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Ill. Yield and Quality Responses to Chloride
PAUL E. FIXEN
some crops and cropping situations appear to have a greater potential than
others to benefit from its application.
Since the late 1970s, extensive C1- research has been conducted on
wheat and barley in the northwestern United States and the Great Plains of
North America. Many of these studies have shown beneficial effects of C1-,
and others have shown none. Factors influencing response probability
other than crop or cultivar will be discussed in Section V.
1. Cultivar Differences
It is clear that cereal crops not only differ in their potential for response
to C1- in the field (Fixen ef al., 1986b), but cultivars also differ in responsiveness. Average C1- responses across 5 site-years spanning 3 years for
three hard red spring wheat cultivars in South Dakota were 4 1 1, 330, and
7 kg grain ha-’ for “Butte,” “Marshall,” and “Guard,” respectively (Fixen,
1987). A screening of 15 cultivars at two locations resulted in response at
least at one location by 12 of the cultivars. “Guard” was again one of the
three cultivars that showed no response. Some but not all of the response
differences were explainable based on disease susceptibility.
Spring wheat cultivar differences have also been measured in Manitoba
(Mohr, 1992). Average grain yield responses to 50 kg C1- ha-’ across four
sites were 150, 137, 116, and - 16 kg ha-’ for “Biggar,” “Roblin,” “Marshall,” and “Katepwa” cultivars, respectively. “Katepwa” had also failed to
respond to C1- at eight sites in earlier studies and, like “Guard” in South
Dakota, appears to be a C1--nonresponsive cultivar.
The Cl- responsiveness of five spring barley cultivars was evaluated at
different sites for 2 years in eastern South Dakota (Gelderman ef al., 1988).
Average grain yield responses were 222, 200, 200, 49, and I 1 kg ha-’ for
“Robust,” “Hazen,” “Morex,” “Bowman,” and “Primus 11” cultivars,
respectively. Similar to spring wheat, some barley cultivars seem nonresponsive to C1- fertilization.
Similar barley cultivar differences in C1- response have been measured
in the Manitoba research referred to earlier (Mohr, 1992). Average response across four sites varied from 239 kg ha-’ for the most responsive
cultivar, “Heartland,” to -257 kg ha-’ for the least responsive cultivar,
“Bedford.” “Bedford” had responded positively at two out of eight sites in
earlier studies with an average grain yield response across all eight sites of
187 kg ha-’.
CROP RESPONSES TO CHLORIDE
Differences in CI- response of hard red winter wheat cultivars have been
measured in Kansas (Bonczkowski, 1989). In a study of “Arkan,” a cultivar moderately resistant to leaf rust, and “Newton,” a leaf rust susceptible
cultivar, a C1- by cultivar interaction was detected in 1 out of 3 years.
Grain yield responses to 50 kg C1- ha-’ were 667 and 47 kg ha-’ for the
moderately resistant and susceptible cultivars, respectively. It appeared
that the leaf rust resistance in the moderately resistant cultivar was enhanced by C1- application.
2. Magnitude and Frequency of Yield Response
The largest reported wheat or barley yield increases to CI- fertilizers have
occurred on take-all-infested winter wheat grown in the northwestern
United States on moderately acid soils. For example, nine grain yield
increases reported in several studies conducted from 1980 to 1983 ranged
from 470 to 2 150 kg ha-’, with an average of 1076 kg ha-’ (Christensen et
al., 1981; Christensen and Brett, 1985; Powelson et al., 1985; Scheyer et
al., 1987). These responses were all determined by comparing (NH4)2S0,
to a rate of NH4Cl application giving an equivalent amount of N.
Addition of KCI to soils testing very high in available K in Saskatchewan, Canada, resulted in average yield increases of 342 kg ha-’ across 6
winter wheat sites, 192 kg ha-‘ across 18 spring wheat sites, and 128 kg
ha-’ across 9 spring barley sites (Wang, 1987). Durum yields were not
increased when averaged across 3 sites. Yield response was statistically
significant at 8 of the 36 sites. Wang (1987) suggested that response may
have been due to the lower osmotic potential caused by C1- uptake and the
resulting increase in plant turgor under moisture stress.
Wheat and barley grain yield responses to CI- fertilization over five
states in the Great Plains of the United States were recently summarized by
Engel et al. ( 1 992). The summary showed that significant C1- response
occurred in 42% of the 169 episodes over a wide range of environments
and yield potentials (Fig. 3). It is important to note that this summary
includes cultivars such as “Guard” spring wheat, “Primus 11” barley, and
“Newton” winter wheat, which are proved nonresponding or limitedresponding cultivars. Also included are sites testing high in soil C1-.
Responses in the Great Plains have generally been modest compared to
those measured in the northwestern United States (Engel et af.,1992). The
average significant response in Engel’s summary was 304 kg ha-’ whereas
the average response for all sites was 1 I7 kg ha-’. The average response for
all sites in the Saskatchewan studies ( Wang, 1987)was 184 kg ha-’. Thus it
is economically beneficial to be able to predict responsive situations. That
will be the topic of a later discussion in this review.
PAUL E. FIXEN
Control yield, kg/ha
Figure 3. Chloride yield response relative to control yields in the Great Plains. 0,
Nonsignificant; 0, significant (>67 kg ha-'). Each data point represents a cultivar X site X
year episode (Engel et a/.. 1992).
3. Mechanisms Involved in Yield Responses
Many of the responses summarized above were due to documented
suppression of root or foliar diseases or enhancement of host tolerance to
diseases, as discussed earlier. However, in many other cases responses
could not be attributed to disease effects (Bonczkowski, 1989; Engel and
Mathre, 1988; Engel and Grey, 1991; Fixen, 1987; Fixen et al., 1986b;
Goos et al., 1989; Mohr, 1992).
The nondisease mechanisms involved in these responses have not been
clearly demonstrated. However, possible mechanisms include effects of Clon plant development and resulting stress avoidance as well as potential
effects on plant water relationships. These were discussed earlier.
4. Quality Effects
Great Plains studies have demonstrated frequent improvements in
wheat and barley quality due to CI- application. Parameters influenced
include kernel weight, plumpness or volume, and test weight (Cholick ef
al., 1986; Engel and Mathre, 1988; Engel ef al., 1992; Mohr, 1992; Schumacher, 1990; Windels et a!., 1992). In some cases quality effects, espe-
CROP RESPONSES TO CHLORIDE
cially kernel weight, have been more common than yield effects. In North
Dakota studies, barley kernel volume was increased in 6 out of 13 siteyears by application of KCl in situations wherein response to K+ was very
unlikely (Zubriski ef al., 1970). It has been observed in South Dakota that
CI- application can reduce the severity of late-season lodging in spring
wheat. Lodging reduction could be one mechanism for improvement of
Oat responsiveness to broadcast application of 187 kg KCl ha-’ was
compared to that in spring wheat and barley at 6 site-years in eastern South
Dakota (Fixen et al., 1986b).Wheat and barley responded significantly at 4
and 3 sites, respectively, but no oat responses were detected. Soil and plant
analysis as well as studies conducted the followingyear at nearby sites using
KNO, and CaCI, all indicated that responses were due to the C1- in the
KCI fertilizer. The authors concluded that oat was less responsive to C1than was wheat or barley but cautioned that the results could have been
influenced by the specific cultivars used for each species.
More intensive studies on the effects of C1- on oat cultivars were conducted by Gaspar (1988). The average grain yield responses to 64 kg CIha-’ across 5 site-years in eastern South Dakota were 160, 140, 110, 10
(nonsignificant, NS), and -40 (NS) kg ha-’ for the cultivars “Moore,”
“Benson,” “Ogle,” “Lancer,” and “Froker,” respectively. Yield responses
were due to increases in kernel weight. Neither the number of tillers nor
seeds per tiller were influenced by CI-. Parameters unaffected by CI- were
crown rust (Puccinia coronafa) infection, leaf relative water content, leaf
water potential, and stomata1 conductance.
Adjacent experiments evaluating the interaction of N and CI- showed a
slight reduction in crown rust infection from C1- at all 5 site-years and a
reduction in lodging in most cases, especially at high N rates (Gaspar,
1988). The reduction in crown rust was only 1% of the leaf area and was
considered agronomically unimportant. Solute potential and solute potential adjusted for full turgor were decreased by C1- addition, although the
decreases did not seem related to yield.
Published accounts of CI- effects on corn date back at least to 1958
(Younts and Musgrdve, 1958b).In field and pot experiments in New York,
PAUL E. FIXEN
increasing KCl rates decreased stalk rot incidence of corn whereas increasing K2S04or KP03 application had little or no effect.
Later studies in Wisconsin by Martens and Amy (1967a,b) showed that
both KCl and NH4Cl decreased pith levels of reducing sugars, decreased
natural root necrosis, and delayed death of corn plants, but increased stalk
rot when the stalks were inoculated with Diplodiu muydis (Berk). The
observation of delayed plant death is consistent with the findings of Younts
and Musgrave (1958b) that KCI reduced natural stalk rot. However, Martens and Amy ( 1967b) attributed the reduction to both K and C1, because
the effects of KC1 were much greater than the effects of NH,Cl.
The increased stalk rot in inoculated plants due to C1- application
reported by Martens and Amy (1967b) was thought to be due to the direct
injection into the stalk, which bypasses the normal advance of the pathogen from the roots. The researchers proposed that fungal growth in the root
and its advance into the stalk is delayed by both K+ and C1-, but subsequent growth in the stalk is more rapid.
Field studies in Wisconsin by Liebhardt and Munson ( 1976) evaluated
the effects of K+ and C1- on corn lodging where no KCI had been applied
for the previous 4 years. Potassium application resulted in an I800 kg ha-'
increase in grain yield and a reduction in corn lodging of 4896, whereas C1application had no effect on either yield or lodging.
Lack of significant yield response to C1- by corn was also measured in
South Dakota studies (Schumacher and Fixen, 1989). Broadcast-incorporated rates of C1- up to 5 10 kg ha-' failed to give significant yield response
for the year of application or the 2 years following the application year.
Grain moisture at harvest was significantly increased by C1- during the
third year. In the same study, spring wheat yields were significantly increased for the first 2 years.
Banding Cl--containing fertilizers near the corn row at rates higher than
those normally used has reduced grain yield and delayed maturity. Corn
growth in New York was delayed if KCI was applied in a band located
7.5 cm beside and 2.5 cm below the seed at C1- rates exceeding 50 to
100 kg ha-' (Younts and Musgrave, 1958a).Jackson el ul. ( 1 966) observed
reduced sweet corn growth and vigor following C1- application on a poorly
drained acid soil that contained Mn concretions in the Willamette Valley
of Oregon. The negative effect of C1- was attributed to an increase in Mn
availability and resulting Mn toxicity.
Research in Ohio showed no effect of NH4Cl applied in a band located
4 cm to the side and 4 cm below the seed at rates up to 100 kg ha-' (Teater
ef ul., 1960). A rate of I35 kg C1- ha-' decreased yields below those when
an equivalent amount of N was applied, but from non-C1- sources, in one
of two years. Broadcast application avoids these negative effects of C1- on
CROP RESPONSES TO CHLORIDE
corn even at much higher rates of 500 to 600 kg ha-' (Schumacher and
Fixen, 1989; Teater ef al., 1960).
Studies in the greenhouse and field were conducted on poorly drained
Atlantic coastal soils to determine if C1- toxicity could be a problem for
corn (Parker ef al., 1985). No detrimental effects were measured even at
the highest rates in the studies (728 mg C1- kg-' soil in the greenhouse and
340 kg CI- ha-' in the field).
Studies evaluating the interaction between N and K sources suggest that
C1- increases the yield response of corn to enhanced ammonium nutrition
(Dibb and Welch, 1976; Teyker et al., 1992). In a 2-year field study Teyker
ef al. (1992) found no response to enhanced ammonium nutrition with
KHCO, or K2S04 as K sources, although grain yield was increased by 380
to 560 kg ha-' when KCI was used. A greenhouse study by Dibb and
Welch ( I 976) showed that the importance of KCI supplementation increased substantially when corn was grown with ammonium nutrition.
Teyker et al. (1992) suggest that the apparent higher CI- requirement
under enhanced ammonium nutrition compared to nitrate nutrition is
perhaps due the role of C1- as a counterbalancing ion and major osmolyte.
Although corn yield increases from C1- have been measured, there
appears to be less potential for corn to benefit from CI- application in the
field than is the case for cereal crops. When positive responses occur they
have been limited in magnitude.
Although data are limited, soybean and soybean diseases do not appear
to be responsive to application of CI- fertilizer. Studies in Missouri exploring the potential of CI- in KCI fertilizer for reducing soybean cyst nematode damage or cyst counts in the soil showed no reductions (Hanson ef
al., 1988). Likewise, Kansas experiments on the effects of K and CI- on
charcoal rot severity showed a lack of treatment effects (Granade et al.,
The major concern with CI- and soybeans is the potential for toxicity in
sensitive cultivars when grown in high CI- environments that accumulate
soluble salts. Considerable research has been camed out on this problem
on the poorly drained soils of the Atlantic Coast Flatwoods area of Georgia
(Parker and Gaines, 1987; Parker et al., 1986a,b, 1987).
The major cause of the problem is a water table that remains within I or
2 m of the surface and the fact that soil moisture is lost primarily by
evaporation and transpiration, which leaves CI- in the rooting zone. The
PAUL E. FIXEN
sandy texture and high K fertilizer requirements of the soils in the region
amplify the problem, which is worse in dry years than in wet years.
Dramatic differences in sensitivity to C1- toxicity exists among soybean
cultivars, with the sensitive cultivars being C1- accumulators and the tolerant cultivars being CI- excluders. Leaf scorch due to toxicity is just detectable at leaf concentrations of 8600 mg kg-' or seed C1- concentrations of
18,100 mg kg-l (Parker et af., 1986b). Growers have solved the problem by
use of Cl--tolerant cultivars.
Reduction in tuber specific gravity by CI-, especially when applied in
bands, has been a major issue in potato production (Berger ef af., 1961).
For this reason sulfate sources have often been the preferred form of K in
Recent pot experiments have demonstrated that application of KCI as
compared to K2S0, delayed tuber development, increased plant turgor
pressure, and enhanced shoot growth (Beringer et af., 1990). These effects
suggested a less competitive shoot sink for K,SO,-treated plants and somewhat greater assimilate translocation to tubers.
Chloride application can also have beneficial effects on potato production. Oregon research has shown reductions in hollow heart with KCl
compared to K2S04and accompanying increases in yield and grade (Jackson and McBride, 1986). This research also revealed that a french fry
evaluation of tubers from experiments across 3 years showed that application of CI- did not affect uniformity of color or apparent "sugar ends."
Other studies have demonstrated reduction in frost damage in plots receiving 225 kg KCl ha-', presumably due to the 50,000 to 70,000 mg kg-l Cllevels in plant tissues (Jackson et af., 1982).
The role of CI- application in potato culture is likely dependent on a
number of factors, including end use of the tubers, disease pressures and
other stresses, and rate of K needed. Local research and experience on the
magnitude of the various potential effects of C1- need to be considered.
Soils high in C1- have reportedly produced better quality flax (Linum
usitatissimum L.) (Brioux and Jouis, 1938). Recent studies with five flax
cultivars resulted in a significant seed yield increase of 157 kg ha-' for one
cultivar and significant yield decreases of 119 and 144 kg ha-' for two
other cultivars from broadcast application of 135 kg KCl ha-' (Grady et
al., 1988). No consistent yield effects were measured during the second
CROP RESPONSES TO CHLORIDE
year of the study. However, oil content was increased from 408 g kg-I for
the control to 4 12 g kg-I for the CI- treatments. Disease incidence was very
low for both years.
High soil nitrate levels late in the season reduce the concentration of
recoverable sugar in sugar beets (Beta vufgaris L.). The uptake antagonism
sometimes observed between CI- and nitrate offers a possible mechanism
for reducing the negative effect of high nitrate on recoverable sugar in beets
(Ludwick et al., 1980). Research in Washington has shown that C1- inhibition of nitrate uptake in sugar beets can lead to increased beet sugar
percentages (James ef af., 1970a). Colorado research showed no effect of
CI- fertilization on sugar concentration of irrigated beets; however, C1available to the crop from the soil and imgation water varied from 930 to
3810 kg ha-' for the sites used (Ludwick et al., 1980).
Sugar beets accumulate large quantities of C1- and uptake has been
highly correlated with soil C1- to a depth of 120 cm. In research conducted
in the Red River Valley of central North America, C1- uptake varied
among five sites and five N rates from 28 to 226 kg ha-' and 5 to 23 kg
ha-' for tops and roots, respectively (Moraghan, 1987). Chloride uptake
generally increased as fertilizer N rate increased. Moraghan pointed out
that the redistribution of soil C1- from below 60 cm to the surface soil by
the beet tops could influence the C1- relationships of subsequently planted
Coconut and oil palms have responded markedly to C1- fertilization on
low-C1- soils, typically occurring at distances greater than 20 to 25 km
from the sea (Ollagnier and Olivin, 1984; Ollagnier and Wahyuni, 1984;
von Uexkull and Sanders, 1986). Nut yield increases as high as 50% have
been measured. Optimum tissue C1- levels of 6000 to 7000 mg kg-l have
IV. CHLORIDE SOURCES, LOSSES, AND APPLICATION
The only form of chlorine found in nature is C1-. Although other
oxidation states are possible and are important in some industrial processes, they are all unstable in the environment.
Four basic factors determine the amount of C1- available to crops growing in well-drained soils (Goos, 1987). They are (1) soil solution C1-, (2)
exchangeable C1- in the soil, (3) atmospheric deposition of C1-, including
irrigation water, and (4) fertilizer or manure C1-.
PAUL E. FIXEN
Due to the high solubility of C1- salts, most soil C1- is found in the soil
solution. Although some soil minerals contain very small amounts of C1-,
they generally do not contribute significantly to plant nutrition. Several
studies demonstrating high correlations between soil solution C1- and C1uptake by crops will be discussed later. Acid soils with clay mineralogy
dominated by 1 : 1 clays and oxides may have significant anion-exchange
capacity. Significant C1- can be held in anion-exchange sites in such soils
(von Uexkull, 1990).
Atmospheric deposition of Cl- varies greatly with geographic location.
Precipitation near ocean shores can annually contribute as much as 100 kg
CI- ha-' and drop to 20 kg ha-* just 200 km inland (von Uexkull and
Sanders, 1986). Atmospheric contribution in the midwestern United States
and Great Plains has been reported as being only 0.6 to 1.2 kg C1- ha-' per
year (Junge, 1963). Atmospheric inputs often increase near heavily industrialized areas where large quantities of coal are burned. Some imgation
waters contribute substantial C1- to crops (Fixen el al., 1986c) whereas
others contribute very little.
Chloride in the soil parent material, in precipitation, in soil drainage,
historical crop removal, and C1- applied in animal manure or fertilizers all
influence the quantity of C1- found in a particular soil. In North Dakota,
C1- levels are often high in soils derived from marine geological deposits, in
saline soils, where a shallow water table exists, and in low spots below long
slopes (Richardson et al., 1988).
The mobility of C1- in soils makes leaching the primary mode of C1- loss
(Schumacher and Fixen, 1989). As with any solute, actual leaching loss in
individual years is dependent on several interacting factors. Therefore,
persistence of C1- from fertilizer applications is difficult to predict except in
Crop removal of C1- when only grain is harvested is typically very low
and has been reported as low as 0.05% of the dry matter in wheat grain
(Knowles and Watkin, 1931). Green forage, however, can remove substantial quantities of C1-, especially when growth occurs in a high-C1environment. At peak accumulation, spring wheat contained 18 and 6 1 kg
C1- ha-' on sites testing low and high in CI-, respectively (Schumacher,
1988). By crop maturity, C1- in the aboveground portion of the plant had
dropped to 50 and 43% of these values, respectively.
Fertilizer source comparisons have indicated that all common C1sources are equally effective (Fixen ef al., 1986b; Mohr, 1992). Common