Vol.2, No.3, 220-237 (2011)
doi:10.4236/as.2011.23031
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Scienc es
Cropping frequency and N fertilizer effects on soil water
distribution from spring to fall in the semiarid Canadian
prairies
R. de Jong1*, C. A. Campbell1, R. P. Zentner2, P. Basnyat2, B. Grant1, R. Desjardins1
1Eastern Cereal and Oilseed Research Centre, Central Experimental Farm, Agriculture and Agri-Food Canada, Ottawa, Canada;
*Corresponding Author: dejongr@agr.gc.ca
2Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada, Swift Current, Canada.
Received 26 May 2011; revised 24 June 2011; accepted 25 July 2011.
ABSTRACT
In the semiarid Canadian prairies, water is the
most limiting and nitrogen (N) the second most
limiting factor influencing spring wheat (Triti-
cum aestivum L.) production. The efficiency of
water- and nitro gen use need s to be asses sed in
order to maintain this production system. The
effects of cropping frequency and N fertilization
on trends in soil water distribution and water
use were quantified for an 18-yr (1967-1984)
field experiment conducted on a medium tex-
tured Orthic Brown Chernozem (Aridic Haplo-
boroll) in southwestern Saskatchewan, Canada.
Soil water contents were measured eight times
each year and plant samples were taken at five
phenological growth stages. The treatments
studied were continuous wheat (Cont W),
summer fallow - wheat, F-(W) and summer fal-
low - wheat - wheat, F-W-(W) each receiving
recommended rates of N and phosphorus (P)
fertilizer, and (F)-W-W and (Cont W) each re-
ceiving only P fertilizer, with the examined rota-
tion phase shown in parentheses. Soil water
conserved under fallow during the summer
months averaged 25 mm in the root zone, and
was related to the initial water content of the soil,
the amount of precipitation received, its distri-
bution over time, and potential evapotranspira-
tion. Under a wheat crop grown on fallow, soil
water contents between spring and the five-leaf
stage remained relatively constant at about 250
mm, but those under a stubble crop, with 40 mm
lower spring soil water reserves, increased
slightly until about the three-leaf stage. During
the period of expansive crop growth (from the
five-leaf to the soft dough stage) soil water was
rapidly lost from all cropped phases at rates of
1.87 mm·day–1 for F-(W) ( N+P), 1.23 mm· day –1 for
Cont W (N+P) and 1.17 m m·day –1 for Con t W (+P).
The initial loss was from the 0 - 0.3 m depth, but
during the la tter half of the gr o wing season from
deeper depths, although rarely from the 0.9 - 1.2
m depth. In very dry years (e.g., 1973, with 87
mm precipitation between spring and fall)
summer fallow treatments lost water. In wet
years with poor precipitation distribution (e.g.,
1970, with 287 mm precipitation between spring
and fall but 142 mm of this in one week between
the three- and five-leaf stages) even cropped
treatments showed evidence of leaching. The
above-ground biomass water use efficiency for
Cont W was 19.2 and 16.7 kg·ha–1·mm–1, respec-
tively, for crops receiving (N+P) and P fertilizer
only. Grain yield water use efficiency (8.91
kg·ha–1·mm–1) was not significantly influenced
by cropping frequency or N fertilizer. The 18
years of detailed measurements of plant and
soil parameters under various crop manage-
ment systems provide an invaluable source of
information for developing and testing simula-
tion models.
Keywords: Fallow Frequency; Water Use; Plant
Biomass; Spring Wheat; Soil Water
1. INTRODUCTION
In the semiarid region of the northern Great Plains
(i.e., the Brown Chernozemic soil zone), water is the
main factor influencing wheat (Triticum aestivum L.)
production [1,2]. Potential evapotranspiration (PET)
always exceeds precipitation (PPT) during the growing
season, and consequently farmers in this area often prac-
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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221221
tice summer fallowing (F) to conserve water for the next
crop. This practice also serves to control weeds and to
increase mineral nitrogen (N) in the soil, thereby helping
to alleviate the second greatest restriction to production
in this region (i.e., soil N deficiency) [1]. Although the
area devoted to summer fallow on the Canadian prairies
has been decreasing steadily in recent years, the rate of
decrease is lowest in the Brown soil zone (1.3% yr–1) [3];
thus, summer fallowing is still an important management
tool in this region.
The efficiency of soil water storage from precipitation
in the prairies is generally low and varies greatly de-
pending on soil texture, type of cultural practice, the
amount of crop residues left standing to trap snow, and
the amount and distribution of precipitation received in
the non-crop-growing period [4,5]. We recently assessed
the effects of cropping frequency and N fertilization on
soil water conservation based on the results from a 40-yr
experiment conducted on a medium-textured Orthic Brown
Chernozem (Aridic Haploboroll) at Swift Current, Sas-
katchewan [6]. We examined three treatments: continu-
ous wheat (Cont W) and fallow-wheat (F-W) each re-
ceiving N and phosphorus (P) fertilizer, and Cont W
receiving only P fertilizer. The results showed that at
harvest, F-W and Cont W (N+P) had similar amounts of
water in the soil profile, but Cont W (+P) had more be-
cause of less growth and reduced water use. However by
the following spring, soil water recharge, being propor-
tional to the amount of crop residues produced, had
conserved an extra 64, 55 and 40 mm of water in treat-
ments F-W, Cont W (N+P) and Cont W (+P), respec-
tively [6].
Numerous studies (see review articles [7,8]) have
been conducted in which the relationships between crop
yield and water use on the prairies have been assessed.
The effects of fertilization rates [9-11], tillage practices
[12-14], cropping frequency [15,16] and soil- and weather-
conditions [17] on water use efficiency have been docu-
mented extensively. However, less is known about the
seasonal changes in crop water use and in water use effi-
ciency of the plant biomass.
Agro-ecosystem models are being increasingly used
for site specific analyses and the development of site
adapted agricultural production systems [18,19]. On a
regional and/or national scale these models are used for
the evaluation of current land use and potential remedia-
tion measures through scenario simulations [20-22].
However, testing and validation of the models should be
done using independently measured data from field ex-
periments such as those described in this manuscript.
During the first 18 years (1967-1984) of the Swift Cur-
rent long-term crop rotation experiment, detailed meas-
urements of soil water and plant biomass were made,
with eight samplings between spring and fall on selected
treatments. Although some assessments of these data
were made [23,24], seasonal changes in soil water con-
tent and its distribution within the profile were not ex-
amined.
The objectives of this paper were to determine the ef-
fect of cropping frequency and N fertilizer on 1) soil
water trends and its depth distribution from spring to fall,
and to assess how these patterns were influenced by
weather conditions, and 2) the efficiency of water use to
produce above-ground biomass and grain of spring
wheat. Furthermore, we want to alert agricultural system
modellers to the unique nature of these long term ex-
perimental results.
2. MATERIALS AND METHODS
The Swift Current crop rotation experiment was initi-
ated in 1967 on a flat (slope < 2%) Swinton loam [25],
an Orthic Brown Chernozem [26]. Swift Current (50˚17
N, 107˚48 W, elevation 883 m) is located in the driest
portion of the Canadian Prairies, with long cold winters
and short growing seasons [27]. The soils are frozen
from mid October until March/April. Rainfall is mar-
ginal for many agricultural activities (on average 197
mm is received during the growing season) and timing
of rainfall is as important as total amount. Over the 18-yr
study period, the annual average precipitation was 324
mm, of which 108 mm was in the form of snow. A sub-
stantial proportion of the latter can disappear as sublim-
tion, snow blowoff and, after melting, as surface runoff.
No runoff from rainfall was observed during the growing
season. The 18-yr mean PET (calculation method de-
scribed in Section 2.2 below) was 661 mm.
The rotation experiment consisted of 12 cropping sys-
tems, of which we discuss five of the special plots. Spe-
cial plots (0.04 ha each) were sampled for soil water and
above-ground plant dry matter eight times between
spring and fall of each year between 1967 and 1984 [28,
29]. The experiment has been described in numerous
publications [23,24,30,31], thus we only present infor-
mation required to assess the factors examined.
The treatments examined were summer fallow-wheat
F-(W), summer fallow-wheat-wheat-F-W-(W), and con-
tinuous wheat (Cont W) each receiving N and P fertilizer,
and (F)-W-W and (Cont W) each receiving only P fertil-
izer. The rotation phase shown in parentheses was the
special plot treatment. Fertilizer N and P were applied in
accordance with the soil NO3-N (0 - 0.6 m depth) and
soil P (0 - 0.15 m depth) levels in individual plots,
measured the previous fall (mid-October) [30]. Fertilizer
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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222
N, as ammonium nitrate, was applied by broadcasting it in
spring prior to seedbed preparation. We used N rates
recommended by the soil testing laboratory at the Uni-
versity of Saskatchewan [32]. Wheat grown on summer
fallow received about 9 kg·N·ha–1·yr–1 and wheat grown
on stubble received an average of 30 kg·N·ha–1·yr–1 during
the 18-yr period. Phosphorus fertilizer (monoammonium
phosphate) was applied with the seed, with the desig-
nated treatments receiving 9 to 10 kg·N·ha–1·yr–1 in ac-
cordance with the general recommendations for the area
and crop [33]. Nitrogen in the P source was accounted
for in the N rates. All phases of each rotation were pre-
sent each year. There were three replicates.
Full-sized farm equipment was used for all field op-
erations. Tillage on summer fallow was performed two
to five times with a heavy-duty cultivator and/or rod
weeder. Late fall application of 2,4-D ester to control
broadleaf weeds was customary and other herbicides
were applied to cropped areas as required [31]. No fall
tillage was performed on the plots. The field manage-
ment operations (i.e., seedbed preparation, in-crop her-
bicide application, seeding, harvesting, and tillage of
summer fallow areas) were generally similar to those
discussed previously [34].
Seeding dates ranged from May 3 to June 5 (average
May 17) and harvest dates ranged from August 16 to
September 23 (average September 1).
2.1. Plant and Soil Sampling
At the three-leaf, five-leaf, shot blade (also known as
flag leaf complete) and soft dough growth stages, which
on the Feekes scale [35] correspond approximately to
stages 1, 2, 10 and 10.5.3, respectively, and at harvest,
plant samples were taken from two plant rows, each 3 m
long and located 1 m from the edge of the plot (sampled
area = 1.115 m2). Plant samples were dried at 70˚C and
the mass of the above-ground parts determined. The soil
was sampled at the aforementioned growth stages, as
well as prior to spring seeding in early May, at plant
emergence, at harvest, and in the fall, just prior to freeze-
up. The fallow plots of rotation (F)-W-W (+P) were
sampled at the same time as the cropped plots and
therefore its sampling times will also be referred to as
spring, emergence, three-leaf, etc. Over the 18-yr period
most sampling stages occurred within a 2- to 4-wk range.
Soil samples were taken (three cores per plot were
bulked) from the 0 - 0.15, 0.15 - 0.3, 0.3 - 0.6, 0.6 - 0.9
and 0.9 - 1.2 m depths. These samples were analyzed for
gravimetric soil water content, which was converted to
volumetric units using measured bulk densities of 1.20,
1.22, 1.26, 1.49 and 1.67 Mg·m–3 for the five depths,
respectively [28]. The lower limits of available water, i.e.
the permanent wilting point, as determined from field
measurements [36] were 27, 28, 28, and 31 mm for the 0
- 0.3, 0.3 - 0.6, 0.6 - 0.9 and 0.9 - 1.2 m depths respec-
tively, for a total of 114 mm for the 1.2-m depth. Water
contents at –0.03 MPa (i.e., field capacity) were 88, 87,
97 and 109 mm for the same depth intervals, for a total
of 381 mm for the 1.2-m profile [37].
2.2. Weather Data
Daily maximum and minimum air temperatures and
precipitation were measured at a meteorological site
located 1 km west of the experimental site. Potential
evapotranspiration was estimated from a regression
equation relating latent evaporation (i.e., evaporation
from Bellani plate atmometers) to meteorological infor-
mation [38]. Although equations using a number of
weather elements were developed, the most common one,
using daily maximum and minimum air temperature data,
was used:
LE = 0.928 Tmax + 0.933 Trange + 0.0486 Qo – 87.03
where, LE is latent evaporation from a Bellani plate sur-
face (cm3·day–1), Tmax is daily maximum temperature
(˚F), Trange is the difference between daily maximum
and daily minimum temperature (˚F), and Qo is the daily
amount of solar radiation at the top of the atmosphere
(cal·cm–2). The latter can be calculated for a given lati-
tude and day of the year. LE is multiplied by a factor of
0.096 to obtain PET in mm·day–1 [39]. The empirical
Baier-Robertson equation, which has been calibrated and
validated for Canadian conditions, was chosen over the
more physically based Penman-Monteith formulation,
because net radiation, windspeed and humidity data were
not continuously available during the 18-yr study period.
2.3. Data Anal ysis
Grain yields and above-ground plant biomass at the
various stages of growth were related by regression
analysis to water use (WU) and relative water use, WU/
PET. Water use was defined as: (spring soil water - soil
water at a later stage) + precipitation received during
that period.
3. RESULTS
3.1. Soil Water under Summer Fallow
3.1.1. Eighteen-yr Mean Soil Water Contents
Producers use summer fallow to conserve extra water
for the next crop. The main portion of the 20-mo fallow
eriod in which water is conserved in the semiarid prai- p
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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223223
Ta b le 1 . 18-yr (1967-1984) mean soil water (0 - 1.2 m depth), above-ground dry matter, and precipitation (PPT) received between
sampling times in five crop rotation phases at Swift Current, Saskatchewana.
Rotation Phase Sampled
(F)-W-W(+P) F-(W) (N+P) F-W-(W) (N+P) Cont W (N+P) Cont W (+P)
Average
calendar
day
Stage
sampled Soil water
(mm)
Soil water
(mm)
Dry matter
(kg·ha–1)
Soil water
(mm)
Dry matter
(kg·ha–1)
Soil water
(mm)
Dry matter
(kg·ha–1)
Soil water
(mm)
Dry matter
(kg·ha–1) Period Period PPT
(mm)
123 Spring
(Sp) 213 251 - 211 - 210 - 203 -
Sp to
Em 29.2
151 Emergence
(Em) 217 248 - 218 - 211 - 210 -
Em to
3L 17.5
162 Three-leaf
(3L) 222 252 90 217 87 214 87 211 78
3L to
5L 29.8
177 Five-leaf
(5L) 225 246 503 214 422 211 424 213 365
5L to
SB 28.1
188 Shot blade
(SB) 224 215 1792 192 1343 190 1428 188 1176
SB to
Do 52.1
224 Soft dough
(Do) 230 158 5130 157 3808 152 3788 158 3102
Do to
Ha 11.1
238 Harvest
(Ha) 233 154 4957 150 3706 150 3463 154 2877
Ha to
Fa 40.9
290 Fall (Fa) 238 161 - 160 - 160 - 162 -
Sp to
Fa 208.7
aSoil water and dry matter are for rotation phases shown in parentheses.
rie is the 5.5-mo period from May to mid-October [5].
Thus we observed an 18-yr average gain in soil water in
the 0 - 1.2 m depth of 25 mm (i.e., 0.15 mm·day–1) dur-
ing this period (Table 1). On average, the 0 - 0.3 m
depth starts in spring close to 70% of field capacity with
a little over 60 mm of water stored from the first eight
months of the fallow period (Figure 1). Between spring
and fall, the water content in this segment stayed fairly
constant as gains from precipitation were balanced by
evaporation and drainage losses. Water in the 0.3 - 0.6 m
depth at the spring sampling time was slightly over 50
mm and the amount gradually increased to as much as
that in the 0 - 0.3 m depth by the shot blade stage (Cal-
endar day 188), and thereafter remained constant at
slightly over 60 mm (like in the 0 - 0.3 m depth) until
fall. Water in the 0.6 - 0.9 m and 0.9 - 1.2 m depths was
about the same (45 mm) at the spring sampling. The
water contents in these two depths increased gradually
until the end of August, when it reached about 55 mm,
i.e., slightly above 50% of field capacity.
3.1.2. Soil W ater Con tents under Summer Fallow
during Selected Years
As might be expected, the amount of water stored and
the pattern of gain over time were quite variable, de-
pending primarily on the rainfall frequency, the amount
years (1970 and 1982) (Figure 2).
In 1968, 177 mm precipitation that was well distrib-
uted throughout the season was received between spring
and fall (Figure 2(a)). The PET during this period was
calculated to be 579 mm, and as a result the soil profile
only gained 25 mm of water, or 14.1% of the precipita-
tion. The early increases of about 28 mm of water in the
0.3 - 0.9 m depth between spring and emergence was
received, and also on the temperature and wind which
control evaporation in the southern prairies. We present
examples of trends in water storage under fallow [(F)-W-
W (+P)], in two dry years (1968 and 1973) and two wet
peculiar because there was little precipitation received in
this period (15 mm). We suspect that this anomaly might
be due to spatial variability because the coefficient of
variation of the sampled spring soil water content was
high, i.e., 39%. From emergence to fall, the soil water
contents of all depths remained fairly constant, except
between harvest and fall when the 0 - 0.6 m depth re-
flected the substantial precipitation (91 mm) received
during this period.
With only 87 mm precipitation and PET totalling 626
mm between spring and fall, 1973 represented a very dry
year (Figure 2(b)). The 0 - 0.3 and 0.3 - 0.6 m depths
gradually lost water throughout the spring to harvest
period, while the water content in the 0.6 - 0.9 m depth
remained fairly constant. On the other hand, the 0.9 - 1.2
m depth gained 12 mm water from spring to the five-leaf
stage, and then remained relatively constant. Thus there
was evidence of water moving from upper to lower
depths prior to the five-leaf stage. Overall, 21 mm of
water was lost from the soil profile under summer fallow
conditions due to evaporation exceeding the well dis-
tributed, but small occurrences of precipitation events in
this dry year.
During the very wet years of 1970 and 1982, when
summer fallow started in the spring with a modest
amount of water in the profile (220 mm and 170 mm,
respectively), large amounts of precipitation received in
ay and/or June, before evaporative demands were very M
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224
Figure 1. 18-yr mean trend in soil water content under summer fallow [(F)-W-W (+P)] as a function of time of sam-
pling, precipitation received during the sampling periods, and depth (successive sampling times are spring, emergence,
three-leaf, five-leaf, shot blade, soft dough, harvest and fall).
high, resulted in marked gains in soil water, i.e., 53 mm,
or 18.5% of the precipitation, in 1970 and 105 mm, or
31.6% of the precipitation in 1982 (Figures 2(c)-(d)).
About half (142 mm) of the total precipitation received
in 1970 fell in a one week period between the three- and
five- leaf stage, causing wetting of all depths to 1.2 m
and possible deeper. After the five-leaf stage small rain-
fall events were balanced by evaporation and thus, bar-
ring the anomalous water contents in the 0.9 - 1.2 m
depth at the soft dough stage and the one in the 0 - 0.3 m
depth at harvest, the soil water contents of all depths
remained constant till fall. In 1982, when the precipita-
tion was better distributed throughout the season than in
1970, soil water contents in the upper two depths
reached almost field capacity at the five-leaf stage and
stayed constant and high till harvest before increasing
slightly till fall. The steady gains in water in the 0.6 - 1.2
m depth were 84% of those in the 0 - 0.6 m depth.
Water draining beyond the 1.2 m depth during wet
years has also been demonstrated in several soil water
simulation studies [37,40,41]. Thus, the amount of water
conserved during the summer months under summer
fallow depends on the complex combination of amount
and time-distribution of precipitation received, the initial
soil water content in spring, and the evaporative de-
mands during the season.
3.2. Soil Water under a Crop
3.2.1. Eighteen-yr Mean Soil Water Contents for
0 - 1.2 m Dept h
Soil water conditions under cropped systems in the
semiarid prairies reflect the net balance between pre-
cipitation received and water lost via evaporation and
transpiration. Drainage through the root zone should be
rare except when very wet conditions occur in the early
part of the growing season, before the crop is well estab-
lished. The 18-yr mean amount of soil water in 0 - 1.2 m
depth under wheat being grown on fallow [F-(W) (N+P)]
was approximately 250 mm from spring to the five-leaf
stage; thereafter, soil water decreased rapidly to 158 mm
at the soft dough stage (i.e., at a rate of 1.87 mm·day–1)
(Table 1). Between harvest and fall there was an average
gain of about 7 mm of water in response to an average
precipitation of 41 mm received in this 52-day period.
The 18-yr mean soil water content in the 0 - 1.2 m
depth at spring sampling under well-fertilized stubble
rop wheat systems [e.g. F-W-(W) (N+P) and Cont W c
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225225
Figure 2. Examples of soil water contents under summer fallow [(F)-W-W (+P)] as a function of time of sampling, daily
precipitation, and depth for four selected years (values in brackets are precipitation totals between spring and fall).
(N+P)] was 210 mm (Table 1). Generally, these drier
systems gained a few mm of water by the three-leaf
stage, as gains from precipitation exceeded losses due to
low evapotranspiration rates related to minimal dry mat-
ter production and generally cool spring conditions. Here
too, as was the case for wheat grown on fallow [F-(W)
(N+P)], soil water in the profile decreased rapidly be-
tween the five-leaf and soft dough stage to about 155
mm in 1.2 m depth (at about 1.23 mm·day–1). Between
harvest and fall these well fertilized, stubble cropped
systems then gained on average 10 mm of water from
the 41 mm of precipitation received in this period.
As discussed by [6], Cont W (+P), because it had less
standing stubble than Cont W (N+P), trapped less snow
over winter; thus in spring, on average, it started with
about 7 mm less water in the profile (Table 1). Like
well-fertilized systems of wheat grown on stubble, Cont
W (+P) gained a small amount of water (10 mm) be-
tween the spring sampling and the five-leaf stage, then,
like the other cropped systems, it lost water rapidly at a
rate of 1.17 mm·day–1 until the soft dough stage, before
regaining about 8 mm between harvest and fall. Note
that the rates of decrease in soil water during the period
of rapid growth (i.e. the five-leaf to soft dough stage)
were proportional to the rate of above-ground dry matter
production (Table 1). This suggests that transpiration
was mainly responsible for the water loss in that period.
3.2.2. Eighteen-yr Mean Soil Water Contents at
Individ ual Depths
The 18-yr mean soil water content in the 0 - 0.3 m and
0.3 - 0.6 m depths at spring sampling under wheat being
grown on summer fallow [F-(W) (N+P)] was about 64
mm (Figure 3(a)). Soil water remained almost constant
till the three-leaf stage (five-leaf stage for the 0.3 - 0.6 m
depth), then decreased sharply to about 35 mm at the
soft dough stage as evapotranspiration markedly ex-
ceeded precipitation. The soil water contents then re-
mained constant for a short time until harvest. Between
harvest and fall (with no transpiration) the water content
of the 0 - 0.3 m depth was recharged with precipitation
to reach about 46 mm of water by the fall sampling. The
water content of the second depth remained constant till
fall, as excess precipitation between harvest and fall was
insufficient to wet the soil beyond the 0.3 m depth. Both
the 0.6 - 0.9 m and 0.9 - 1.2 m depths had about 59 mm
of soil water at the spring sampling, and water levels in
these two depths remained almost constant till the five-
leaf stage before decreasing slightly in both depths till
the shot blade stage. Thereafter, soil water in both of
these segments decreased sharply, though faster in the
.6 - 0.9 m depth, till harvest, and then remained con- 0
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226
Figure 3. 18-yr mean trend in soil water content under spring wheat as a function of time of sampling, precipitation received
during the sampling periods, and depth (successive sampling times are spring, emergence, three-leaf, five-leaf, shot blade, soft
dough, harvest and fall).
stant till fall when the 0.6 - 0.9 m depth had about 38
mm and the 0.9 - 1.2 m depth had about 46 mm of water.
Thus, in the F-(W) (N+P) system most of the water
was used between the five-leaf and soft dough stage, and
mainly from the top 0.6 m of soil. This was related to the
period of greatest growth (Ta b l e 2 ) and evapotranspira-
tion. Water was used more slowly from the 0.6 - 0.9 m
depth and even more slowly from the 0.9 - 1.2 m depth.
After harvest there was generally only sufficient extra
water to recharge the 0 - 0.3 m depth by the fall.
Soil water distribution with depth and changes from
spring to fall were similar for the stubble crop systems
F-W-(W) (N+P) and Cont W (N+P) (Figures 3(b)-(c));
therefore, we will only discuss the results for Cont W
(N+P). Soil water content and response in the 0 - 0.3 m
depth between spring and fall in this system were almost
identical to that of a summer fallow crop system F-(W)
(N+P) (Figure 3(a)). The stubble crop system, with
much less time for soil water to be recharged (8 mo vs
20 mo), had only about 51 mm of water in the 0.3 - 0.6
m depth in spring. There was sufficient precipitation and
maybe some drainage from the 0 - 0.3 m depth to
slightly increase the soil water content in the 0 - 0.6 m
depth to about 55 mm by the five-leaf stage. From the
five-leaf to the soft dough stage, soil water in both the 0
- 0.3 and 0.3 - 0.6 m depths decreased sharply and line-
arly at the same rate to about 35 mm, which is similar to
that for the F-(W) (N+P) system. Thereafter, as for F-(W)
(N+P), soil water in the 0 - 0.3 m depth increased, and
that of the 0.3 - 0.6 m depth remained constant, until fall.
Soil water in the 0.6 - 0.9 m and 0.9 - 1.2 m depths, like
in the 0.3 - 0.6 m depth, started the spring with much
less water than in F-(W) (N+P). Although this pattern of
water loss from these two lower depths mimicked those
for the respective depths in F-(W) (N+P), the lower rate
of water use by the lower-yielding stubble crop com-
pared to the fallow crop (Table 2), resulted in less water
being taken-up from these two depths under the stubble
crops. Consequently, the soil water contents in these
lower depths were generally similar in Cont W (N+P), F-
W-(W) (N+P) and F-(W) (N+P) by fall.
Soil water content in the 0 - 0.3 m depth under Cont
W receiving only P [(Cont W (+P)] (Figure 3(d)) was
similar in amounts and distribution with depth as Cont
W (N+P) from spring to fall. However, soil water in the
0.3 - 0.6 m depth under Cont W (+P) exceeded that in
the 0 - 0.3 m depth from spring to the five-leaf stage
constant at about 66 mm). This may be related to the (
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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227227
Tab le 2. Effect of cropping frequency and N fertilizer on above-ground dry matter accumulation at Swift Current, Saskatchewan
(1967-1984)a.
Dry matter (kg·ha–1)
Year Stage
F-(W) (N+P) F-W-(W) (N+P)Cont W (N+P)Cont W (+P)
PPTb (mm)
(Spring to harvest)
PETc (mm)
(Spring to harvest)
1967 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
161
606
1474
2984
3401
128
522
1329
2960
3834
111
566
1376
2489
3345
67
345
1032
2210
2687
54 450
1968 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
84
432
1072
2237
3044
101
432
917
1198
1243
121
502
1169
1306
1261
91
358
764
1346
1315
87 466
1969 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
101
355
911
2013
4379
104
348
897
2083
3992
108
318
917
2076
4302
101
237
794
2023
3694
135 464
1970 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
37
348
2060
5107
3410
44
311
1256
3633
3107
54
429
1742
4202
3310
57
452
1882
3473
2486
244 460
1971 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
50
419
3536
7059
5491
57
375
2267
3667
3405
67
476
2930
3490
3709
71
372
1762
3051
2976
124 522
1972 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
50
177
897
4082
3360
64
281
1075
4116
3730
60
214
884
3606
2337
60
224
961
3832
2379
155 536
1973 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
50
991
1799
3596
2888
47
532
1156
3064
2418
37
535
1178
3473
2588
34
465
991
2505
2251
64 503
1974 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
104
917
2019
4488
5435
104
717
1956
3231
3896
111
791
1979
3483
3778
114
724
1711
3366
3643
258 464
1975 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
111
1215
3128
5486
3489
101
853
2144
4357
3375
101
747
2164
4756
3870
84
687
1861
3985
3468
210 457
1976 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
134
515
3610
9417
8053
141
603
3074
6343
5563
148
556
3295
6772
5100
101
489
2368
5486
5030
223 479
1977 Three-leaf
Five-leaf
Shot blade
Soft dough
134
429
2063
8774
74
180
964
7090
84
221
1142
6480
71
207
1175
5419
227 551
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Harvest
7719 5796 5337 4725
1978 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
57
261
680
3211
5602
77
626
1122
3014
3021
64
483
1089
2388
2892
67
355
754
1953
1902
135 510
1979 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
-
214
1018
4601
4565
-
161
995
2746
3521
-
177
1105
3543
3491
-
207
724
2270
2535
131 487
1980 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
-
321
840
5579
5184
-
174
442
3643
2827
-
108
399
2689
2418
-
148
442
1725
2027
189 550
1981 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
-
-
-
-
6284
-
-
-
-
4282
-
-
-
-
3670
-
-
-
-
2573
211 484
1982 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
60
416
1185
9353
8742
64
368
1105
6339
6166
77
355
1068
6627
4967
57
315
646
5392
4237
285 466
1983 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
-
-
-
-
-
87
375
890
5914
5787
84
375
512
5639
5220
-
-
-
-
-
150 441
1984 Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
124
436
2384
4082
3220
114
311
1239
1333
757
94
355
1333
1373
757
121
261
958
1604
990
113 494
Mean Three-leaf
Five-leaf
Shot blade
Soft dough
Harvest
90
503
1792
5130
4957
87
422
1343
3808
3706
87
424
1428
3788
3463
78
365
1176
3102
2877
167 488
aSome data, especially in 1981 and 1983, were missing; bPPT = precipitation; cPET = potential evapotranspiration.
reduced water uptake by a crop whose early growth is
partly restricted by inadequate nitrogen fertility [6]. The
pattern of water response in the 0.3 - 0.6 m depth under
Cont W (+P) was similar to that of the other cropped
systems. Soil water patterns and contents in the 0.6 - 0.9
m and 0.9 - 1.2 m depths under Cont W (+P) were gen-
erally similar to those under Cont W (N+P). There was
about 45 mm of water in each of these two depths be-
tween spring and the shot blade growth stage. There-
after, water was slowly and gradually lost from these
two depths till harvest, but from the 0.6 - 0.9 m depth
moreso than from the 0.9 - 1.2 m depth (Figure 3(d)).
No water gains occurred in these lower depths between
harvest and fall.
3.2.3. Soil Water Contents during Selected Years
In four selected years of varying precipitation, soil
water contents in the profile varied from the 18-yr mean
pattern (Figure 4). In the period prior to the five-leaf
stage and after harvest, the 0 - 1.2 m depth soil water
content was mainly related to precipitation. For example,
in 1970 the very wet month of June caused the soil water
content to increase from 261 mm at the spring sampling
to 308 mm at the five-leaf stage (Figure 4(a)). However,
in 1976, when spring precipitation was only moderate
see Figure 4(b)); the soil water content was fairly con- (
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229229
Figure 4. Examples of trends in soil water content in the 0 - 1.2 m depth under spring wheat grown on fallow [F-(W) (N+P)]
for four typical years (values in brackets are the precipitation totals between spring and fall).
stant to the five-leaf stage (Figure 4(b)). Transpiration
during this early part of the growing season was gener-
ally low. Similarly, precipitation dictated the pattern of
soil water trends after the soft dough stage when the crop
was no longer withdrawing soil water. In dry years such
as 1971 and 1973 when little precipitation fell before the
five-leaf stage, the soil water content decreased rapidly
from early spring onwards (Figures 4(c)-(d)). In all sys-
tems the rapid growth between the five-leaf and soft
dough stages (Table 2) was accompanied by a rapid de-
crease of soil water, irrespective of the amount of pre-
cipitation received, as evapotranspiration far exceeded
precipitation.
Soil water distribution in the profile from spring to
fall under a crop, was similar under F-(W) (N+P) as un-
der Cont W (N+P), therefore we show only a couple of
examples for Cont W (N+P) for two dry years (1968 and
1973), and for two wet ones (1970 and 1982) (Figure 5).
In 1968, 177 mm of precipitation fell between spring and
fall, of which almost 90 mm was received outside the
growing season, between harvest and fall. (Figure 5(a)).
Most of the changes in soil water content occurred in the
0 - 0.3 m depth; after an initial slow decrease from
spring to the three-leaf stage, the water content rapidly
decreased to near the wilting point by the shot blade
stage, remained constant till the soft dough stage and
then increased till fall to about 60 mm in response to the
121 mm precipitation received in this late period. The
low spring soil water contents in the 0 - 0.3 m and 0.3 -
0.6 m depths reflect the dry conditions of the previous
year and the small amount of overwinter precipitation
(74 mm between fall and spring) that did not wet the soil
beyond the 0.3 m depth. All depths below 0.3 m gradu-
ally lost small amounts of water till the shot blade stage,
as water use by the crop slightly exceeded the rainfall
replenishment. The small amount of water uptake by the
crop (133 mm) was reflected in the low total dry matter
production [maximum at the soft dough stage, 1306 kg·ha–1
(Table 2)]. The increase in soil water content at the 0.6 -
0.9 m depth between the three- and five- leaf stage may
be a sampling error because there was no precipitation
during this period.
The year 1973 was even drier than 1968, with only 64
mm precipitation well-distributed between spring and
harvest (Figure 5(b)). The soil water content in the 0 -
0.3 m depth decreased almost linearly from spring to
harvest, and then increased slightly from harvest to fall
n response to the late small precipitation events. The i
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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230
Figure 5. Soil water distribution with depth (spring to fall) under stubble wheat [Cont W (N+P)] for two dry (1968 and 1973)
and two wet (1970 and 1982) years (values in brackets are the precipitation totals between spring and fall).
water content of the 0.3 - 0.6 m depth decreased slowly
from spring to the three-leaf stage, then rapidly to the
soft dough stage before levelling off at maturity. This
pattern reflects plant growth and crop water uptake. Be-
cause of low rainfall, the soil water content of the 0.6 -
0.9 m depth remained constant till the five-leaf stage,
reflecting the time it takes for roots to reach this depth.
Thereafter, water loss was linear to the soft dough stage
and more slowly till the fall sampling date. Generally,
between the five-leaf stage and harvest, water losses
from the 0.3 - 0.6 m depth and from the 0.6 - 0.9 m
depth were parallel to each other. In the 0.9 - 1.2 m
depth the soil water content remained relatively constant
from emergence to the shot blade stage, then decreased
slowly, but linearly to harvest and even more slowly till
fall. The marked loss of soil water from all four depths
from spring to harvest, a total of 194 mm, was reflected
in a dry matter production of 3473 kg·ha–1 at the soft
dough stage (Table 2), almost three times higher than in
1968.
The two wet years shown as examples differed in that
50% (142 mm) of the period precipitation received in
1970 occurred during a single week in June (Figure 5(c))
while the 332 mm of precipitation received in 1982 was
well-distributed throughout the period (Figure 5(d)).
Thus, plant dry matter production was much greater in
1982 than in 1970 [6627 kg·ha–1 vs 4202 kg·ha–1 at the
soft dough stage (Ta bl e 2 )] and presumably evapotran-
spiration would also have been much greater in 1982.
The balance between evapotranspiration and precipita-
tion favoured drainage in 1970 as was evidenced by a
rare occurrence under crop when all soil segments to 1.2
m depth (and probably beyond) showed an increase in
water content between the three- and five- leaf stage
(Figure 5(c)). All soil depths then lost water rapidly
between the five-leaf and soft dough stage in 1970, then
they remained constant, except for the 0 - 0.3 m depth
which gained water between harvest and fall, reflecting
the 40 mm of rainfall received in this period.
In 1982, the low spring soil water contents in the 0.3 -
1.2 m depth reflect the lower than normal fall soil water
contents in 1981 and the small amount of overwinter
precipitation (95 mm between fall and spring) that did
not wet the soil beyond the 0.3 m depth. Large amounts
of precipitation received prior to the five-leaf stage (177
mm) markedly increased the soil water content in the 0 -
0.6 m depth and to a lesser extent that in the 0.6 - 0.9 m
depth. However the 80 mm of precipitation received
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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231231
between the shot blade and soft dough stage was more
than counter-balanced by high evapotranspiration, and
consequently the 0 - 0.9 m depth lost significant amounts
of water (82 mm). Between the harvest and fall sampling,
when there is no transpiration, the 50 mm precipitation
received increased the water content in the 0 - 0.3 m
depth by 35 mm, with no wetting below this depth. The
soil water content in the 0.9 - 1.2 m depth remained rela-
tively constant throughout the growing season, suggest-
ing that sufficient water was available for good crop
growth in the upper three depths.
3.3. Dry Matter Production and Water Use
(WU)
We calculated WU and total above-ground dry matter
production between spring and each sampling time for
Cont W (N+P) and Cont W (+P), in order to assess the
influence of N fertilizer on this parameter (Ta b l e 3 and
Figure 6). A regression of dry matter accumulated to
each growth stage vs WU was linear for both treatments
(Figure 6). The y-intercepts were not significantly dif-
ferent (P < 0.05), but the regression slopes were signifi-
Table 3. Effect of N fertilizer on relationship between total dry matter (TDM) accumulation versus water use (WU), potential
evapotranspiration (PET) and relative water use (WU/PET) at Swift Current, Saskatchewan. The values are 18-yr means ρ standard
deviation.
Change in soil water
(0 - 1.2 m depth)
Precipitation
(Spring to period)
WUa
(Spring to period)
PET
(Spring to period)
Period Treatment (Spring to period) WU/PET TDM
(mm) (kg·ha–1)
Spring to three-leaf Cont W (N+P)
Cont W (+P)
–1 ρ22
–5 ρ21
48 ρ35
48 ρ35
47 ρ26
43 ρ28
143 ρ24
143 ρ24
0.329 ρ0.157
0.301 ρ0.178
87.0 ρ29.2
78.3 ρ24.6
Spring to five-leaf Cont W (N+P)
Cont W (+P)
–2 ρ34
–11 ρ29
75 ρ48
75 ρ48
73 ρ33
64 ρ34
199 ρ24
199 ρ24
0.367 ρ0.176
0.322 ρ0.179
424 ρ189
365 ρ166
Spring to shot blade
Cont W (N+P)
Cont W (+P)
20 ρ37
14 ρ34
103 ρ52
103 ρ52
123 ρ39
117 ρ37
264 ρ23
264 ρ23
0.467 ρ0.141
0.443 ρ0.141
1428 ρ780
1176 ρ559
Spring to soft dough Cont W (N+ P)
Cont W (+P)
58 ρ30
44 ρ28
155 ρ68
155 ρ68
213 ρ57
199 ρ51
429 ρ34
429 ρ34
0.497 ρ0.132
0.464 ρ0.119
3788 ρ1748
3102 ρ1399
Spring to harvest Cont W (N+P)
Cont W (+P)
60 ρ31
48 ρ28
166 ρ67
166 ρ67
226 ρ55
215 ρ52
488 ρ34
488 ρ34
0.463 ρ0.126
0.440 ρ0.115
3463 ρ1289
2877 ρ1124
aWU = (Increase in soil water between spring and a later period) + precipitation received in the period.
Figure 6. Effect of N fertilizer on the relationship between dry matter accumulation and water use.
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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232
cantly different at P < 0.10. The equations indicated
early season evaporation (WU intercept) was 39 mm for
Cont W (N+P) and 36 mm for Cont W (+P). The later
season evapotranspiration (WU) efficiency (slope of the
regression line) was 19.2 kg·ha–1·mm–1 for Cont W (N+
P) compared to 16.7 kg·ha–1 ·mm–1 for Cont W (+P).
These slopes are much lower than the 33.0 kg·ha–1·mm–1
slope reported by [42] for winter triticale (xTriticosecale
Wittmack) grown in Colorado, but similar to values 21.3
and 18.9 kg·ha–1·mm–1 reported in [43] from a study
done by [44] which showed a positive effect of P fertil-
izer on water use efficiency of wheat. They observed the
greatest difference in evapotranpiration at any growth
stage to be 12 mm for P treatments, while we observed a
mean maximum difference in WU of 14 mm during the
spring to soft dough stage (Table 3). The early-season
evaporation in the [44] study was 32 mm, while in our
study it averaged 38 mm. We also determined the rela-
tionship between total dry matter produced and WU
relative to potential evapotranspiration (WU/PET) (Ta-
ble 3), but found no significant effect of N fertilizer in
this case.
3.4. Grain Yield, Water Use and Relative
Water Use
The annual grain yields, water use and relative water use
(WU/PET) for each treatment (Table 4) were used to
construct regression equations (Figure 7). The relation-
ships between wheat yield and water use were signifi-
cant (P < 0.05) for all treatments (Figure 7(a)). The wa-
ter use efficiency (i.e., the slope of the regression line)
was slightly greater for well-fertilized wheat grown on
fallow [F-(W) (N+P)] than for well-fertilized wheat
grown on stubble [F-W-(W) (N+P) and Cont W (N+P)],
and the latter slightly greater than for stubble wheat
without N fertilizer [Cont W (+P)]. However, the regres-
sions were not significantly different (P < 0.05), and
therefore we pooled the data and derived a single regres-
sion: Y = 8.91X – 648 (Figure 7(a)). This equation sug-
gests a yield increase of nearly 9 kg·ha–1·mm–1 water
used, and 73 mm of evapotranspiration required before
the first kg·ha–1 of grain is produced in this semiarid
region. These values are generally similar to those re-
ported previously by [24,45,46] for systems in southern
Saskatchewan and Alberta, but lower than the slope
(12.49 kg·ha–1·mm–1) and intercept (132 mm) reported
by [47] for winter wheat in Colorado. A regression of
yield against water use normalized per unit of PET did
not improve the relationship compared to that with water
use alone (Figure 7(b)).
4. DISCUSSION
This rotation study has been ongoing for 40 yr, during
which the first 18 yr discussed in this paper were much
drier than the subsequent 22 years [6]. Thus, it is not
surprising to find that the 18-yr mean amount of water
conserved under summer fallow during the 5.5 mo.
summer period (25 mm) was 16% less than the 31 mm
40-yr average observed for this period by [6]. Annual
analysis of soil water conserved under summer fallow
throughout the summer months showed that the pattern
of soil water accumulation throughout the soil profile
Ta bl e 4 . Growing season precipitation (GSP), potential evapotranspiration (PET), water use (WU)a, relative water use (WU/PET)
and grain yields - effect of cropping frequency and N fertilizer at Swift Current, Saskatchewan (1967-1984)b.
Cont W (N+P) Cont W (+P) F-W-(W) (N+P) F-(W) (N+P)
Year GSP
(mm)
PET
(mm) Yield
(kg·ha–1)
WU
(mm) WU/PET Yield
(kg·ha–1)
WU
(mm) WU/PET Yield
(kg·ha–1)
WU
(mm)WU/PET Yield
(kg·ha–1)
WU
(mm) WU/PET
1967 54 450 1017 147 0.33 820 172 0.38 1139 158 0.35 987 171 0.38
1968 87 466 468 134 0.29 554 124 0.27 429 123 0.26 1264 179 0.38
1969 135 464 1070 177 0.38 1145 166 0.36 1091 181 0.39 1005 216 0.47
1970 244 460 1100 302 0.66 974 278 0.60 1160 296 0.64 1306 361 0.78
1971 124 522 1279 202 0.39 1109 172 0.33 1148 178 0.34 1842 251 0.48
1972 55 536 1038 207 0.39 983 207 0.39 1381 229 0.43 1342 221 0.41
1973 64 503 918 194 0.39 811 162 0.32 802 180 0.36 978 192 0.32
1974 258 464 1413 301 0.65 422 264 0.57 1419 297 0.64 1920 330 0.71
1975 210 457 1750 251 0.55 1636 263 0.58 1607 266 0.58 1539 280 0.61
1976 223 479 1652 273 0.57 1896 269 0.56 2004 300 0.62 2668 322 0.67
1977 227 551 1995 255 0.46 2060 263 0.48 2126 262 0.48 2752 326 0.59
1978 135 510 1017 212 0.42 754 200 0.39 1163 241 0.47 2060 253 0.50
1979 131 487 1529 212 0.44 1285 182 0.37 1618 233 0.48 1923 248 0.51
1980 189 550 960 212 0.38 9412 211 0.38 1279 202 0.37 2013 274 0.50
1981 211 484 1491 241 0.50 1160 253 0.52 1107 250 0.52 2140 297 0.61
1982 285 466 2087 321 0.69 1618 298 0.64 2275 317 0.68 2707 337 0.72
1983 150 441 1804 268 0.61 - - - 1929 241 0.55 - - -
1984 113 494 265 158 0.32 411 171 0.35 2412 147 0.30 1216 227 0.46
Mean
SDc
166
68
488
34
1270
492
226
54
0.47
0.13
1151
456
215
52
0.44
0.12
1328
543
228
58
0.47
0.13
1745
603
264
59
0.54
0.13
aWU = [spring soil water - harvest soil water (0 - 1.2 m depth)] + GSP; bData missing for CONT W (+P) and F-(W) (N+P) in 1983; cρ = standard deviation.
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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233233
Figure 7. Relationship between grain yield and (a) water use and (b) relative water use for wheat grown on fallow or stubble
receiving N and P or P only.
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
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234
was related to the initial water content of the soil and the
balance between the amount of precipitation received, its
distribution over time, and the strength of the evapora-
tive demands. The patterns of soil water accumulation
and drying occur first in the uppermost depth and gradu-
ally moved later to lower depths, as is assumed in soil
water simulation models [41,48,49].
Spring soil water contents under wheat grown on fal-
low were 40 mm higher than under stubble crops, and
while water remained constant till the five-leaf stage for
the former, the stubble crop, with lower soil water re-
serves in spring, gained a small amount of water till
about the three-leaf stage due to low transpiration rates
(caused by minimal crop growth) and low evaporation
rates (as a result of low temperatures).
Soil water changes under cropped systems mainly
showed the influence of precipitation during the periods
prior to and after the expansive growth of the crop had
occurred (five-leaf to soft dough stages). During the lat-
ter period soil water was rapidly lost in all cropped sys-
tems despite precipitation. The rate of water loss in this
period was greater for F-(W) (N + P) (1.87 mm·day–1)
than for Cont W (N + P) (1.23 mm·day–1) which was
greater than for Cont W (+P) (1.17 mm·day–1).
Under a crop, soil water is used progressively from
the uppermost depths, but rarely from the 0.09 - 1.2 m
depth, which suggests that deeper rooting crops like
winter wheat and/or safflower may be needed in the ro-
tation to extract more plant available water. Water re-
charge between harvest and fall primarily occurs in the 0
- 0.3 m depth. On one rare occurrence when 142 mm of
precipitation was received in early June, 1970, there was
evidence that drainage beyond 1.2 m may have occurred
under a cropped situation. This supports our findings
that there has been little NO3-N leaching from Cont W
after 37 yr in this study [50].
Regression analysis showed that withholding N from
Cont W was reflected in a reduced rate of above-ground
plant biomass production. This supports similar findings
by [44] regarding the influence of P on wheat production.
Regression analysis also showed that grain yields were
directly related to water use, with rates not significantly
influenced by cropping frequency nor fertilizer applica-
tions, although there was a tendency for a greater water
use efficiency for wheat grown on fallow than on stubble,
and for well-fertilized Cont W than for Cont W receiving
only P fertilizer.
In addition to the soil and plant parameters described
in this paper, measurements and analyses are available
for soil NO3-N [50,51] and bicarbonate extractable P [52,
53] at the same depths and with the same frequency as
the soil water content measurements. Analysis of total
organic N and C in the upper two soil depths were made
at irregular time intervals [54]. N and P concentrations in
the above-ground biomass (grain and straw) were meas-
ured at different phenological growth stages, for both
combine- and hand-harvested data [31,55]. The meas-
ured daily meteorological parameters include precipita-
tion, maximum and minimum temperatures, global ra-
diation and class A pan evaporation. Windspeed and
relative humidity data may be obtained from a nearby
weather station, located approximately 5 km NE of the
experimental plots. Soil and crop management informa-
tion on seedbed preparation, seeding, fertilizer and her-
bicide application, tillage operations and harvesting are
also available [28,56].
While several investigators [40,41,57-60] have used
these long term rotation data for testing and validating
their models, there is a wealth of information left to be
explored. For example, the measured P data have not
been used in any modelling exercise. We know of no
similar data sets where such detailed measurements have
been made for such a lengthy period. Soil and crop mod-
ellers are therefore invited to have a look at these in-
valuable data sets, and start using them.
5. SUMMARY
The effects of cropping frequency and N fertilization
on trends in soil water content and water use were
quantified using a long-term (18-yr) field experiment in
which multiple samplings were made each year. The
main findings of this study were:
1) In most years precipitation increased stored soil
water during non-cropping periods, (i.e. overwinter and
during summer fallow), wetting surface soil layers first
and then the lower layers. However, in very dry years
summer fallow treatments actually lost soil water.
2) A growing spring wheat crop used stored soil water
first from the surface layers and then gradually over time
from lower depths. Rarely was water extracted from
below 90 cm.
3) Soil water distribution with depth and over time
was different in dry years compared to wet ones.
4) Nitrogen fertilization improved (i.e., increased) the
slope of the water use/dry matter function.
5) The water use/grain production function was similar
to those previously reported for spring wheat in Saska-
tchewan and Alberta; it did not vary with cropping
intensity, nor with N fertilization.
6) The 18 years of detailed measurements of soil and
plant parameters under various cropping systems provide
researchers with a unique and invaluable source of
information for developing and testing soil-crop-mana-
gement simulation models. A copy of the data, including
daily weather data, can be obtained from Dr. R. P.
Zentner, Semiarid Prairie Agricultural Research Centre,
R. de Jong et al. / Agricultural Science 2 (2011) 220-237
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
235235
Agriculture and Agri-Food Canada, Swift Current, SK,
S9H 3X2, Canada (zentnerr@agr.gc.ca).
6. ACKNOWLEDGEMENTS
The authors acknowledge the technical assistance of staff at the
Semiarid Prairie Agricultural Research Centre in Swift Current for
maintaining the long-term crop rotation experiment and wish to thank
Valerie Kirkwood for stenographic assistance.
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