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Water use by alfalfa, maize, and barley as influenced by available soil water
Agricultural Water Management, 6 (1983) 351--363 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
351
WATER USE BY A L F A L F A , MAIZE, AND BARLEY AS INFLUENCED BY AVAILABLE SOIL WATER
A.S. A B D U L - J A B B A R
I, T.W. S A M M I S ~, D.G. L U G G l, C.E. K A L L S E N
~ and D. S M E A L *
tDepartment of Crop and Soil Sciences, and 2Agricultural Engineering Department, N e w Mexico State University, Box 3268, Las Cruces, N M 88003 (U.S.A.) SSan Juan Branch Station, Farmington, N M (U.S.A.) 4Plains Branch Station, Clovis, N M (U.S.A.) Journal article 958, Agricultural Experiment Station, N e w Mexico State University, Las Cruces, N M 88003, U.S.A. (Accepted 25 January 1983)
ABSTRACT Abdul-Jabbar, A.S., Sammis, T.W., Lugg, D.G., Kallsen, C.E. and Smeal, D., 1983. Water use by alfalfa, maize, and barley as influenced by available soil water. Agric. Water Manage., 6: 351--363. The availability of soil water is one of the most important determinants of crop production. Field studies were conducted to examine the relationships between relative evapotranspiration (E/Ema x) and available water (W) for alfalfa, maize, and barley. Line source sprinkler irrigation systems were used to provide the variations in soil moisture. Actual evapotranspiration (E) was determined using the water balance method. M a x i m u m evapotranspiration (Emax) was the highest E observed a m o n g all irrigation levels. Potential evapotranspiration (E0) was estimated using Penman's equation to characterize the evaporative demand. The results show that the relationships between E/Ema x and W were different for the three crops. For alfalfa, the relationship was dependent on the physical properties of the soil and on E 0. In a clay loam soil, the decline in E from E m a x c o m m e n c e d at a higher value of W than in a sandy loam soil. Furthermore, the rate of decline in E from Emax was dependent on E 0 and was greater as E 0 increased. In the sandy loam soil, the relationship between E/Ema x and W was not dependent on E 0. For maize and barley in clay loam soils, E/Ema x as a function of W was linear, and was not dependent on E 0 . This study was compared to results reported in the literature, and it was hypothesized that differences were related mainly to the way variation in soil moisture was introduced over the measurement period.
INTRODUCTION The relationship between soil water availability and plant water use is needed in many simulation models of plant growth, in which evapotranspiration, photosynthesis, transpiration, and growth are related to soil moisture stress (Hanks, 1974; Arkin et al., 1976; Holt et al., 1976; Selirio et al., 1979).
352 Several models have been proposed which relate plant water use to soil water availability. However, considerable variation exists both in the shape of the relationship and in the point at which soil water begins to limit plant water use. Veihmeyer and Hendrickson (1955) proposed that soil water was equally available from field capacity to permanent wilting point, while Thornthwaite and Mather (1955) suggested that plant water use decreased linearly from the upper to the lower limits of available soil water. Others have proposed a curvilinear relationship (Pierce, 1958; Marlatt et al., 1961). Denmead and Shaw (1962), Holmes and Robertson (1963), and Yang and De Jong (1972) have shown that differences in the relationships between plant water use and available water are mainly due to different evaporative demands and soil physical properties. Kramer (1963) emphasized that it is impossible to predict a level at which soil moisture stress limits plant growth unless evaporative demand, plant species, and stage of growth are known. Penman (1968), in a theoretical study, concluded that the disagreements in the reported relationships between water availability and plant use were mainly due to differences in E0 rates, plant parameters such as root distribution and plant resistance, and the soil hydraulic properties. In most of these studies, the variations in soil moisture were obtained by allowing the soil to dry. This means that the plant physiological processes were monitored only over a given interval of time with an increasing stress rather than over the whole growing season with a more uniform stress. Line source sprinkler irrigation systems provide a wide range of irrigation levels which allow the examination of the relationship between plant water use and available water over the whole growing season with a relatively uniform stress. Accordingly, the objective of this research was to establish the pattern of plant water use as influenced by soil moisture availability for alfalfa, maize, and barley using line source sprinkler systems. MATERIALS AND METHODS The experiment was conducted at three sites in New Mexico, using three crops: maize (Zea mays L.), barley (Hordeum vulgare L.), and alfalfa (Medicago sativa L.). Maize (Northrup King hybrid PX74) was planted at the Plains Branch Experiment Station, 24 km north of Clovis, NM, on 10 April 1980, on 1-m wide beds. Prior to planting, the field was fertilized with 336 kg/ha of N. The plants emerged on 23 April with a density of 58 800 plants per ha. The soil type at the site was a Pullman clay loam (fine-loamy, mixed, thermic Torrefic Palenstall). The field was furrow irrigated until the crop was established. Studies on barley were conducted at two sites. The first was the same site as for the maize. Spring barley (cv. 'Schuyler') was planted on 14 January 1981 in rows spaced 0.18 m apart. It was fertilized with 168 kg/ha of N. The plants emerged on 23 February, with a density of 1 X 106 plants per ha. The
353 second site was located 13 km south of Las Cruces, NM, at the Plant Science Research Center. The soil at the site was an Armijo clay loam (fine, montmorillonitic, thermic Typic Torrert). Spring barley (cv. 'Briggs') was planted on 5 February 1982 in rows spaced 0.18 m apart. It was fertilized with 168 kg/ha o f N and 56 kg/ha of P2Os. The plants emerged on 18 February. Both fields were flood-irrigated until the crop were established. Studies on alfalfa were also conducted at two sites. The first site was located 13 km south o f Las Cruces, NM, near the Plant Science Research Center. The soil at the site was classified as a Belen clay loam (clayey over loamy, montmoriUonitic [calcareous], thermic Vertic Torrifluvent). The field was planted with alfalfa (mixed cv. 'Moapa' and cv. 'Hairy Peruvian') in October 1977, using a grain drill, and was fertilized with 40 kg/ha of N and 103 kg/ha of P. The rows were spaced 0.18 m apart. The field was floodirrigated until the crop was established. The second site was located 11 km southwest of Farmington, NM, at the San Juan Agricultural Experiment Station. The soil at the site was classified as a Wall sandy loam (Typic Calciorthid, coarse loamy mixed, mesic family). The field was planted with alfalfa (cv. 'WL-309') on 22 August 1980, and was fertilized with 20 kg/ha of P. The field was irrigated using a sprinkler ~ystem until the crop was established. Once the crops were established, various levels o f irrigation water were applied, using line source sprinkler systems similar to that described by Hanks et al. (1976). Sprinkler heads (Model 30TNT, Rainbird Co.) were placed 6 m apart in a line and operated at 0.4 MPa pressure. The areas wetted by each sprinkler head overlapped and, therefore, provided uniform gradients of water application from the sprinkler lines to the edges of the plots 15 m away. Water was always applied under calm conditions to reduce wind distortion of the irrigation patterns. The plot size was 30 m X 100 m at each site, with 15 m each side of the sprinkler lines. The amounts of evapotranspiration for the three crops at different irrigation levels were calculated using the water balance m e t h o d : E =I+R
-D
+ AM
(1)
where E = evapotranspiration (ram); I = irrigation (mm); R = rainfall (mm); D = drainage (ram); AM = change in soil moisture, M (ram). Neutron probe access tubes were installed at intervals from the sprinkler lines to the edges of the plots, 1 m apart for alfalfa in the clay loam soil and 2 m for alfalfa in the sandy loam soil and for the maize and barley. Soil moisture (M) was monitored to a depth of 2.1 m for alfalfa and to a depth of 1.5 m for maize and barley, and was determined using a neutron probe every two or three weeks. The a m o u n t of water applied I was measured with catchment cans of 100 m m in diameter, which were placed beside the neutron access tubes. The irrigations were applied at night or early in the morning when the winds were calm and the evaporation losses from the catchment cans were minimized. Two tensiometers were installed at a depth
354 of 0.30 m below the soil surface next to the sprinkler lines. The fields were irrigated whenever the average tensiometer readings reached 0.05 MPa for the clay loam soft, while for the sandy soil the field was irrigated whenever 50% of the available water was depleted. Daffy crop E had been determined from lysimeter data the previous year, and the a m o u n t of water that would replace the water used in crop E was calculated for the period between each irrigation. This a m o u n t was applied at the sprinkler line at each irrigation. Deep drainage D was therefore minimized at the sprinkler line and was negligible at locations away from the sprinkler line. The a m o u n t of rainfall R at each site was measured with rain gauges. R u n o f f was negligible since the water-application rate did not exceed the infiltration rate. The ground water table was 6 m deep at Las Cruces, and below 50 m at the Clovis and Farmington sites, so that upward flow was considered to be negligible. Aboveground biomass for alfalfa was measured at the same locations where E was determined. A detailed description of the operational procedure and harvesting technique for alfalfa was given by Sammis (1981). Grain yields for maize at Clovis and barley at Clovis and Las Cruces were measured on 4 October 1980, 20 July 1981, and 20 June 1982, respectively. A strip of 1 m × 10 m was cut parallel to the sprinkler line at each location where E was determined. Maize was harvested using a plot combine, while barley was harvested using a sickle bar mower and a thresher. Soil moisture retention curves for the softs at each site were determined, using the pressure plate technique (Richards, 1941). Available soil water was then calculated, assuming that soil water above 0.01 MPa and below 1.8 MPa tension was not available for crop use. These limits of tension were based on the examination of soil water measurements over the growing season for the three crops. Water contents at tension 0.01 and 1.8 MPa were 0.43 and 0.18 m3/m 3, respectively, for the clay loam soils near Las Cruces and near Clovis. At Farmington, for the sandy loam soil, the water contents at tension 0.01 and 1.8 MPa were 0.20 and 0.07 m3/m 3, respectively. Available soil water was calculated to a soil depth of 1.05 and 1.5 m for alfalfa in the clay loam and sandy loam soft, respectively, and to 0.5 m for maize and barley, because most of the roots were above these depths (Welbank and Williams, 1968; Robertson et al., 1978; Abdul~Jabbar et al., 1982), and there was no change in soil moisture below these depths. Weather data were collected at a weather station at each site. Daily E0 was calculated using Penman's equation (Penman, 1963). RESULTS AND DISCUSSION The measurement periods of E, E0 and M, the values of Emax and average daffy E0, and the range of M for the three crops during the experimental period are shown in Table I. The value of Emax was the highest E observed among all irrigation levels over the measurement period of E, and Eo and M are averages over the measurement period o f E. The letters A to K in the first
I
Alfalfa, Las Cruces
Alfalfa, Farmington
Maize, Clovis
Barley, Clovis
Barley, Las Cruces
B C
A D E
H F G
I J
K
6.1 7.6
Average E0a (mm/day)
24 April--15 June 1982
14 April--12 May 1981 13 May--24 June 1981
30 May--30 June 1980 1 July--29 July 1980 30 July--3 September 1980
9.1
7.2 9.4
9.8 8.8 7.5
9 April--13 October 1981 6.3 24 July--27 August 1981 7.5 28 August--13 October 1981 4.7
15 April--15 October 1979 15 April--15 October 1980
Measurement period of E, E 0 and M
246
85 332
282 271 264
1480 314 307
1460 1630
Emaxb (mm)
0.28--0.22
0.28--0.24 0.28--0.24
0.33--0.24 0.33--0.22 0.34--0.22
0.16--0.08 0.18--0.07 0.18--0.08
0.34--0.23 0.35--0.23
Range of M a (m3/m 3)
aE 0 and M, averages over the measurement period of E. bEmax, the highest value of E observed among all irrigation levels over the measurement period.
Crop and location
Curve
Clay loam
Clay loam
Clay loam
Sandy loam
Clay loam
Soil type
Measurement periods of evapotranspiration (E), potential evapotranspiration (E0) and soil moisture c o n t e n t (M), the values of Emax and daily average E0, and the ranges of M for alfalfa, maize and barley for different locations and soil types
TABLE
¢J1 C~
356
column represent the curves shown in Figs. 1 to 4. The effect of soil moisture on crop water use is described on a relative basis as shown in Figs. 1 to 4, and, therefore, the absolute values given in Table I may be used to convert the relative value to absolute values.
1.0 ×
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0.6
0.8
PROPORTION AVAILABLE WATER, W Fig. 1. R e l a t i v e e v a p o t r a n s p i r a t i o n (E/Emax) as a f u n c t i o n o f t h e p r o p o r t i o n o f available w a t e r (W) f o r alfalfa in soils o f d i f f e r e n t t e x t u r e s a n d w i t h d i f f e r e n t p o t e n t i a l e v a p o t r a n s p i r a t i o n (E0). A, s a n d y l o a m ( E 0 = 6.3 m m / d a y ) : E/Emax = 0 . 1 8 7 + 2 . 7 0 3 W - 2 . 4 1 9 W 2, r 2 = 0 . 9 4 B, c l a y l o a m ( E 0 = 6.1 m m / d a y ) : E/Ema x = 0 . 2 5 4 + 1.093W, r 2 = 0 . 7 4 C, clay l o a m ( E 0 = 7.6 r a m / d a y ) : E/Emax = - - 0 . 1 1 4 + 1 . 6 4 3 W , r 2 = 0 . 8 2
The relationships between relative evapotranspiration (E/Emax) for alfalfa under different soil textures and E0 levels are shown in Fig. 1. Curve A represents the relationship for the sandy loam soil near Farmington, with an average Eo of 6.3 m m / d a y . Penman's equation was used to calculate the daffy E0 over the measured period of E from 9 April to 13 October 1981. Curves B and C represent the relationships for the clay loam soil near Las Cruces, with average E0 equal to 6.1 and 7.6 m m / d a y , respectively. The measured periods of E and E0 for curves B and C were from 15 April to 15 October in 1979 and 1980, respectively. Curves A, B, and C were statistically different at the 5% level. Under all
357
conditions, E/Emax decreased as W decreased, but the rates of decline were different in each case. For the clay loam soil, with t w o different values of Eo (curves B and C), the point at which E c o m m e n c e d to decline from Emax was not dependent on Eo. From the equations that describe curves B and C, E/Emax was equal to 1.0 when W was equal to 0.68. When W exceeded 0.68, it was assumed that E/Emax was constant and equal to 1.0. This means that Emax was maintained until 0.32 of W was depleted. Below W of 0.68, the reduction in E from Emax was dependent on the existing Eo, with a greater rate of reduction with the higher value of E0. The value 0.68 of W corresponds to a soil water potential of - 0 . 0 4 MPa, according to the moisture retention curve. Van Bavel (1967) found that stomatal control of transpiration from an alfalfa canopy first became noticeable when soil water potential was - 0 . 4 MPa. The relationship between E/Emax and W for the sandy loam soil at Farmington with Eo equal to 6.3 ram/day (curve A) exhibited a longer range of W over which E approached Emax. Then E/Emax decreased rapidly as W decreased further. The formulation of Rijtema and Aboukhaled (1975), as
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_ A _Y.D
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PROPORTIONAVAILABLE WATER, W Fig. 2. Relative evapotranspiration (E/Emax) as a f u n c t i o n o f the p r o p o r t i o n o f available water (W) for alfalfa in a s a n d y l o a m soil w i t h different potential evapotranspiration ( E 0 ) . A , E 0 = 6 . 3 ram/day: E/Ema x = 0 . 1 8 7 + 2 . 7 0 3 W - - 2 . 4 1 9 W 2, r 2 = 0 . 9 4 D, E o = 7.5 ram/day: E/Ema x = 0 . 2 3 6 + 2 . 0 2 4 W - - 1 . 4 0 9 W = , r= = 0 . 9 0 E, E o = 4.7 m m / d a y : E/Ema x = 0 . 3 3 8 + 1 . 4 2 7 W - - 0 . 9 7 5 W ~, r 2 = 0 . 9 0
358
reported by Doorenbos and Kassam (1979), assumed that Emax for alfalfa was maintained with W equal to 6.3 mm/day until 0.45 of W was depleted and then E decreased linearly. They did not specify with which soil texture this was obtained. The relationships between E / E m a x and W for alfalfa growing in a sandy loam soil with different levels of E0 are shown in Fig. 2. Curve A is repeated from Fig. 1 for comparative purposes. Curves D and E represent the relationship over the third and fourth cutting periods which were from 24 July to 27 August and from 28 August to 13 October 1981, respectively. There were no statistical differences among curves A, D and E at the 5% level o f probability. This may be because water is generally more easily moved in sandy textured softs than in clayey soils. The steep reduction in E from Emax did not commence until 0.60 of W was depleted as shown in the following equation. E / E m a x = 0.275 + 1.944 (W) - 1.438 (W) 2
(2)
The coefficient of determination (r 2) was 0.90. Equation 2 represents the pooled data from curves A, D and E. The relationships between E / E m a x and W for maize under three different E0 conditions were linear as shown in Fig. 3. The measured periods of E for
x
1.0
~'~"°Vnj/~
t.u
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0.8
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<~ a.
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I 0.2 PROPORTION
r 0.4 AVAILABLE
i 0.6
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WATER,W
F i g . 3. R e l a t i v e e v a p o t r a n s p i r a t i o n (E/Emax) as a f u n c t i o n o f t h e p r o p o r t i o n o f a v a i l a b l e w a t e r ( W ) f o r m a i z e i n a c l a y l o a m s o i l w i t h d i f f e r e n t p o t e n t i a l e v a p o t r a r m p i r a t i o n (E0). F, E o = 8 . 8 m m / d a y : E/Emax = - - 0 . 0 3 + 1 . 8 5 W , r ~ = 0 . 8 5 G, E 0 = 7.5 m m / d a y : E/Ema x = - - 0 . 0 3 + 1 . 7 3 W , r 2 = 0 . 8 4 H , Eo = 9 . 8 m m / d a y : E/Emax = - - 0 . 0 8 + 1 . 7 5 W , r: = 0 . 8 3
359 curves H, F, and G were 30 May to 30 June, 1 July to 29 July, and 30 July to 3 September 1980, respectively. There were no statistical differences among the relationships at the 5% level. Equation 3, which describes the pooled data from curves F, G, and H, shows that E/Ema x was equal to 1.0 when W was equal to 0.60. Above a W of 0.60 it was assumed that E/Emax was constant and equal to 1.0. Below a W of 0.60, o f the E/Emax decreased linearly as described by equation 3: E/Emax = - 0 . 0 3 2 + 1.73 (W)
(3)
The coefficient of determination (r 2) was 0.80. The relationships between E / E max and W for barley o f t w o locations under three different E0 conditions are shown in Fig. 4. The measured periods for curves I, J and K were 14 April to 12 May and 13 May to 24 June 1981, and 24 April to 15 June 1982, respectively. The Clovis data shown in Fig. 4
../Q • ~
1.0 •
x
J
I
~'/mm
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• K
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0.8
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! 0.2
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PROPORTION A V A I L A B L E WATER,W
Fig. 4. Relative evapotranspiration (E/Emax) as a function of the proportion of available w a t e r (W) f o r b a r l e y in a c l a y l o a m soil w i t h d i f f e r e n t p o t e n t i a l e v a p o t r a n s p i r a t i o n (Eo). I, E 0 = 9.4 r a m / d a y : E/Emax = - - 0 . 1 8 + 2.95W, r 2 = 0.88
J, E 0 = 7.2 ram/day:
E/Emax = --0.21 + 3.09W, r 2 = 0.93
K , Eo = 9.1 r a m / d a y : E/Emax = - - 0 . 0 9 + 2.11W, r 2 = 0.86
360 (Curves I a n d J) are average d a t a at e q u a l distances f r o m t h e line. T h e relat i o n s h i p was i n d e p e n d e n t o f t h e existing E0 at t h e 5% level o f p r o b a b i l i t y . E q u a t i o n 4, w h i c h describes t h e p o o l e d d a t a f r o m curves I, J a n d K, s h o w s t h a t E m a x was m a i n t a i n e d until 0.57 o f W was d e p l e t e d , u n d e r t h e assumpt i o n t h a t E / E m a x was c o n s t a n t a n d e q u a l t o 1.0 at a n d a b o v e a W o f 0.43. B e l o w a W o f 0.43 t h e E / E m a x d e c r e a s e d linearly as d e s c r i b e d b y t h e following e q u a t i o n : E/Ema x = -0.09
+ 2.56 (W)
(4)
T h e c o e f f i c i e n t o f d e t e r m i n a t i o n (r 2) was 0.82. M o g e n s e n ( 1 9 8 0 ) f o u n d t h a t t h e E / E m a x o f spring b a r l e y b e g a n t o decrease w h e n t w o - t h i r d s o f t h e available soil w a t e r was d e p l e t e d . W a t e r - p r o d u c t i o n f u n c t i o n s , t h e r e l a t i o n s h i p b e t w e e n yield and E , w e r e linear o v e r t h e g r o w i n g s e a s o n f o r alfalfa, maize, and b a r l e y as s h o w n in T a b l e II. T h e w a t e r use e f f i c i e n c y or t h e slope o f t h e w a t e r p r o d u c t i o n f u n c t i o n o f t h e spring b a r l e y at Clovis is l o w c o m p a r e d t o t h e w a t e r use efficienc y o f spring b a r l e y g r o w n in o t h e r l o c a t i o n s in N e w M e x i c o ( S a m m i s et al., 1 9 7 9 ; Kallsen et al., 1 9 8 1 ) . T h e climatic c o n d i t i o n s at Clovis are n o t suitable f o r g r o w i n g spring b a r l e y and b a r l e y is n o r m a l l y p l a n t e d o n l y as w i n t e r barley. F i n k n e r ( 1 9 7 1 ) r e p o r t e d t h a t spring b a r l e y yields are n o r m a l l y 50% o f w i n t e r b a r l e y yields. T h u s , t h e w a t e r p r o d u c t i o n f u n c t i o n at Las Cruces is m o r e r e p r e s e n t a t i v e o f t h e w a t e r use e f f i c i e n c y o f spring b a r l e y in N e w Mexico. TABLE II Water-production functions for alfalfa, barley, and maize Description
Water-production function a
Coefficient
of deter-
Range of E b (ram)
mination
Alfalfa, E o = 6.1 mm/day Alfalfa, E o = 7.6 mm/day Alfalfa, E o = 6.3 mm/day Maize
Barley, Las Cruces Barley, Clovis
Y = 0.43 + 0.014 E Y = -0.86 + 0.011 E Y = -6.45 + 0.016 E Grain Y = --8.07 + 0.018 E Grain Y = 2.79 + 0.013 E Grain Y ~- - 2 . 2 2 + 0.0084 E
0.54 0.87* 0.96* 0.91" 0.82* 0.86*
710--1460 370--1630 520- 1480 400--1000 320---570 360--580
ay, yield (t/ha). bE, evapotranspiration (mm). *Significant at the 5% level of probability. P o t e n t i a l yield, or t h e highest p o i n t o n t h e w a t e r p r o d u c t i o n f u n c t i o n , can b e m a i n t a i n e d until t h e W is d e p l e t e d t o t h e p o i n t w h e n E starts t o decrease f r o m E m a x. A f t e r this, yield will b e less w i t h l o w e r E . I t is t h e r e f o r e i m p o r t a n t to define t h e r e l a t i o n s h i p s b e t w e e n E a n d W, a n d t o e s t i m a t e t h e W b e l o w w h i c h E decreases f r o m E m a x .
361 A s u m m a r y o f t h e results o f this s t u d y o n alfalfa a n d m a i z e in c o m p a r i s o n w i t h t h e r e p o r t e d o b s e r v a t i o n s o f D e n m e a d a n d S h a w ( 1 9 6 2 ) , V a n Bavel ( 1 9 6 7 ) , a n d R i t c h i e ( 1 9 7 3 ) are s h o w n in Fig. 5. Part o f Fig. 5 is a d a p t e d f r o m R i t c h i e ( 1 9 7 3 ) . Fig. 5 s h o w s t h e d i f f e r e n t p a t t e r n s o f t h e relative w a t e r use b y alfalfa a n d m a i z e as i n f l u e n c e d b y t h e W in t h e soil. D e n m e a d a n d S h a w m e a s u r e d t h e relative w a t e r use o f a m a i z e c r o p in a silty clay l o a m soil as t h e r a t i o o f a c t u a l t r a n s p i r a t i o n t o t h e t r a n s p i r a t i o n at field c a p a c i t y . T h e E0 f o r t h e i r curves r e p r e s e n t s t h e t r a n s p i r a t i o n at field c a p a c i t y in r a m / d a y . V a n Bavel a n d R i t c h i e m e a s u r e d t h e relative w a t e r use as t h e r a t i o o f actual t o p o t e n t i a l e v a p o r a t i o n , w h e r e p o t e n t i a l e v a p o r a t i o n was c a l c u l a t e d f r o m
® 1.o
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.
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PROPORTION AVAILABLE WATER, W
Fig. 5. Various proposals of the relationship betweenthe relative water use by alfalfa and maize and the proportion of available water. M1, Maize (Denmead and Shaw, 1962), silty clay loam (E o = 6.4 mm/day) M2, Maize (Denmead and Shaw, 1962), silty clay loam (E o = 5.6 mm/day) ®, Maize (Ritchie, 1973), clay (E 0 = 6.5 mm/day) M3, Maize (This study), clay loam (E o = 7.5--9.8 ram/day) AI, Alfalfa (Van Bavel, 1967), clay loam (E o ffi 9.0 ram/day) A2, Alfalfa (This study), clay loam (E o = 7.6 ram/day) A3, Alfalfa (This study), sandy loam (E o = 6.3 ram/day)
362
Penman's equation. Van Bavel's relationship was developed for alfalfa in a clay loam soil with an average E0 equal to 9.0 m m / d a y . Ritchie's relationship was developed for maize in a clay soil with an average E0 equal to 6.5 mm/ day. Ritchie pointed out that the main reason for the variation between his results and those of Denmead and Shaw was due to the experimental technique for measuring the relative water use. Denmead and Shaw measured the relative water use for maize plants grown in containers of 0.75 m 3 in the field, while Ritchie used a weighing lysimeter to measure relative water use for maize. An important factor may also be the way that the variation in soil moisture was introduced over the measurement period. In the three other studies, the variation in soil moisture was obtained by subjecting the crop to a drying cycle after an irrigation. However, the crop responses to a short period of stress would not necessarily be the same as those responses if the crop were subjected to a relatively uniform water stress throughout the growing season, as in this study. Hsiao et al. (1976) emphasized that plant water stress is a dynamic process and depends on the severity, duration, and timing of that stress during the plant ontogeny. ACKNOWLEDGEMENTS
This work was supported in part by Funds provided through the New Mexico Water Resources Research Institute by the United States Department of the Interior, Office of Water Research and Technology, as authorized under the Water Research and Development Act of 1978 Public Law 95-467 under Project Number A-063 N.Mex., B-069 N.Mex., and C-90229. We would also like to acknowledge Jo Anne Guitar's help in collecting the water-production function data.
REFERENCES Abdul-Jabbar, A.S., Sammis, T.W. and Lugg, D.G., 1982. Effect of moisture level on the root pattern of alfalfa. Irrig. Sci., 3: 197--207. Arkin, G.F., Vanderlip, R.L. and Ritchie, J.T., 1976. A dynamic grain sorghum growth model. Trans. ASAE, 19: 622--630. Denmead, O.T. and Shaw, R.H., 1962. Availability of soil water to plants as affected by soil moisture content and meteorological conditions. Agron. J., 54: 385--390. Doorenbos, J. and Kassam, A.H., 1979. Yield response to water. FAO Irrig, Drain. Pap. 33, FAO, Rome, 193 pp. Finkner, M.S., 1971. Performance of small grain cultivars on the High Plains. N.M. Agric. Exp. Stn. Bull. 581, 16 pp. Hanks, R.J., 1974. Model of predicting plant yield as influenced by water use. Agron. J., 66: 660---665. Hanks, R.J., Keller, J., Rasmussen, V.P. and Wilson, G.D., 1976. Line source sprinkler for continuous variable irrigation-crop production studies. Soil Sci. Soc. Am. J., 40: 426--429.
363
Holmes, R.M. and Robertson, G.W., 1963. Application of the relationship between actual and potential evapotranspiration in dryland agriculture. Trans. ASAE, 6: 65--67. Holt, D.A., Dougherty, C.T., Bula, R.J. and Peart, R.M., 1976. Water relations in SIMED, the Purdue model of alfalfa growth. In: K.M. King (Editor), Proc. Symp. on Modeling: Climate-Plant-Softs, Dep. Land Resource Science, 20--21 April 1976, University of Guelph, Ont., pp. 32--45. Hsiao, T.C., Fereres, E., Acevedo, E. and Henderson, D.W., 1976. Water stress and dynamics of growth and yield of crop plants. In: O.L. Lange, L. Kappen and E.D. Schulze (Editors), Water and Plant Life. Problems and Modern Approaches. Ecological Studies, Vol. 19, Springer Verlag, Berlin, pp. 281--305. Kallsen, C., Gregory, E.J. and Sammis, T.W., 1981. Water-use production functions of selected agronomic crops in northwestern N e w Mexico, Phase I. Report No. 137, N e w Mexico Water Resources Research Institute, N.M. State Univ., Las Cruces, N M , 137 pp. Kramer, P.J., 1963. Water stress and plant growth. Agron. J., 55: 31--35. Mogensen, V.O., 1980. Drought sensitivity at various growth stages of barley in relation to relative evapotranspiration and water stress. Agron. J., 72: 1033--1038. Marlatt, W.E., Havens, A.U., Willets, N.A. and Bull, G.D., 1961. A comparison of computed and measured soil moisture under snap beans. J. Geophys. Res., 66: 535--541. Penman, H.L., 1963. Vegetation and hydrology. Tech. C o m m u n . 53, Commonwealth Bur. Soils, Harpanden, Harts., Great Britain, 124 pp. Penman, H.K., 1968. Available and accessible water. In: Trans. 9th International Congress of Soil Science, 1. Am. Elsevier Publ. Co., N e w York, NY, pp. 29--37. Pierce, L.T., 1958. Estimating seasonal and short-term fluctuations in evapotranspiration from m e a d o w crops. Bull. Am. Meteor. Soc., 39: 73--78. Richards, L.A., 1941. A pressure membrane apparatus for soil suction. Soil Sci., 51: 377--386. Rijtema, P.E. and Aboukhaled, A., 1975. Crop water use. In: A. Aboukhaled, A. Afar, A.M~ Balba, B.G. Bisha, L.T. Kadry, P.E. Rijtema and A. Taher (Editors), Research on Crop Water Use, Salt Affected Soils and Drainage in the Arab Republic of Egypt. FAO Regional Office for the Near East, pp. 5--61. Ritchie, J.T.~ 1973. Influence of soil water status and meteorological conditions on evaporation from a corn canopy. Agron. J., 65: 893--897. Robertson, W.K., Hammond, L.C., Johnson, J.T. and Prine, G.M., 1978. R o o t distribution of corn, soybeans, peanuts, sorghum, and tobacco in fine sands. Soil Crop Sci. Soc. Fla. Proc., 38: 12--14. Sammis, T.W., 1981. Yield of alfalfa and cotton as influenced by irrigation.Agron. J., 73: 323--329. Sammis, T.W., Hanson, E.G., Barnes, C.E., Fuehring, H.D., Gregory, E.J., Hooks, R.F., Howell, T.A. and Finkner, M.D., 1979. Consumptive use and yields of crops in New Mexico. Report No. 115. New Mexico Water Resources Research Institute, N.M. State Univ., Las Cruces, NM, 109 pp. Selirio, L.S. and Brown, D.M., 1979. Soil moisture-based simulation of forage yield. Agric. Meteorol., 20: 99--114. Thornthwaite, C.W. and Mather, J.R., 1955. The water budget and its use in irrigation. In: Alfred Stefferud (Editors), Water, the Yearbook of Agriculture, 1955. U.S. Department of Agriculture, Washington, DC, pp. 346--358. Van Bavel, C.H.M., 1967. Changes in canopy resistance to water loss from alfalfa induced by soil water depletion. Agrie. MeteoroL, 4: 165--176. Veihmeyer, F.J. and Hendrickson, A.H., 1955. Does transpiration decrease as soil moisture decreases? Am. Geophys. Union Trans., 36: 425--448. Welbank, P.J. and Williams, E.O., 1968. R o o t growth of a barley crop estimated by sampling with portable powered soil-coring equipment. J. Appl. Ecol., 5: 477--481. Yang, S.J. and De Jong, E., 1972. Effect of aerial environmental and soil water potential on the transpiration and energy status of water in wheat plants. Agron. J., 64: 574-578.
351
WATER USE BY A L F A L F A , MAIZE, AND BARLEY AS INFLUENCED BY AVAILABLE SOIL WATER
A.S. A B D U L - J A B B A R
I, T.W. S A M M I S ~, D.G. L U G G l, C.E. K A L L S E N
~ and D. S M E A L *
tDepartment of Crop and Soil Sciences, and 2Agricultural Engineering Department, N e w Mexico State University, Box 3268, Las Cruces, N M 88003 (U.S.A.) SSan Juan Branch Station, Farmington, N M (U.S.A.) 4Plains Branch Station, Clovis, N M (U.S.A.) Journal article 958, Agricultural Experiment Station, N e w Mexico State University, Las Cruces, N M 88003, U.S.A. (Accepted 25 January 1983)
ABSTRACT Abdul-Jabbar, A.S., Sammis, T.W., Lugg, D.G., Kallsen, C.E. and Smeal, D., 1983. Water use by alfalfa, maize, and barley as influenced by available soil water. Agric. Water Manage., 6: 351--363. The availability of soil water is one of the most important determinants of crop production. Field studies were conducted to examine the relationships between relative evapotranspiration (E/Ema x) and available water (W) for alfalfa, maize, and barley. Line source sprinkler irrigation systems were used to provide the variations in soil moisture. Actual evapotranspiration (E) was determined using the water balance method. M a x i m u m evapotranspiration (Emax) was the highest E observed a m o n g all irrigation levels. Potential evapotranspiration (E0) was estimated using Penman's equation to characterize the evaporative demand. The results show that the relationships between E/Ema x and W were different for the three crops. For alfalfa, the relationship was dependent on the physical properties of the soil and on E 0. In a clay loam soil, the decline in E from E m a x c o m m e n c e d at a higher value of W than in a sandy loam soil. Furthermore, the rate of decline in E from Emax was dependent on E 0 and was greater as E 0 increased. In the sandy loam soil, the relationship between E/Ema x and W was not dependent on E 0. For maize and barley in clay loam soils, E/Ema x as a function of W was linear, and was not dependent on E 0 . This study was compared to results reported in the literature, and it was hypothesized that differences were related mainly to the way variation in soil moisture was introduced over the measurement period.
INTRODUCTION The relationship between soil water availability and plant water use is needed in many simulation models of plant growth, in which evapotranspiration, photosynthesis, transpiration, and growth are related to soil moisture stress (Hanks, 1974; Arkin et al., 1976; Holt et al., 1976; Selirio et al., 1979).
352 Several models have been proposed which relate plant water use to soil water availability. However, considerable variation exists both in the shape of the relationship and in the point at which soil water begins to limit plant water use. Veihmeyer and Hendrickson (1955) proposed that soil water was equally available from field capacity to permanent wilting point, while Thornthwaite and Mather (1955) suggested that plant water use decreased linearly from the upper to the lower limits of available soil water. Others have proposed a curvilinear relationship (Pierce, 1958; Marlatt et al., 1961). Denmead and Shaw (1962), Holmes and Robertson (1963), and Yang and De Jong (1972) have shown that differences in the relationships between plant water use and available water are mainly due to different evaporative demands and soil physical properties. Kramer (1963) emphasized that it is impossible to predict a level at which soil moisture stress limits plant growth unless evaporative demand, plant species, and stage of growth are known. Penman (1968), in a theoretical study, concluded that the disagreements in the reported relationships between water availability and plant use were mainly due to differences in E0 rates, plant parameters such as root distribution and plant resistance, and the soil hydraulic properties. In most of these studies, the variations in soil moisture were obtained by allowing the soil to dry. This means that the plant physiological processes were monitored only over a given interval of time with an increasing stress rather than over the whole growing season with a more uniform stress. Line source sprinkler irrigation systems provide a wide range of irrigation levels which allow the examination of the relationship between plant water use and available water over the whole growing season with a relatively uniform stress. Accordingly, the objective of this research was to establish the pattern of plant water use as influenced by soil moisture availability for alfalfa, maize, and barley using line source sprinkler systems. MATERIALS AND METHODS The experiment was conducted at three sites in New Mexico, using three crops: maize (Zea mays L.), barley (Hordeum vulgare L.), and alfalfa (Medicago sativa L.). Maize (Northrup King hybrid PX74) was planted at the Plains Branch Experiment Station, 24 km north of Clovis, NM, on 10 April 1980, on 1-m wide beds. Prior to planting, the field was fertilized with 336 kg/ha of N. The plants emerged on 23 April with a density of 58 800 plants per ha. The soil type at the site was a Pullman clay loam (fine-loamy, mixed, thermic Torrefic Palenstall). The field was furrow irrigated until the crop was established. Studies on barley were conducted at two sites. The first was the same site as for the maize. Spring barley (cv. 'Schuyler') was planted on 14 January 1981 in rows spaced 0.18 m apart. It was fertilized with 168 kg/ha of N. The plants emerged on 23 February, with a density of 1 X 106 plants per ha. The
353 second site was located 13 km south of Las Cruces, NM, at the Plant Science Research Center. The soil at the site was an Armijo clay loam (fine, montmorillonitic, thermic Typic Torrert). Spring barley (cv. 'Briggs') was planted on 5 February 1982 in rows spaced 0.18 m apart. It was fertilized with 168 kg/ha o f N and 56 kg/ha of P2Os. The plants emerged on 18 February. Both fields were flood-irrigated until the crop were established. Studies on alfalfa were also conducted at two sites. The first site was located 13 km south o f Las Cruces, NM, near the Plant Science Research Center. The soil at the site was classified as a Belen clay loam (clayey over loamy, montmoriUonitic [calcareous], thermic Vertic Torrifluvent). The field was planted with alfalfa (mixed cv. 'Moapa' and cv. 'Hairy Peruvian') in October 1977, using a grain drill, and was fertilized with 40 kg/ha of N and 103 kg/ha of P. The rows were spaced 0.18 m apart. The field was floodirrigated until the crop was established. The second site was located 11 km southwest of Farmington, NM, at the San Juan Agricultural Experiment Station. The soil at the site was classified as a Wall sandy loam (Typic Calciorthid, coarse loamy mixed, mesic family). The field was planted with alfalfa (cv. 'WL-309') on 22 August 1980, and was fertilized with 20 kg/ha of P. The field was irrigated using a sprinkler ~ystem until the crop was established. Once the crops were established, various levels o f irrigation water were applied, using line source sprinkler systems similar to that described by Hanks et al. (1976). Sprinkler heads (Model 30TNT, Rainbird Co.) were placed 6 m apart in a line and operated at 0.4 MPa pressure. The areas wetted by each sprinkler head overlapped and, therefore, provided uniform gradients of water application from the sprinkler lines to the edges of the plots 15 m away. Water was always applied under calm conditions to reduce wind distortion of the irrigation patterns. The plot size was 30 m X 100 m at each site, with 15 m each side of the sprinkler lines. The amounts of evapotranspiration for the three crops at different irrigation levels were calculated using the water balance m e t h o d : E =I+R
-D
+ AM
(1)
where E = evapotranspiration (ram); I = irrigation (mm); R = rainfall (mm); D = drainage (ram); AM = change in soil moisture, M (ram). Neutron probe access tubes were installed at intervals from the sprinkler lines to the edges of the plots, 1 m apart for alfalfa in the clay loam soil and 2 m for alfalfa in the sandy loam soil and for the maize and barley. Soil moisture (M) was monitored to a depth of 2.1 m for alfalfa and to a depth of 1.5 m for maize and barley, and was determined using a neutron probe every two or three weeks. The a m o u n t of water applied I was measured with catchment cans of 100 m m in diameter, which were placed beside the neutron access tubes. The irrigations were applied at night or early in the morning when the winds were calm and the evaporation losses from the catchment cans were minimized. Two tensiometers were installed at a depth
354 of 0.30 m below the soil surface next to the sprinkler lines. The fields were irrigated whenever the average tensiometer readings reached 0.05 MPa for the clay loam soft, while for the sandy soil the field was irrigated whenever 50% of the available water was depleted. Daffy crop E had been determined from lysimeter data the previous year, and the a m o u n t of water that would replace the water used in crop E was calculated for the period between each irrigation. This a m o u n t was applied at the sprinkler line at each irrigation. Deep drainage D was therefore minimized at the sprinkler line and was negligible at locations away from the sprinkler line. The a m o u n t of rainfall R at each site was measured with rain gauges. R u n o f f was negligible since the water-application rate did not exceed the infiltration rate. The ground water table was 6 m deep at Las Cruces, and below 50 m at the Clovis and Farmington sites, so that upward flow was considered to be negligible. Aboveground biomass for alfalfa was measured at the same locations where E was determined. A detailed description of the operational procedure and harvesting technique for alfalfa was given by Sammis (1981). Grain yields for maize at Clovis and barley at Clovis and Las Cruces were measured on 4 October 1980, 20 July 1981, and 20 June 1982, respectively. A strip of 1 m × 10 m was cut parallel to the sprinkler line at each location where E was determined. Maize was harvested using a plot combine, while barley was harvested using a sickle bar mower and a thresher. Soil moisture retention curves for the softs at each site were determined, using the pressure plate technique (Richards, 1941). Available soil water was then calculated, assuming that soil water above 0.01 MPa and below 1.8 MPa tension was not available for crop use. These limits of tension were based on the examination of soil water measurements over the growing season for the three crops. Water contents at tension 0.01 and 1.8 MPa were 0.43 and 0.18 m3/m 3, respectively, for the clay loam soils near Las Cruces and near Clovis. At Farmington, for the sandy loam soil, the water contents at tension 0.01 and 1.8 MPa were 0.20 and 0.07 m3/m 3, respectively. Available soil water was calculated to a soil depth of 1.05 and 1.5 m for alfalfa in the clay loam and sandy loam soft, respectively, and to 0.5 m for maize and barley, because most of the roots were above these depths (Welbank and Williams, 1968; Robertson et al., 1978; Abdul~Jabbar et al., 1982), and there was no change in soil moisture below these depths. Weather data were collected at a weather station at each site. Daily E0 was calculated using Penman's equation (Penman, 1963). RESULTS AND DISCUSSION The measurement periods of E, E0 and M, the values of Emax and average daffy E0, and the range of M for the three crops during the experimental period are shown in Table I. The value of Emax was the highest E observed among all irrigation levels over the measurement period of E, and Eo and M are averages over the measurement period o f E. The letters A to K in the first
I
Alfalfa, Las Cruces
Alfalfa, Farmington
Maize, Clovis
Barley, Clovis
Barley, Las Cruces
B C
A D E
H F G
I J
K
6.1 7.6
Average E0a (mm/day)
24 April--15 June 1982
14 April--12 May 1981 13 May--24 June 1981
30 May--30 June 1980 1 July--29 July 1980 30 July--3 September 1980
9.1
7.2 9.4
9.8 8.8 7.5
9 April--13 October 1981 6.3 24 July--27 August 1981 7.5 28 August--13 October 1981 4.7
15 April--15 October 1979 15 April--15 October 1980
Measurement period of E, E 0 and M
246
85 332
282 271 264
1480 314 307
1460 1630
Emaxb (mm)
0.28--0.22
0.28--0.24 0.28--0.24
0.33--0.24 0.33--0.22 0.34--0.22
0.16--0.08 0.18--0.07 0.18--0.08
0.34--0.23 0.35--0.23
Range of M a (m3/m 3)
aE 0 and M, averages over the measurement period of E. bEmax, the highest value of E observed among all irrigation levels over the measurement period.
Crop and location
Curve
Clay loam
Clay loam
Clay loam
Sandy loam
Clay loam
Soil type
Measurement periods of evapotranspiration (E), potential evapotranspiration (E0) and soil moisture c o n t e n t (M), the values of Emax and daily average E0, and the ranges of M for alfalfa, maize and barley for different locations and soil types
TABLE
¢J1 C~
356
column represent the curves shown in Figs. 1 to 4. The effect of soil moisture on crop water use is described on a relative basis as shown in Figs. 1 to 4, and, therefore, the absolute values given in Table I may be used to convert the relative value to absolute values.
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PROPORTION AVAILABLE WATER, W Fig. 1. R e l a t i v e e v a p o t r a n s p i r a t i o n (E/Emax) as a f u n c t i o n o f t h e p r o p o r t i o n o f available w a t e r (W) f o r alfalfa in soils o f d i f f e r e n t t e x t u r e s a n d w i t h d i f f e r e n t p o t e n t i a l e v a p o t r a n s p i r a t i o n (E0). A, s a n d y l o a m ( E 0 = 6.3 m m / d a y ) : E/Emax = 0 . 1 8 7 + 2 . 7 0 3 W - 2 . 4 1 9 W 2, r 2 = 0 . 9 4 B, c l a y l o a m ( E 0 = 6.1 m m / d a y ) : E/Ema x = 0 . 2 5 4 + 1.093W, r 2 = 0 . 7 4 C, clay l o a m ( E 0 = 7.6 r a m / d a y ) : E/Emax = - - 0 . 1 1 4 + 1 . 6 4 3 W , r 2 = 0 . 8 2
The relationships between relative evapotranspiration (E/Emax) for alfalfa under different soil textures and E0 levels are shown in Fig. 1. Curve A represents the relationship for the sandy loam soil near Farmington, with an average Eo of 6.3 m m / d a y . Penman's equation was used to calculate the daffy E0 over the measured period of E from 9 April to 13 October 1981. Curves B and C represent the relationships for the clay loam soil near Las Cruces, with average E0 equal to 6.1 and 7.6 m m / d a y , respectively. The measured periods of E and E0 for curves B and C were from 15 April to 15 October in 1979 and 1980, respectively. Curves A, B, and C were statistically different at the 5% level. Under all
357
conditions, E/Emax decreased as W decreased, but the rates of decline were different in each case. For the clay loam soil, with t w o different values of Eo (curves B and C), the point at which E c o m m e n c e d to decline from Emax was not dependent on Eo. From the equations that describe curves B and C, E/Emax was equal to 1.0 when W was equal to 0.68. When W exceeded 0.68, it was assumed that E/Emax was constant and equal to 1.0. This means that Emax was maintained until 0.32 of W was depleted. Below W of 0.68, the reduction in E from Emax was dependent on the existing Eo, with a greater rate of reduction with the higher value of E0. The value 0.68 of W corresponds to a soil water potential of - 0 . 0 4 MPa, according to the moisture retention curve. Van Bavel (1967) found that stomatal control of transpiration from an alfalfa canopy first became noticeable when soil water potential was - 0 . 4 MPa. The relationship between E/Emax and W for the sandy loam soil at Farmington with Eo equal to 6.3 ram/day (curve A) exhibited a longer range of W over which E approached Emax. Then E/Emax decreased rapidly as W decreased further. The formulation of Rijtema and Aboukhaled (1975), as
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PROPORTIONAVAILABLE WATER, W Fig. 2. Relative evapotranspiration (E/Emax) as a f u n c t i o n o f the p r o p o r t i o n o f available water (W) for alfalfa in a s a n d y l o a m soil w i t h different potential evapotranspiration ( E 0 ) . A , E 0 = 6 . 3 ram/day: E/Ema x = 0 . 1 8 7 + 2 . 7 0 3 W - - 2 . 4 1 9 W 2, r 2 = 0 . 9 4 D, E o = 7.5 ram/day: E/Ema x = 0 . 2 3 6 + 2 . 0 2 4 W - - 1 . 4 0 9 W = , r= = 0 . 9 0 E, E o = 4.7 m m / d a y : E/Ema x = 0 . 3 3 8 + 1 . 4 2 7 W - - 0 . 9 7 5 W ~, r 2 = 0 . 9 0
358
reported by Doorenbos and Kassam (1979), assumed that Emax for alfalfa was maintained with W equal to 6.3 mm/day until 0.45 of W was depleted and then E decreased linearly. They did not specify with which soil texture this was obtained. The relationships between E / E m a x and W for alfalfa growing in a sandy loam soil with different levels of E0 are shown in Fig. 2. Curve A is repeated from Fig. 1 for comparative purposes. Curves D and E represent the relationship over the third and fourth cutting periods which were from 24 July to 27 August and from 28 August to 13 October 1981, respectively. There were no statistical differences among curves A, D and E at the 5% level o f probability. This may be because water is generally more easily moved in sandy textured softs than in clayey soils. The steep reduction in E from Emax did not commence until 0.60 of W was depleted as shown in the following equation. E / E m a x = 0.275 + 1.944 (W) - 1.438 (W) 2
(2)
The coefficient of determination (r 2) was 0.90. Equation 2 represents the pooled data from curves A, D and E. The relationships between E / E m a x and W for maize under three different E0 conditions were linear as shown in Fig. 3. The measured periods of E for
x
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WATER,W
F i g . 3. R e l a t i v e e v a p o t r a n s p i r a t i o n (E/Emax) as a f u n c t i o n o f t h e p r o p o r t i o n o f a v a i l a b l e w a t e r ( W ) f o r m a i z e i n a c l a y l o a m s o i l w i t h d i f f e r e n t p o t e n t i a l e v a p o t r a r m p i r a t i o n (E0). F, E o = 8 . 8 m m / d a y : E/Emax = - - 0 . 0 3 + 1 . 8 5 W , r ~ = 0 . 8 5 G, E 0 = 7.5 m m / d a y : E/Ema x = - - 0 . 0 3 + 1 . 7 3 W , r 2 = 0 . 8 4 H , Eo = 9 . 8 m m / d a y : E/Emax = - - 0 . 0 8 + 1 . 7 5 W , r: = 0 . 8 3
359 curves H, F, and G were 30 May to 30 June, 1 July to 29 July, and 30 July to 3 September 1980, respectively. There were no statistical differences among the relationships at the 5% level. Equation 3, which describes the pooled data from curves F, G, and H, shows that E/Ema x was equal to 1.0 when W was equal to 0.60. Above a W of 0.60 it was assumed that E/Emax was constant and equal to 1.0. Below a W of 0.60, o f the E/Emax decreased linearly as described by equation 3: E/Emax = - 0 . 0 3 2 + 1.73 (W)
(3)
The coefficient of determination (r 2) was 0.80. The relationships between E / E max and W for barley o f t w o locations under three different E0 conditions are shown in Fig. 4. The measured periods for curves I, J and K were 14 April to 12 May and 13 May to 24 June 1981, and 24 April to 15 June 1982, respectively. The Clovis data shown in Fig. 4
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PROPORTION A V A I L A B L E WATER,W
Fig. 4. Relative evapotranspiration (E/Emax) as a function of the proportion of available w a t e r (W) f o r b a r l e y in a c l a y l o a m soil w i t h d i f f e r e n t p o t e n t i a l e v a p o t r a n s p i r a t i o n (Eo). I, E 0 = 9.4 r a m / d a y : E/Emax = - - 0 . 1 8 + 2.95W, r 2 = 0.88
J, E 0 = 7.2 ram/day:
E/Emax = --0.21 + 3.09W, r 2 = 0.93
K , Eo = 9.1 r a m / d a y : E/Emax = - - 0 . 0 9 + 2.11W, r 2 = 0.86
360 (Curves I a n d J) are average d a t a at e q u a l distances f r o m t h e line. T h e relat i o n s h i p was i n d e p e n d e n t o f t h e existing E0 at t h e 5% level o f p r o b a b i l i t y . E q u a t i o n 4, w h i c h describes t h e p o o l e d d a t a f r o m curves I, J a n d K, s h o w s t h a t E m a x was m a i n t a i n e d until 0.57 o f W was d e p l e t e d , u n d e r t h e assumpt i o n t h a t E / E m a x was c o n s t a n t a n d e q u a l t o 1.0 at a n d a b o v e a W o f 0.43. B e l o w a W o f 0.43 t h e E / E m a x d e c r e a s e d linearly as d e s c r i b e d b y t h e following e q u a t i o n : E/Ema x = -0.09
+ 2.56 (W)
(4)
T h e c o e f f i c i e n t o f d e t e r m i n a t i o n (r 2) was 0.82. M o g e n s e n ( 1 9 8 0 ) f o u n d t h a t t h e E / E m a x o f spring b a r l e y b e g a n t o decrease w h e n t w o - t h i r d s o f t h e available soil w a t e r was d e p l e t e d . W a t e r - p r o d u c t i o n f u n c t i o n s , t h e r e l a t i o n s h i p b e t w e e n yield and E , w e r e linear o v e r t h e g r o w i n g s e a s o n f o r alfalfa, maize, and b a r l e y as s h o w n in T a b l e II. T h e w a t e r use e f f i c i e n c y or t h e slope o f t h e w a t e r p r o d u c t i o n f u n c t i o n o f t h e spring b a r l e y at Clovis is l o w c o m p a r e d t o t h e w a t e r use efficienc y o f spring b a r l e y g r o w n in o t h e r l o c a t i o n s in N e w M e x i c o ( S a m m i s et al., 1 9 7 9 ; Kallsen et al., 1 9 8 1 ) . T h e climatic c o n d i t i o n s at Clovis are n o t suitable f o r g r o w i n g spring b a r l e y and b a r l e y is n o r m a l l y p l a n t e d o n l y as w i n t e r barley. F i n k n e r ( 1 9 7 1 ) r e p o r t e d t h a t spring b a r l e y yields are n o r m a l l y 50% o f w i n t e r b a r l e y yields. T h u s , t h e w a t e r p r o d u c t i o n f u n c t i o n at Las Cruces is m o r e r e p r e s e n t a t i v e o f t h e w a t e r use e f f i c i e n c y o f spring b a r l e y in N e w Mexico. TABLE II Water-production functions for alfalfa, barley, and maize Description
Water-production function a
Coefficient
of deter-
Range of E b (ram)
mination
Alfalfa, E o = 6.1 mm/day Alfalfa, E o = 7.6 mm/day Alfalfa, E o = 6.3 mm/day Maize
Barley, Las Cruces Barley, Clovis
Y = 0.43 + 0.014 E Y = -0.86 + 0.011 E Y = -6.45 + 0.016 E Grain Y = --8.07 + 0.018 E Grain Y = 2.79 + 0.013 E Grain Y ~- - 2 . 2 2 + 0.0084 E
0.54 0.87* 0.96* 0.91" 0.82* 0.86*
710--1460 370--1630 520- 1480 400--1000 320---570 360--580
ay, yield (t/ha). bE, evapotranspiration (mm). *Significant at the 5% level of probability. P o t e n t i a l yield, or t h e highest p o i n t o n t h e w a t e r p r o d u c t i o n f u n c t i o n , can b e m a i n t a i n e d until t h e W is d e p l e t e d t o t h e p o i n t w h e n E starts t o decrease f r o m E m a x. A f t e r this, yield will b e less w i t h l o w e r E . I t is t h e r e f o r e i m p o r t a n t to define t h e r e l a t i o n s h i p s b e t w e e n E a n d W, a n d t o e s t i m a t e t h e W b e l o w w h i c h E decreases f r o m E m a x .
361 A s u m m a r y o f t h e results o f this s t u d y o n alfalfa a n d m a i z e in c o m p a r i s o n w i t h t h e r e p o r t e d o b s e r v a t i o n s o f D e n m e a d a n d S h a w ( 1 9 6 2 ) , V a n Bavel ( 1 9 6 7 ) , a n d R i t c h i e ( 1 9 7 3 ) are s h o w n in Fig. 5. Part o f Fig. 5 is a d a p t e d f r o m R i t c h i e ( 1 9 7 3 ) . Fig. 5 s h o w s t h e d i f f e r e n t p a t t e r n s o f t h e relative w a t e r use b y alfalfa a n d m a i z e as i n f l u e n c e d b y t h e W in t h e soil. D e n m e a d a n d S h a w m e a s u r e d t h e relative w a t e r use o f a m a i z e c r o p in a silty clay l o a m soil as t h e r a t i o o f a c t u a l t r a n s p i r a t i o n t o t h e t r a n s p i r a t i o n at field c a p a c i t y . T h e E0 f o r t h e i r curves r e p r e s e n t s t h e t r a n s p i r a t i o n at field c a p a c i t y in r a m / d a y . V a n Bavel a n d R i t c h i e m e a s u r e d t h e relative w a t e r use as t h e r a t i o o f actual t o p o t e n t i a l e v a p o r a t i o n , w h e r e p o t e n t i a l e v a p o r a t i o n was c a l c u l a t e d f r o m
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PROPORTION AVAILABLE WATER, W
Fig. 5. Various proposals of the relationship betweenthe relative water use by alfalfa and maize and the proportion of available water. M1, Maize (Denmead and Shaw, 1962), silty clay loam (E o = 6.4 mm/day) M2, Maize (Denmead and Shaw, 1962), silty clay loam (E o = 5.6 mm/day) ®, Maize (Ritchie, 1973), clay (E 0 = 6.5 mm/day) M3, Maize (This study), clay loam (E o = 7.5--9.8 ram/day) AI, Alfalfa (Van Bavel, 1967), clay loam (E o ffi 9.0 ram/day) A2, Alfalfa (This study), clay loam (E o = 7.6 ram/day) A3, Alfalfa (This study), sandy loam (E o = 6.3 ram/day)
362
Penman's equation. Van Bavel's relationship was developed for alfalfa in a clay loam soil with an average E0 equal to 9.0 m m / d a y . Ritchie's relationship was developed for maize in a clay soil with an average E0 equal to 6.5 mm/ day. Ritchie pointed out that the main reason for the variation between his results and those of Denmead and Shaw was due to the experimental technique for measuring the relative water use. Denmead and Shaw measured the relative water use for maize plants grown in containers of 0.75 m 3 in the field, while Ritchie used a weighing lysimeter to measure relative water use for maize. An important factor may also be the way that the variation in soil moisture was introduced over the measurement period. In the three other studies, the variation in soil moisture was obtained by subjecting the crop to a drying cycle after an irrigation. However, the crop responses to a short period of stress would not necessarily be the same as those responses if the crop were subjected to a relatively uniform water stress throughout the growing season, as in this study. Hsiao et al. (1976) emphasized that plant water stress is a dynamic process and depends on the severity, duration, and timing of that stress during the plant ontogeny. ACKNOWLEDGEMENTS
This work was supported in part by Funds provided through the New Mexico Water Resources Research Institute by the United States Department of the Interior, Office of Water Research and Technology, as authorized under the Water Research and Development Act of 1978 Public Law 95-467 under Project Number A-063 N.Mex., B-069 N.Mex., and C-90229. We would also like to acknowledge Jo Anne Guitar's help in collecting the water-production function data.
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