Vol.1, No.3, 143-147 (2010) Agricultural Sciences
doi:10.4236/as.2010.13017
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Yield enhancement of droughted wheat by film
antitranspirant application: rationale and evidence
Peter S. Kettlewell*, William L. Heath, Ian M. Haigh
Crop and Environment Research Centre, Harper Adams University College, Newport, UK; *Corresponding Author:
Received 25 August 2010; revised 28 September 2010; accepted 5 October 2010.
ABSTRACT
Extensive research in the 20th century explored
the potential for mitigation of drought by ap-
plying polymers (film antitranspirants) to leaves
to reduce water loss. It was concluded that film
antitranspirants are of limited usefulness, since
the polymers reduced photosynthesis (in addi-
tion to transpiration) and this was assumed to
be detrimental to growth and yield. We propose,
however, that irrespective of reduced assimilate
availability from photosynthesis, the most drou-
ght sensitive stage of yield formation in wheat
may respond positively to antitranspirant ap-
plication. Six field experiments involved apply-
ing the film antitranspirant di-1-p-menthene at
five development stages and 10 soil moisture
deficits (SMD) in total over three years. Yield
was reduced when the film antitranspirant was
applied at development stages less-sensitive to
drought, from inflorescence emergence to an-
thesis, consistent with the conclusions from
previous research. In contrast, yield was in-
creased when the film antitranspirant was ap-
plied at flag leaf stage, just before the stage
most sensitive to drought (boot stage). These
results show that film antitranspirant has the
potential to mitigate drought effects on yield of
wheat.
Keywords: Di-1-p-Menthene; Triticum Aestivum;
Water Deficit
1. INTRODUCTION
The majority of global food supply is from cereal
crops in rainfed agriculture, and this is highly vulnerable
to drought in many countries. An indication of grain
yield lost from drought is given by comparing rainfed
and irrigated yield: in developing countries rainfed ce-
real yield is less than half the yield of irrigated cereals
[1]. The improvement of crop water productivity (yield
per unit of water used) will be an important component
of the response to future global pressures on food supply,
such as population growth and climate change [2]. Re-
cent reviews of methods of improving crop water pro-
ductivity [1,3,4] have omitted one agronomic method:
the use of film antitranspirants to reduce water loss from
plants. This omission is understandable, since the three
main reviews of antitranspirants [5-7] and subsequently
textbooks on plant water relations and on drought man-
agement [8-10] have concluded that film antitranspirants
have very limited usefulness.
Commercially-available film antitranspirants are gen-
erally polymers sprayed as emulsions in water and in-
clude hydrocarbons, terpenoids and latex. Research into
film antitranspirants was conducted mainly from the
1950s to the 1970s, and the outcome of this work on a
range of plant species was to establish clearly that al-
though water loss from the leaf could be reduced, the
films are also of low permeability to carbon dioxide en-
tering the leaf and thus photosynthesis is restricted. A
detailed review tabulates the published effects of 23 film
antitranspirants in concurrently reducing transpiration
and photosynthesis across 13 plant species [7]. Reviews
and textbooks have therefore concluded that antitranspi-
rants are only of value for situations where photosynthe-
sis is not important but where reduction in water loss is
beneficial [5-10]. Most of these uses are on ornamental
species, e.g. on Christmas trees which have been de-
tached from the roots and where growth is not needed,
but it is desirable to reduce the needle drop resulting
from desiccation (http://www.wiltpruf.com/Home/Story/
tabid/392/Default.aspx). Film antitranspirants are not
recommended on any large-scale crops. This is not sur-
prising, taking account of the above conclusion, since
photosynthesis is clearly important as the source of as-
similate for crop yield.
The conclusion of limited usefulness is, however,
based only on a consideration of the physiology of the

P. S. Kettlewell et al. / Agricultural Sciences 1 (2010) 143-147
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
144
processes of transpiration and photosynthesis. A more-
holistic approach, embracing all aspects of crop physi-
ology, recognises that growth and yield depend on the
integration of these processes with the stage of devel-
opment of the plant. It is well-known that the sensitivity
of yield-forming processes to drought in most crops de-
pends on the development stage at which drought occurs
[11]. The most sensitive stage in wheat is just before
emergence of the inflorescence [12]. This stage is exter-
nally visible as the swollen inflorescence inside the flag
(final) leaf sheath, is referred to as the boot, booting, or
boots swollen stage, and is designated growth stage (GS)
45 on the Zadoks scale [13]. We propose that the benefit
to wheat yield of reduced loss of water from applying a
film antitranspirant at this stage may outweigh the det-
riment of the concomitant reduction in photosynthesis
leading to a net yield gain. Spraying too early or too late
would, however, be expected to reduce yield. A yield
reduction would also be expected if drought was insuffi-
ciently severe.
Six field experiments were conducted over three years
to collect preliminary evidence in support of the above
rationale for yield enhancement of droughted wheat
from film antitranspirant application. The experiments
were conducted on a low available water capacity soil
with varying reproductive development stage and soil
moisture status at application of a film antitranspirant.
The combined data from these experiments was analysed
by multiple regression to separately quantify the rela-
tionships of yield response to the antitranspirant with
development stage at application and SMD at applica-
tion. This enabled the hypothesis to be tested that film
antitranspirant can increase yield of droughted wheat if
applied at the boot stage.
2. MATERIALS AND METHODS
Winter wheat seed (cultivar Claire) was sown on 5
November 2002, 17 November 2003, and 5 November
2004 on a loamy sand soil in Flat Nook Field on the
Harper Adams University College farm (52o 46’ N, 2 o
25’ W). The available water capacity of the soil is 180
mm/m with an average soil depth little more than 1 m.
Agronomy followed typical practice for intensively-
grown wheat in the UK with herbicide, insecticide, fun-
gicide and growth regulator applications as required.
Nitrogen fertilizer applications were adjusted to take
account of soil nitrogen status in February. Two adjacent
experiments were conducted in each of the three years
with one experiment in each year exposed to rainfall and
the other experiment covered by polythene tunnels to
prevent rain reaching the root zone. Polythene tunnels
were erected between GS 37 and GS 39 (21 May 2003;
26 May 2004; 19 May 2005). Three tunnels were used,
each covering 20 × 9 m area and 3.2 m high, consisting
of galvanized steel hoops mounted on rails as described
by Beed et al. [14]. The tunnels were covered by poly-
thene except at the ends and from ground level to about
0.5 m. The tunnels were maintained in position over the
plots until harvest, and only moved for spraying the plots.
The prevailing wind is from the West and the tunnels
were orientated with the longer side East-West to maxi-
mise air flow through the tunnels and minimise tem-
perature differences from the adjacent uncovered ex-
periment. Plots were approximately 1.7 m by 10 m with
the tunnels arranged perpendicular to the plots. Anti-
transpirant treatments were arranged in a randomised
complete block design with two, six, and six blocks re-
spectively in 2002-2003, 2003-2004 and 2004-2005 for
covered plots. There were two, six and 15 blocks respec-
tively in 2002-2003, 2003-2004 and 2004-2005 for un-
covered plots. In 2002-2003 there were two replicate
plots for each treatment randomised within each block.
Weather and logistical constraints prevented antitranspi-
rant application at the boots swollen stage in every year.
Treatments were application of a film antitranspirant at
one development stage in 2002-2003, and two develop-
ment stages in 2003-2004 and in 2004-2005. Develop-
ment differences of the uncovered plots and those under
polythene tunnels were small and insufficient to allocate
a separate growth stage. Di-1-p-menthene (96%, Emer-
ald, Intracrop Limited, Lechlade UK) was sprayed on 24
June 2003 at anthesis complete (GS 69), on 24 May
2004 at flag leaf just visible (GS 37) and on 7 June 2004
at half inflorescence emerged (GS 55), on 27 May 2005
at flag leaf ligule just visible (GS 39) and on 3 June 2005
at GS 45. All sprays were in a volume of 200 litres ap-
plied through flat fan nozzles, at an application rate of 5
litres/ha in 2002-2003 and 2.5 litres/ha in 2003-2004 and
2004-2005. Control plots were unsprayed.
For the uncovered plots, SMD was calculated using
irrigation scheduling software [15] which calculated
potential evapotranspiration (PE) using a modified Pen-
man equation and accumulated a daily SMD from 1st
April by subtracting rainfall. Meteorological data for the
calculations was collected at a weather station within 1
km of the experiments. For the plots under polythene
tunnels the same PE calculation was used, but rainfall
was not subtracted after the date on which the tunnels
were erected. This model has performed well in estimat-
ing soil water measurements [15]. Plots were com-
bine-harvested in late August and yield was adjusted to
85% dry matter.
Development stage at application and SMD would be
expected to be confounded under the polythene tunnels,

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145
since the SMD accumulates progressively so that it is
likely to be greater at later development stages at appli-
cation. This might also be expected to apply to some
extent for the uncovered plots since PE tends to increase
over the spring treatment application period when air
temperature and solar radiation are increasing. This in-
herent confounding means that statistical analysis of
each separate experiment does not give clear information
on the effect of antitranspirant application at the differ-
ent development stages. Therefore the effects of devel-
opment stage at application and SMD were separately
quantified using multiple regression on the combined
data from all experiments. The yield response to the an-
titranspirant was calculated as the difference between the
means of antitranspirant and unsprayed plots for each of
the ten SMD and GS combinations. The combined yield
response data for all three years was then used as the
response variate in multiple regression analysis with two
explanatory variates: numerical values of the Zadoks
code for the development stage of the crop on the date of
spraying, and a variate calculated from the SMD in mm.
Several SMD variates were used. The mean SMD was
calculated over different periods before and after anti-
transpirant application, and also SMD on the date of
application was used. In order to test whether there was
a difference in response for uncovered or covered plots a
factor with two levels, uncovered or covered, was in-
cluded in the multiple regression analysis. GenStat soft-
ware (11th edition; VSN International Limited, Hemel
Hempstead) was used for all analyses. Since significance
tests in the multiple regression analysis were based on
relatively few degrees of freedom, the robustness of the
tests and of the estimation of the regression coefficients
was evaluated by cross-validation. The multiple regres-
sion analysis was conducted 10 times omitting data for a
different SMD and GS combination for each analysis.
3. RESULTS
The SMD at the time of antitranspirant application
varied from 118 mm to 41 mm (equivalent to 23% to
66% of available water). In 2002-2003 the SMD was
already large at the antitranspirant application, but in
2003-2004 and 2004-2005 SMD was small at the time of
the first application, although the SMD increased pro-
gressively for both uncovered and covered plots up to
and beyond the time of the second spray (data not
shown). Thus, as anticipated, the development stage at
application and the SMD were confounded in 2003-2004
and 2004-2005, with greater SMD at later development
stages. Therefore the unadjusted yield data cannot be
used to draw clear conclusions on the effects of these
two factors on the yield response to the film antitranspi-
rant. Unadjusted yield was representative of UK inten-
sively-grown winter wheat (range of control yield 6.39
t/ha to 8.92 t/ha).
The SMD variate, in combination with development
stage at the time of application, that gave the largest
percentage variance explained was the SMD at the time
of application and results are presented for this analysis
only. These two explanatory variates accounted for 60%
of the variance in yield response to the antitranspirant (P
= 0.017; 7 DF). The fitted model (yield response = 0.595
+ 0.018 SMD − 0.040 GS) enabled the yield response to
the antitranspirant to be calculated for each development
stage as if the SMD had been the same. Cross-validation
using nine GS and SMD combinations for each analysis
showed that there were only small changes to the regres-
sion parameters from removal of any one of the 10 GS
and SMD combinations, although the constant was only
significant for three of the 10 regressions. The overall
regression became marginally significant (P = 0.060) for
one of the GS and SMD combinations, but since there
were only small changes to the regression parameters it
was concluded that the multiple regression analysis was
relatively robust.
The results of the multiple regression analysis are pre-
sented as two graphs: yield response adjusted to the
mean SMD at application against development stage,
and yield response adjusted to the mean development
stage at application against SMD. Figure 1 shows that
yield was linearly related to development stage at appli-
cation and was reduced by application at GS 55 and GS
69 stages. In contrast, yield increased when antitranspi-
rant was applied at the earliest two stages tested: GS 37
and GS 39. Application at GS 45 had little effect on
yield. The inclusion of the factor testing the difference
between uncovered and covered plots was not significant
(P = 0.832), confirming that the allocation of a single GS
for both covered and uncovered plots at the time of ap-
plication was appropriate.
Multiple regression analysis also showed that, after
adjusting for development stage, yield was linearly re-
lated to the SMD at the time of spraying, with substan-
tial reductions in yield from the antitranspirant applica-
tion at low SMD, but increases in yield at high SMD
(Figure 2). Since the inclusion of a factor for uncovered
or covered plots in the multiple regression was not sig-
nificant, as described in the preceding paragraph, it was
clearly a reasonable assumption that the same PE calcu-
lation was appropriate for both environments. The fitted
model was used to calculate the threshold SMD needed
to obtain a yield increase at the most responsive stage
(GS 37). This threshold SMD is 48 mm for the cultivar
Claire on this loamy sand soil (equivalent to 27% of the
available water). The threshold SMD for an economic

P. S. Kettlewell et al. / Agricultural Sciences 1 (2010) 143-147
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
146
Figure 1. Relationship between yield response to film anti-
transpirant (adjusted for calculated SMD at application) and
development stage at application in 2003, 2004 and 2005. Fit-
ted regression model is described in the text.
Figure 2. Relationship between yield response to film anti-
transpirant (adjusted for development stage at application) and
calculated SMD at application in 2003, 2004 and 2005. Fitted
regression model is described in the text.
response will depend on the relative prices of antitran-
spirant and grain.
4. DISCUSSION
The reduction in yield from application of the film an-
titranspirant after the most drought-sensitive boot stage
was expected from the conclusions of the reviews and
textbooks on this topic, i.e., from the prevailing para-
digm. The film restricts photosynthesis and therefore
reduces the supply of assimilate available for the growth
of the developing florets/caryopses. In contrast, the in-
crease in yield from application of the film antitranspi-
rant just before boot stage is counter-intuitive in relation
to the prevailing paradigm, but supports our hypothesis.
The benefit of reducing water loss just before boot stage
must have exceeded the detriment of reducing photo-
synthesis. An application before the boot stage is pre-
sumably needed so that water stress is ameliorated in
advance of the most sensitive stage. It is possible that
application to droughted plants at an earlier stage than
flag leaf visible may prove to be even more effective.
Support for the concept that reducing water loss from
leaves with a film antitranspirant may lead to increased
yield in certain circumstances is shown by the work of
Davenport et al. [16]. They articulated a similar counter-
intuitive principle to that outlined here based on experi-
ments with oleanders. Despite a reduction in photosyn-
thesis, increased growth in size of stem internodes
through cell expansion was found following antitranspi-
rant application. Further support is found in reports of
yield enhancement from film antitranspirants applied at
or near the time of sensitive stages in other seed crops
from the early years of antitranspirant research, includ-
ing sorghum [17], rapeseed [18] and corn (maize) [19].
More-recently, such reports have been cited to cast doubt
on the conclusion in reviews and textbooks of limited
usefulness of film antitranspirants [20]. Our study has,
however, provided a further advance in knowledge by
demonstrating quantitatively that film antitranspirant
applied to a seed crop can both increase and decrease
yield depending on development stage at application and
soil moisture status, and therefore allows a simple SMD
threshold for application to be calculated. This is a par-
ticular advantage in the UK where pre-anthesis droughts
occur relatively infrequently [21]. A threshold SMD may
help agronomists and growers decide whether a spray
will be justified in a given year, analogous to current
practice with pest or disease thresholds for decision
support on insecticide or fungicide applications.
Saini and Westgate [22] reviewed the effects of
drought on reproductive development of cereals and
concluded that meiosis in the pollen mother cells during
inflorescence development is the process affected during
the sensitive boot stage. Drought at this stage leads to
pollen sterility and lower yield through reduced seed set.
Drought-induced pollen sterility has been linked to re-
duced invertase activity, which in turn appears to result
from water stress effects on transcription of genes cod-
ing for invertase [23]. No data on the mechanism by
which film antitranspirant increases yield has been col-
lected in our study, but it can be speculated that this may
have occurred through a reduction in drought-induced
pollen sterility. Further research is needed to study the
physiological effects of film antitranspirant on wheat,
especially effects on plant water status, gas exchange,
pollen development and yield components.
The frequency and severity of pre-anthesis drought is
greater in many other wheat-growing countries, e.g.
much of the USA and Australia [24], than in the UK.
The benefits from using film antitranspirant may there-
fore be greater in these countries, which produce a large
proportion of the world’s wheat supply. Furthermore,

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since the sensitivity of yield to meiotic-stage water stress
is common to other small-grain cereal species [22], the
findings reported here may be applicable to a large pro-
portion of rainfed cereal production and hence global
food supply. Indeed the findings may be applicable to
any crop relying on reproductive development for the
formation of yield. Further research is needed with a
range of species and environments to test the wider ap-
plicability of these results.
5. ACKNOWLEDGEMENTS
We are grateful to staff of the Crop and Environment Research Cen-
tre, especially D. McInnes, for technical assistance, to I. G. Grove for
discussion of soil water status measurement, and to M. C. Hare for
comments on an early version of the manuscript. I.M.H. was supported
by the Home Grown Cereals Authority, and W.L.H. was supported by
Harper Adams University College. Emerald was a gift from B. Lewis,
Intracrop Limited, Lechlade UK.
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