SEASONAL PRECIPITATION, EVAPORATION, SOIL MOISTURE,
AND YIELD OF FERTILIZED RANGE VEGETATION
A. JoHNSTON, S. SMOLIAK, A. D. SMITH AND L. E. Lurw1cK
Research Station, Canada' Department of Agriculture, Lethbridge, Alberta
Received September 19, 1968
ABSTRACT
Nitrogen and phosphorus fertilizers were applied to range vegetation at five
locations at rates ranging from 475 to 705 kg/ha N with or without from
380 to 545 kg/ha P. The addition of fertilizers increased average water-use
efficiency at all locations. Average magnitude of the increase in relation to
unfertilized controls was: control, 33.3 kg/ha dry matter produced per cm of
water; P, 37.0 kg/ha/cm; N, 52.3 kg/ha/cm; and, N+P, 73.4 kg/ha/cm. Fall
soil moisture had the greatest influence on yield of control and P-treated
range vegetation, whereas June precipitation had the greatest influence on yield
of N- and N+P-treated range vegetation.
INTRODUCTION
The rangelands of western Canada are located mostly in the semiarid portions
of the region. Forage yields tend to be low and undependable because of the
limited and uncertain rainfall.
Thus, it would be desirable in range management to determine whether
there are periods of favorable moisture when the soil nutrient supply limits
plant growth. In such periods, should they occur, fertilizers might increase
growth without increasing the water requirement or the rate of water use. The
latter is less critical on rangeland, where vegetative growth is harvested, than on
cropland, where seed must be produced (12).
Fertilizer application leads to a more efficient use of water by plants.
Investigators have reported increased efficiency in use of seasonal precipitation
through nitrogen fertilization of crested wheatgrass ( 10) and bromegrass­
crested wheatgrass (11). Briggs and Shantz (2) reviewed early studies and
concluded that " . . . the experiments . . . show a reduction in the water
requirement accompanying the use of fertilizers . . . . In poor soils the water
requirement may be reduced one-half or even two-thirds . . . . " Viets (12), in
a recent review, concluded that fertilization for the adequate nutrition of all
crops plays a major role in the efficient use and conservation of water resources.
The purpose of our study was to determine the relationship among yields
of range vegetation, unfertilized and fertilized with nitrogen and phosphorus,
and seasonal precipitation, evaporation, or soil moisture.
MATERIALS AND METHODS
Yield data were available from soil-plant relationship studies (3, 6) at five
locations across the rangelands of southern Alberta. Environments of study
locations differed. At Manyberries and Coalhurst the climate is semiarid,
annual precipitation ranges from 30 to 40 cm, soils belong to the Brown and
Dark Brown groups, and native vegetation is of the mixed prairie type. At
Magrath, Spring Point, and Stavely the climate is subhumid, annual precipitation
ranges from 45 to 50 cm, soils belong to the Dark Brown and Black groups,
and vegetation is of the fescue grassland type.
At each location, one application of ammonium nitrate (33.5-0-0), or of
triple superphosphate (0-45-0), or of both, was made with an increasing-rate
spreader (7) in October of 1961, 1962, and 1963. Fertilizer was applied in
Can. J. Plant Sci. Vol.
49, 123-128 (1969)
123
CANADIAN JOURNAL OF PLANT SCIENCE
124
[Vol. 49
replicated strips to a new section of the field at each location each year. Levels
of application that ranged from 475 to 705 kg/ha N, with or without from
380 to 545 kg/ha P, were selected for this study. The treatments were chosen
because results (3, 6) showed a yield response at these levels of P, N, or N+P
but little change in composition of vegetation. Yields reported in this study
were taken in the first crop year after fertilization.
Measurements of precipitation and evaporation were made throughout the
growing season. The procedure has been described (8). Five soil moisture
determinations were made on about April 30 and September 30 each year at
each location, at depths of 30, 60, and 120 cm. Samples, obtained with a soil
tube, were placed in airtight containers and weighed. Soil samples were dried
at 100°C for 24 hours and percentage soil moisture was calculated on the oven­
dried basis. These data were converted on the basis of bulk density deter­
minations, to cm of water in the soil profile, so that precipitation water and
soil water could be related directly.
Data were subjected to simple correlation and stepwise multiple regression
analyses. In all equations, Y is the estimated forage yield in kg/ha and X1-1a
are: (1) May precipitation; ( 2) June precipitation; (3) May-June precipitation;
(4) May-September precipitation; (5) May evaporation; (6) June evaporation;
(7) May-September evaporation; (8) spring soil moisture at 0-30 cm depth;
(9) spring soil moisture at 0-60 cm depth; (10) spring soil moisture at 0-120
cm depth; (11) fall soil moisture at 0-30 cm depth; (12) fall soil moisture at
0-60 cm depth; and (13) fall soil moisture at 0-120 cm depth.
RESULTS
Precipitation and spring and fall soil moisture contents were lower at Many­
berries and Coalhurst than at Magrath and Stavely, whereas evaporation was
higher (Table 1).
Correlation coefficients (Table 2) showed that fall soil moisture of the
previous year had the greatest influence on current yield of range vegetation.
Yields of control plots, P-treated plots and N-treated plots, and of all N+P­
treated plots except at the 0-30 cm soil moisture depth, were significantly
influenced by fall soil moisture at the 0-30 cm, 0-60 cm, and 0-120 cm depths.
May-June precipitation of the current year significantly affected yield, re­
gardless of fertilizer treatment. May-September evaporation was negatively
correlated with yield of control and P-treated plots and of N- and N+P­
treated plots.
·
Table 1.
Average seasonal precipitation, evaporation, and soil moisture at five locations
1962-64
Location
Precipitation
May-September
(cm)
Many berries
Coalhurst
Magrath
Spring Point
Stavely
15 .4
21.3
25.4
27.2
30.0
Evaporation
May-September
(cm)
137. 0
139.4
95.8
112 .1
98.9
Spring soil
moistnre
0-120 cm depth
(cm)
Fall soil
moisture
0-120 cm depth
( cm)
13.5
23.4
35.1
33.5
35 .4
10.1
17.5
27.9
25.8
26.5
March 1969]
Table 2.
JOHNSTON ET AL.-PRECIPITATION AND RANGE VEGETATION
125
Correlation coefficients of yield of unfertilized and fertilized range vegetation with
seasonal precipitation, evaporation, and soil moisture
Fertilizer treatment
Factor
Control
Precipitation (cm)
May
June
May-June
May-September
0.349
0.477
0.595*
0.420
Evaporation (cm)
May
June
May-September
-0.617*
-0 .343
-0.719**
p
0.311
0.493
0.593*
0. 429
-0.616*
-0.316
-0.720**
N
N+P
0 .265
0 .592*
0.664*
0 .514
0.045
0.684*
0.653*
0.541
-0.563
-0.326
-0.637*
-0.443
-0.386
-0.652*
Spring soil moisture (cm)
0-30 cm depth
0-60 cm depth
0-120 cm depth
0.647*
0.605*
0 .587*
0.624*
0.587*
0.580*
0.532
0.472
0.445
0.399
0.397
0.425
Fall soil moisture (cm)
0-30 cm depth
0-60 cm depth
0-120 cm depth
0.749**
0.822**
0.814**
0.736**
0.810**
0.788**
0.616*
0.687*
0.609*
0.532
0 .629*
0.614*
*Significant at P < 0.05.
**Significant at P < 0.01.
Water-use efficiency ranged from 15.3 kg/ha dry matter produced per cm
of water on unfertilized range at Manyberries to 125.5 kg/ha dry matter
produced per cm of water on range fertilized with N+P at Magrath (Table 3).
YVater-use efficiency at all locations increased significantly with the addition
of P (P < 0.05), further increased with the addition of N (P < 0.01), and was
greatest on plots treated with N+P (P < 0.01).
Data from each fertilizer treatment from each location were pooled and
were subjected to stepwise multiple regression analyses; regression equations
were summarized (Table 4). Significant goodness of fit was obtained follow­
ing the entry of three variables of control and P-treated plots, of two variables
of N-treated plots, but of only one variable of N+P-treated plots. Thus, three
factors-fall soil moisture at 0-60 cm depth, May-September evaporation, and
May-June precipitation-accounted for 94.7% of the variation in yield of
control plots and 90. 2% of the variation in yield of P-treated plots. Two
factors-June precipitation and May-September evaporation-accounted for
70.6% of the variation in yield of N-treated plots. One factor-June pre­
cipitation-accounted for 54.0% of the variation in yield of N+P-treated plots.
Fall soil moisture was most important and accounted for 67.6% and 65.6% of
the variation in yield of control and P-treated plots, respectively, while June
precipitation accounted for 62.9% of the variation in yield of N-treated plots.
DISCUSSION
Yield of range vegetation in the areas studied appeared to be dependent pri­
marily upon fall soil moisture and, secondly, upon precipitation during the
May-June growing season. May-September evaporation was correlated with
18.8
27.2
32.6
34.9
38.9
30.5
Manyberries
Coalhurst
Magrath
Spring Point
Stavely
Average
287
548
1810
1145
1670
1092
y
(kg/ha)
15.3
20 .2
55.5
32. 8
42.9
33.3
Y/ET
(k g/ha/cm)
330
615
1969
1329
1795
1208
y
(kg/ha)
17.6
22.6
60.4
38.1
46.1
37.0*
Y/ET
(kg/ha/cm)
p
y
606
1102
2763
1626
2239
1667
(kg/ha)
tBased on: Spring moisture content of soil in cm + seasonal precipitation in cm - fall moisture content of soil in cm
*Significantly higher than the control (P < 0.05).
**Significantly higher than the control (P < 0.01).
ETt
(cm)
Control
Fertilizer
=
evapotranspiration.
32.2
40.5
84.8
46.6
57.5
52 .3**
Y/ET
(k g/ha/cm)
N
785
1559
4090
2398
2903
2347
y
(kg/ha)
40.8
57.3
125.5
68 .7
74 .6
73.4**
Y/ET
(kg/ha/cm)
N+P
Evapotranspiration (ET), average yield (Y), and water-nse efficiency (Y/ET) of range vegetation at five locations as affected by nitrogen
and phosphorus fertilizers
Location
Table 3.
:;:_:
�
t
bl
Q
t"
z
"'
f;:
�
""
f:
�
"
z
>
z
'--<
0
c.
�
"
>
z
'"""'
N
°'
Table 4.
Summary of multiple regression analysis, average of five locations
Fertilizer
Control
p
N
N+P
*Y
=
127
JOHNSTON ET AL.-PRECIPITATION AND RANGE VEGETATION
March 1969]
Regression equation*
Y
Y
Y
Y
=
=
=
=
1734.58 + 48.46X12 - l4.46X1
1888.80 + 56 .52X12 - 15.81X1
121.35X2 - 13.09X7
2016.32
889.83 + 194.32X2
+
+ 36.46X,
+ 39.67X,
Standard
error of
estimate
R•
±174.12
±272.00
±558.09
±983.53
0.947
0.902
0.706
0 . 540
Estimated forage yield, kg/ha;
X2 = June precipitation, cm;
X3 = May-June precipitation, cm;
X1 = May-September evaporation, cm;
X12 = Fall soil moisture at 0-60 cm depth, cm.
yield but appeared to be a reflection of the semiarid and subhumid climates of
the study locations. May-September evaporation might reflect also the kind
of season at any study location, high evaporation being characteristic of dry
years, low evaporation of wetter years. Our results are at variance with those
of Smoliak (9) who found a significant (P < 0.01) correlation of May-plus­
June precipitation and yield of vegetation at Manyberries. Smoliak included
in his study yield and seasonal precipitation of the previous year, and yield
and precipitation of the previous October-March period. He did not include
fall soil moisture.
June precipitation, rather than May-June precipitation, influenced the yield
of N+P-treated plots (Table 4). June precipitation and yield of N-treated
plots were significantly correlated (Table 2). These results may reflect the
hastening of growth by the N and N+P treatments. Also, if maturity of stand
is judged by production of seed heads, growth of N- or N+P-treated plots
had progressed further than that of control or P-treated plots at comparable
times. Thus, the water requirements of the N- and N+P-treated plots differed
from those of the control and P-treated plots, and probably were greater early
in the season.
The assumption that consumptive use of water, or evapotranspiration
(ET), was equivalent to spring soil moisture plus seasonal precipitation minus
fall soil moisture (Table 3) seemed to be valid. There was little or no possi­
bility of loss of water from the study locations by either runoff or percolation.
Meteorological records and soil moisture determinations were obtained at each
study location, and hence similar ET values were assigned to all fertilizer
treatments at each location.
Because fertilization increased yields, it also automatically increased the
efficiency of the water used. This finding agrees with other studies (1, 2, 4,
5, 12). Black (1) found that applications of N, with or without P added,
increased water-use efficiency 1.5- to 2.5-fold; he suggested that fertilizers
increased water-use efficiency not only because of greater yields but also be­
cause of greater extraction of soil moisture. Rogler and Lorenz (4) and
Smika et al. (5) reported previously that the rate and depth of root growth
and soil water extraction by range grasses was increased by N fertilization
compared with unfertilized grasses.
The relative yield increase, at the fertilizer levels used in this study,
averaged 110% for P-treated plots, 153% for N-treated plots, and 215% for
128
[Vol. 49
CA"fADIAN JO<:RNAL OF PLANT SCIENCE
N+ P-treated plots, compared with 100% for control plot yields. Relative
increases in water-use efficiency as a result of fertilizer treatments were: con­
trol, 100%; P-treated plots, 111% ; N-treated plots, 157% ; and N+P-treated
plots, 220% .
REFERENCES
1. BLACK, A. L. 1968. Nitrogen and phosphorus fertilization for production of crested
wheatgrass and native grass in northeastern Montana. Agron. J. 60, 213-216.
2. BRIGGS, L. J. and SHANTZ,H. L. 1913. The water requirements of plants.
of the literature. U.S. Bur. Plant Ind. Bull. 285, Washington, D.C.
II. A review
3. JOHNSTON, A., SMOLIAK, S., SMITH, A. D. and LurwicK, L. E. 1967. Improvement of
southeastern Alberta range with fertilizers. Can. J. Plant Sci. 47, 671-678.
4. RoGLER, G. A. and LORENZ, R. J. 1957. Nitrogen fertilization of northern Great Plains
rangelands. J. Range Manage. 10, 156--160.
5. SMIKA, D. E., HAAS, H. J., RoGLER, G. A. and LORENZ, R. J. 1961. Chemical properties
and moisture extraction in rangeland soils as influenced by nitrogen fertilization. J.
Range Manage. 14, 213-216.
6. SMITH, A. D., JoHKSTON, A., LuTWICK, L. E. and SM OLIAK, S.
of fescue grassland vegetation. Can. J. Soil Sci. 48, 125-132.
7.
SMITH, A. D. and LuTwicK, L. E.
J. Plant Sci. 41, 862-864.
1961.
1968.
Fertilizer response
An increasing-rate fertilizer spreader.
Can.
8. SMITH, A. D., MIKKELSEN, T. T. and WALKER, P.H. 1964. An apparatus for weekly
measurement of precipitation and evaporation. Can. J. Plant Sci. 44, 213-215.
9. SMoLIAK, S. 1956. Influence of climatic conditions on forage production of short­
grass rangeland. J. Range Manage. 9, 89-91.
10. SNEVA, F. A.,HYoER, D. N. and COOPER, G. W. 1958. Influence of ammonium nitrate
on the growth and yield of crested wheatgrass on the OregonHigh Desert. Agron. J.
50, 40--44.
11. THOMAS, J. R. and OsENBRUG, A. 1964. Interrelationships of nitrogen, phosphorus,
and seasonal precipitation in the production of bromegrass-crested wheatgrass hay.
U.S. Dep. Agr. Prod. Res. Rep. No. 82, Washington, D.C.
12. VIETS, F. G.
223-264.
1962.
Fertilizers and the efficient use of water.
Advan. Agron. 14,