Blacklands. 1992-1993.
Treatment
How
Rate, Cl
Time of
Wheat Yield, bu/ac‡
Applied†
lbs/ac
Appl.
Bell
Bosque
Coryell
Hill
Hamilton
KCI
G
40
Fall
43.4 a
31.2 a
29.4 c
KCI
G
40
Spring
43.9 a
45.4 ab
34.6 a
35.7 b
46.3 a
NH4Cl
G
40
Fall
44.6 a
34.7 a
28.6 c
NH4CI
G
40
Spring
44.4 a
47.7 a
31.8 a
42.4 a
46.0 a
NH4CI
F
40
Spring
45.0 abc
NH4Cl
F
20
Spring
43.7 abc
MgC12
F
40
Spring
44.0 abc
MgC12
F
20
Spring
40.5 bcd
MgC12
F
10
Spring
38.4 cd
NH4Cl
G
80
Spring
46.4 a
42.2 a
Check
---41.7 a
36.1 d
27.7 a
29.9 c
45.9 a
†G = Granular, F = Foliar
‡ Means followed by the same letter are not significantly different at the 95% confidence level according to
the Duncan's Multiple Range Test
Table 4. Regression equations describing the relationship of tissue Cl and wheat yield.
Location
Year
Equation†
Bell Co.
1993
Yield = .00068 X +40.9*
Bosque Co.
1992
Yield = .0024 X +50.1*
Bosque Co.
1993
Yield = .0018 X +33.9**
†X is equal to whole tissue Cl concentration at bloom.
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1994 Intensive Wheat Management Conference Proceedings
Acknowledgements
Much of the funding for Texas research described in this test was contributed by the
Texas Wheat Producers Board and the Phosphate and Potash Institute Foundation for
Agronomic Research. Gratitude is expressed to David Winkler, James Davis, Bill Buxkemper,
Gary Bomar, Danny Phillips and Donald Kelm; Texas county extension agents whose
contributions made these studies possible.
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1994 Intensive Wheat Management Conference Proceedings
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