Irrigation management in arid areas affected by surface crust

Agricultural Water Management 38 (1998) 21±32

Irrigation management in arid areas affected by surface crust A.M. Abu-Awwad*,1 Faculty of Agriculture, University of Jordan, Amman, Jordan Accepted 3 June 1998

Abstract The effects of supplemental irrigation and irrigation practices on soil water storage and barley crop yield were studied for a crust-forming soil at the University of Jordan Research Station near Al-Muwaqqar village during the 1996/97 growing season. An amount of 0.0, 48.9, 73.3, 122.2 and 167 mm supplemental irrigation water were applied. The 48.9, 73.3 and 122.2 mm applications were applied through surface irrigation into furrows with blocked ends, and the 0.0 and 167 mm applications via sprinkler irrigation. The greatest water infiltration and subsequent soil storage was achieved with the 122.2 mm application followed by the 73.3 mm irrigation, both surface applied. Application efficiency (the fraction of applied water that infiltrated into the soil and stored in the 600 mm soil profile) and soil water storage associated with supplemental blocked furrow irrigation was significantly greater than with supplemental sprinkler irrigation. For arid zone soil, which has little or no structural stability, application of supplemental irrigation water via short, blocked-end furrows prevents runoff and increases the opportunity time for infiltration, thereby increasing the amount of applied water that is infiltrated into the soil and stored in the soil profile. Supplemental irrigation, applied by a low-rate sprinkler system, was not as effective because of the low infiltration rates that resulted from the development of a surface throttle due to dispersion of soil aggregates at the soil surface. The differences in stored water had a significant effect on grain and straw yields of barley. Without supplemental irrigation, barley grain and straw yields were zero in natural rainfall cultivation with a total rainfall of 136.5 mm. Barley yields in the control treatment, with a 167 mm supplemental sprinkler irrigation were low being 0.19 and 1.09 ton/ha of barley grain and straw, respectively. Supplemental irrigation through blocked-end furrows increased barley grain and straw yields significantly compared with supplemental sprinkler irrigation to a maximum of 0.59 and 1.8 ton/ha, respectively. The improvement coming from the increased water storage associated with furrows. Since irrigation water is very limited if available, farmers are encouraged to form such furrows for reducing runoff from rainfall thereby increasing * Fex: +96-265355578. 1 Associate Professor, Department of Agricultural Resources and Environment, Faculty of Agriculture. 0378-3774/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 9 8 ) 0 0 0 5 6 - 0

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the amount of water available for forage and field crop production. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Surface crust; Blocked-end furrows; Sprinkler; Supplemental irrigation

1. Introduction The problem of water shortage in arid zones is one of low annual rainfall. In arid and semi-arid regions, rainfalls are characterized as erratic in distribution and of highly variable intensity. In the presence of soil surface crusts and the thin vegetation covers in such areas rain water losses due to evaporation and surface runoff are very high. In such regions, soils are characterized by very low crop production, resulting from droughts and deteriorating soil properties (weak aggregate stability, high silt content and strong surface crust). Critchley and Siegert (1991) indicated that in arid regions rain-fed agriculture is not feasible without the use of water harvesting. Cultivating such areas depends on solving problems associated with water resources and the deterioration of soil properties. Water harvesting has been used for many years in different areas in the world to solve the problem of irrigation water shortages (Arnon, 1972; Boers and Ben-Asher, 1982; Boers et al., 1986; Brunis et al., 1986). Deteriorated soil properties need special management depending on the specific soil problem. One of the problems is soil crust formation which reduces crop production and water infiltration causing loss of valuable water and soil erosion. The susceptibility to sealing is common in many arid and semi-arid soils, where the soil surface is characterized by low organic matter, high silt contents and low aggregate stability (El-Swaify et al., 1984; Arshad and Mermut, 1988). Over one million hectares of irrigated land in California alone are affected by slow water infiltration problem (Oster and Singer, 1984). The reason behind this slow water penetration is that the surface crust has very low hydraulic conductivity (Stroosnijder and Hoogmoed, 1984). The skin seal (crust) has 2000 times lower permeability than the underlying soil layers (McIntyre, 1958). The infiltration rate into uncrusted soil, as an example, was 8000 mm/day, while the presence of only 0.1 mm thick crust reduced that rate to 700 mm/day (Falayi and Bouma, 1975). The soil crusting phenomenon attracted the concern of many researchers for many years, due to its importance and its significant effect on land use. This phenomenon hinders the agricultural expansion and food production. Researchers studied and described soil crust formation throughout the world (McIntyre, 1958; Falayi and Bouma, 1975; Chen et al., 1980; Onofiok and Singer, 1984). Based on their studies on crusts and understanding their formation they tried to find different solutions for the adverse effect of soil surface crusts on crop production, soil water storage, and soil erosion. Disadvantages of reduced infiltration rate are the adverse effects on the efficiency of rainfall and irrigation water applied by overhead irrigation systems (Hoogmoed and Stroosnijder, 1984). Infiltration and runoff are largely related. Water which does not infiltrate into the soil surface will flow as surface runoff causing soil erosion (Bradford et al., 1987; Remley and Bradford, 1989).

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The aim of tillage in crusted soils is to reduce surface runoff through contour ploughing, strip cropping, surface mulching and minimum tillage (Mallett et al., 1981). Conventional tillage has only a short-lived positive effect on crusted soils which ends with the first rain shower (Stroosnijder and Hoogmoed, 1984). It was found that tie ridging or basin tillage practices increased soil water storage more than simply breaking the soil surface crust. Soil moisture storage increased by applying contour furrowing at 1±1.5 m intervals, and the yield of perennial grasses increased to about 560 kg/ha (Branson et al., 1966). In the desert grassland of southern Arizona, furrowing produced 2.5 times more grass than the adjacent untreated area, while soil moisture storage was 66 mm in the furrowed area compared with only 30 mm in untreated soil (Brown and Everson, 1952). Frequent wetting and drying of the soil surface tends to soften and disintegrate the surface crust (Salih and Maulood, 1987), by the dissolving and decomposing of soil compounds. Some of these compounds such as CaCO3 and CaSO4 acts as cementing agents and introduce changes in soil structure which can account for lowering soil strength (Kemper et al., 1974). As a result, frequent irrigation had a significant positive effect on seedling emergence, shoot dry weight and height of seedlings (Salih and Maulood, 1985). Al-Muwaqqar watershed is typical of large areas of Jordan, where overgrazing and indiscriminate cultivation have degraded the land, destroyed the vegetation and caused erosion of fertile top soil. The challenge of the surface crust at Al-Muwaqqar area attracted the concern of many researchers, due to its significant effect on land use. AbuAwwad and Shatanawi (1997) selected three micro-watersheds to investigate runoffrainfall characteristics indicated that soil water storage and infiltration were very low and almost negligible for the third and forth soil layers owing to the presence of the soil surface crust. In other field experiment, Akasheh and Abu-Awwad (1997) studied the effects of sprinkler irrigation and soil surface management on soil water storage and barley yield in soils affected by surface crust. They found that with sprinkler irrigation, managing soil surface by constructing furrows, furrows within basin or basins and/or managing water application by dividing the required amount of irrigation water equally between two or three applications separated by 48 h significantly increased soil water storage and consequently barley yield. The effects of soil surface crust and rainfall on water infiltration and distribution in the natural soil profile and the possibility of improving water infiltration and redistribution using sand columns (about 55 mm holes or pits from the soil surface to a depth of 600 mm, filled with sand) were investigated by Abu-Awwad (1997). He found that sand columns at appropriate spacing greatly improved water storage efficiency, particularly at depth, where the stored water is protected from evaporation. Studies indicated that with a maximum rainfall intensity of 3.3±4.4 mm/h. 35.4% of effective rainfall was lost in surface runoff (Shatanawi and Abu-Awwad, 1994). Al-Qinna (1997) indicated that even with the low sprinkler application rate of 6.2 mm/h, on these very weakly structured soils, the rapid wetting of the dry soil, whether it be by ponding or sprinkling, will cause much the same degree of structure breakdown and the final infiltration rate will be the same being 3.2 mm/h. At the Al-Muwaqqar soil, slaking of the surface soil aggregate may take place, when electrolyte concentration of the irrigation water was higher than the corresponding critical salt coagulation concentration (CCC) of the soil±clay (Abu-Sharar and Salameh, 1995). They also suggested that clay

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dispersion and the subsequent surface crust formation may take place, when electrolyte concentration of the irrigation water drops well below the corresponding CCC of the soil± clay. Jordan, which requires increased food production for its increasing population, has to extend its agricultural area, especially in areas which receive a rainfall between 100 and 200 mm (about 13% of Jordan's area). This area has a feasible potential for agricultural production, but suffers from a soil surface crust problem which hinders the utilization of this area for forages and crop production. Proper management in these areas in increasing the crop production, might lead Jordan towards food security and greater saving of money. Therefore, the objective of this research project was to study the effects of supplemental irrigation and irrigation management practices on soil water storage and barley crop yield. 2. Material and methods A field experiment was conducted during the 1996/97 (18 November 1996 to 7 June 1997) growing season at the University of Jordan Research Station located about 45 km southeast of Amman, near Al-Muwaqqar village. The area is characterized by irregular, sporadic and unpredictable rainfall. The average annual rainfall during 1986±96 was 125 mm. Rainfall occurs in the winter season (November±April) in the form of intensive storms of short duration, which cause high rates of surface runoff owing to the presence of a soil surface crust. January is the coldest month of the year with mean minimum and maximum temperatures of 38C and 138C, respectively, while August is the hottest month with mean minimum and maximum temperatures of 178C and 338C, respectively. Mean relative humidity varies from 45% (August) to 70% (January). Generally, the area is characterized by a weak vegetation cover and aggregate stability, soil surface of high silt content, strong structural surface crust of an average 2 mm thick and 0.625 h. hydraulic resistance. Also, a restricting pan layer exist at a depth of 20±30 cm. The soil classification of this area is Fine silty, mixed, thermic, Typic Paleorthid with a slope of less than 1% (Taimeh, 1989). Some physical and chemical properties of the experimental site soil are presented in Table 1. Field capacity and permanent wilting point were determined in the laboratory for each soil layer using undisturbed soil samples using the ceramic plate apparatus at 0.3 and

Table 1 Physical and chemical properties of the soil in the experimental site Horizon

Depth (mm)

Sand (%)

Silt (%)

Caly (%)

SG

ECe (dS/m)

FC (v%)

PWP (v%)

MWD (mm)

A1 BA Bw Bw

00±150 150±300 300±450 450±600

3.3 4.1 5.2 7.0

66.7 62.6 53.8 50.8

30.0 33.3 41.0 42.2

1.18 1.38 1.37 1.34

1.50 1.50 1.65 1.60

26 28 29 28

15 17 18 17

0.35

SG: Specific gravity, ECe: Paste extract electrical conductivity, FC: Field capacity, PWP: Permanent wilting point, MWD: Aggregate stability mean weight diameter.

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15 bars, respectively. Field capacity for the first soil layer was also determined and checked in the field. Aggregate stability mean weight diameter was also determined in the laboratory by wet sieving. Planting and fertilization (Diammonium phosphate: 46:20:0) were done at the same time using hand broad casting to plant barley (Hordeum vulgare L. CV. Rum) at a rate of 100 kg/ha. Also, another 50 kg/ha diammonium phosphate was applied at the tillering stage. The experimental design was completely randomized. The experiment consisted of five treatments: R: rain-fed cultivation with natural soil surface and 0.0 supplemental irrigation; S: rain-fed cultivation with natural soil surface and 167 mm supplemental sprinkler irrigation; F1: two blocked furrows at 4 m intervals; F2: three blocked furrows at 2 m intervals; F3: five blocked furrows at 1 m interval, with twelve replicates. Blocked furrows (trenches) about 250 mm deep and 300 mm wide along the plot were established perpendicular to the slope direction. Each plot was 66 m2 in size. For F1, F2 and F3 treatments, supplemental irrigation water was applied separately to each plot using blocked end furrow surface irrigation with an average discharge rate of 0.22 m3/h per furrow. While, in S treatment supplemental irrigation water was applied via sprinkler irrigation with an average application rate of 8 mm/h. The required amount of irrigation water was applied four times during the growing season (11 and 29 January, 31 March and 8 April, 1997) to bring the soil water content near field capacity in the top 300 mm. The source of water was from small reservoirs created by earth dams constructed across a seasonal water coarse. Irrigation water quality used in this study was same for all treatments. The average pH, EC (electrical conductivity), and sodium adsorption ratio (SAR) values of the supplemental irrigation water used in the experiment were 7.8, 2.2 dS/m, 4.4, respectively, (no restriction for use in irrigation, according to the guidelines for infiltration of water quality for irrigation (Ayers and Westcot, 1985)). Three access tubes were installed in each plot to a depth of 600 mm. Soil moisture content was measured with a neutron probe at depth increments of 150 mm starting at 75 mm from the soil surface and going down to a depth of 525 mm. Soil moisture in the surface layer (0±150 mm) was determined using the gravimetric method. The amount of water stored in the soil profile as a result of rainfall and/or irrigation was calculated from the soil moisture reading. The increase in soil moisture in a given layer after rainfall or irrigation was calculated as SWS ˆ …v2 ÿ v1 †  D=100 where SWS is the increase in soil water storage (mm). v1 and v2 are the volumetric soil water content (%) before and within 24 h after water application (rainfall or irrigation), respectively. D is the thickness of soil layer (mm). Seasonal soil water storage was calculated by summing the increase in soil water storage throughout the whole growing season. Runoff water for each rain and/or irrigation event (in R and S treatments) was calculated as Rn ˆ WA ÿ SWS ÿ Ews where Rn is the runoff depth (mm). WA is the water depth received (rain and/or irrigation) in mm, and SWS is the amount of water stored in the soil profile (mm). Ews is the evaporation during precipitation or irrigation event (mm). For each rain and/or irrigation event, evaporation from wet soil surface was calculated using a Class A pan dry

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fetch installed on the experimental site as Ews ˆ Ep  Kp  Ks  …1 ÿ …tw =td †1=2 † (after Allen and Puritt, 1991)where Ews is the evaporation from a wet soil surface (mm/ day), Ep is the pan evaporation (mm/day), Kp is the pan coefficient, a function of wind speed, relative humidity and fetch. Estimated Kp values ranged from 0.52 to 0.7. Ks is the soil evaporation factorˆ1.0 for sprinkler and rainfall. While in the furrow treatments, evaporation from a wet soil surface (Ews) was calculated as Ews ˆ WA ÿ SWS Barley consumptive use (evapotranspiration ˆ evaporation ‡ transpiration) was calculated as CU ˆ WA ÿ Rn 
SW where CU is the barley consumptive use depth (mm), WA is the measured water applied (precipitation and irrigation) in mm and
SW is the change in soil water content in the 600 mm root zone depth in mm. Barley grain and straw yields from the 36 m2 plot were harvested and measured at the end of the growing season. Rainfall amounts were recorded using a rain gauge recorder on the experimental site. 3. Results and discussion 3.1. Soil water storage and distribution Table 2 indicates that the total amount of water stored in F3 (1 m furrow spacing) treatment was significantly higher than F2 (2 m furrow spacing), F1 (4 m furrow spacing) and S (control) treatments. Since the discharge introduced to each furrow was constant (0.22 m3/h), the amount of irrigation water added to each plot treatment was different. Amounts of supplemental irrigation were 48.9, 73.3 and 122.2 mm in F1, F2 and F3 treatments, respectively, and 167 mm in the sprinkler applied (S) treatment. With blocked-end furrow surface irrigation, the application efficiency (fraction of the applied supplemental irrigation water that infiltrated into the soil and stored in the top 600 mm of Table 2 Soil water budget as influenced by furrow spacing and irrigationa Treatment

Supplemental irrigation (mm)

Wet surface evaporation (mm)

Surface runoff (mm)

Soil water Application storage efficiency (mm/600 mm) (%)

F1: 4 m F2: 2 m F3: 1 m S: Sprinkler (control)

48.9 73.3 122.2 167.0

14.3 10.5 15.1 19.2

0 0 0 104.0

34.6 62.8 107.1 43.1

c b a c

70.8 85.7 87.6 25.8

a Values followed by the same letter are not significantly different according to Duncan's multiple range test at 5% confidence level. Coefficient of variation (CV)ˆ19.3 and regression of correlation (r2)ˆ0.86.

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the soil profile) improved from about 26% in the S (via sprinkler irrigation) treatment to about 71%, 86% and 88% in F1, F2 and F3 (via blocked-end furrow irrigation) treatments, respectively, owing largely to the elimination of surface runoff. Also, soil moisture measurements indicated that soil water content in the third (300±450 mm) and the forth (450±600 mm) soil layers never approach their field capacity, besides there was no ground water table buildup on the impermeable layer (100±150 mm hard petrocalcic horizon thick) at the bottom of the soil profile which eliminate the possibility of any deep percolation. Thus, the differences between the measured water increase in the top 600 mm soil profile and the amount of applied water were largely due to soil surface evaporation and barley transpiration during the 24 h period between soil moisture measurements before and after each irrigation event. Increasing the number of furrows per plot increased the amount of water added and the application efficiency. This could only be due to a reduction in the evaporation losses since runoff and deep percolation losses were negligible owing to the blocked-end furrows and the presence of an impermeable layer at the bottom of the 600 mm soil profile. The general soil water storage distribution pattern (water stored in each soil layer as a percent of total water stored in the top 600 mm of the soil profile) in these crusted soils was about 68.8%, 18.4%, 8.4% and 4.4% for soil layers 0±150, 150±300, 300±450 and 450±600 mm, respectively, following sprinkler irrigation. While, with blocked end furrow surface irrigation, the equivalent pattern was about 27.6%, 33.7%, 24.0% and 14.7% for the same soil layers, respectively. In blocked-end furrow treatments, total soil water storage was significantly higher with the 122.2 mm supplemental irrigation than with the 73.3 and 48.9 mm supplemental irrigation water treatments owing to the variation in the amount of supplemental irrigation applied. However, soil water storage was significantly lower in the 167 mm supplemental sprinkler irrigation treatment than in the 73.3 and 122.2 mm supplemental furrow irrigation treatments, but was not significantly different from the 48.9 mm supplemental furrow treatment (Table 2). Fig. 1 illustrates soil water storage distribution in the different soil layers as influenced by irrigation management practices. In the first soil layer (0±150 mm), soil water storage associated with the 167 mm sprinkler (S) treatment was not significantly different from that with the 122.2 mm furrow (F3) treatment, but was significantly greater than that in the 48.9 (F1) and 73.3 mm (F2) furrow treatments owing to the high amount of supplemental water applied via sprinkler irrigation. For the second soil layer (150± 300 mm) soil water storage in S treatment was very low being 7.9 mm/150 mm. Blockedend furrows increased soil water storage significantly compared with that in the S treatment to a maximum of 35.6 mm/150 mm in F3 treatment. With sprinkler irrigation, soil surface crust was the determinant factor for infiltration and subcrust permeability. But, blocked-end furrows allow to bypass the surface crust, thereby the pan layer at 200± 300 mm soil depth was the determinant factor for infiltration and subsoil permeability. With blocked-end furrow irrigation, soil water storage in F1, F2 and F3 treatments were significantly higher than soil water storage in S treatment, in the third soil layer (300± 450 mm). Soil water storage were 7.3, 16.0 and 27.3 mm/150 mm with the 48.9, 73.3 and 122.2 mm furrow irrigation treatments, respectively, significantly higher than 3.6 mm/ 150 mm with the 167 mm supplemental sprinkler irrigation treatment. The results were

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Fig. 1. Soil water storage in the four soil layers as influenced by furrow spacing and sprinkler treatments.

similar in the fourth soil layer (450±600 mm), the same supplemental furrow irrigation treatments being 5.2, 8.9, and 15.9 mm/150 mm, respectively, significantly higher than 1.9 mm/150 mm in the 167 mm supplemental sprinkler irrigation treatment. Thus, short blocked-end furrows through eliminating surface runoff and allowing water to infiltrate slowly through the hard surface crust over a longer time period are much superior to sprinkler application. Also, furrows increased soil surface area for infiltration inside the

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Table 3 Estimated seasonal consumptive use and barley yield as affected by furrow treatments and supplemental irrigationa Treatment

R

F1

F2

F3

S

Rainfall (mm) Irrigation (mm) Change in soil water storage (mm)b Seasonal consumptive use (mm) Barley grain yield (ton/ha) Barley straw yield (ton/ha) Water use efficiency (kg grain/mm/ha)

136.5 0.0 3.2 55.6 0.0 0.0 0.0

136.5 48.9 ÿ4.4 181.0 c 0.36 b 1.05 b 1.99 b

136.5 73.3 ÿ7.6 202.2 b 0.49 a 1.33 b 2.42 a

136.5 122.2 ÿ13.5 245.2 a 0.59 a 1.80 a 2.40 a

136.5 167 2.5 130.0 d 0.19 c 1.09 b 1.46 c

e d c d

a

Values followed by the same letter in the same row are not significantly different according to Duncan's multiple range test at 5% confidence level. b Soil water contribution in barley consumptive use (
SW)ˆinitial soil water content (at planting date)ÿfinal soil water content (at harvest date).

furrows occurs in two dimensions (vertical and horizontal) and through the cracks formed inside the furrow when it gets dry. These results are in agreement with the finding of AbuAwwad (1997), Akasheh and Abu-Awwad (1997), and Abu-Awwad and Shatanawi (1997). They indicated that soil water storage and infiltration were very low and almost negligible for the third and fourth layers owing to the presence of the surface crust and the pan layer at a depth of 200±300 mm, and the low surface infiltration and permeability using sprinkler irrigation or natural precipitation. 3.2. Barley yield and consumptive use Without supplemental irrigation, barley grain and straw yields in natural rainfall cultivation (R) treatment were zero with a total rainfall of 136.5 mm for untreated areas (Table 3). Table 3 shows that barley grain yields in F3 and F2 furrow treatments were not significantly different, but were significantly different from barley grain yields in F1, S and R treatments. The F3 furrow treatment produced significantly higher barley grain yield (0.59 ton/ha) than barley grain yield in F1 (0.36 ton/ha) and S (0.19 ton/ha) treatments. Also, F2 furrow treatment produced 0.49 ton/ha significantly higher barley grain yield compared with 0.36 and 0.19 ton/ha in F1 and S treatments, respectively. Barley straw yield in the F3 furrow treatment was significantly higher than in F2, F1, S and R treatments. The F3 furrow treatment produced 1.8 ton/ha significantly higher barley straw yield as compared with 1.33, 1.05 and 1.09 ton/ha barley straw yields in F2, F1 and S treatments, respectively. While, barley straw yields in F2, F1 and S treatments were not significantly different but significantly higher than barley straw yield in the R treatment. Results show that supplemental irrigation is a must for barley production in areas where rainfall is limited. Owing to the presence of a surface crust and low infiltration rate the usual positive benefits of sprinkler supplemental irrigation were limited. The 167 mm supplemental sprinkler irrigation produced only 0.19 and 1.09 ton/ ha barley grain and straw yields, respectively. Blocked-end furrow surface irrigation improved barley grain and straw yields significantly even with limited amount of supplemental irrigation as compared to supplemental sprinkler irrigation. This might be

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owing to the fact that application of supplemental irrigation water via short, blocked-end furrows prevents runoff and increases the opportunity time for infiltration, thereby increasing the amount of applied water that is infiltrated into the soil and stored in the soil profile. These results are in agreement with Brown and Everson (1952) who found that a furrow soil surface treatment produced 2.5 times more grass than adjacent untreated range land. Akasheh and Abu-Awwad (1997) indicated that with sprinkler irrigation, barley grain yield significantly increased from 0.51 in the control treatment to 1.53 ton/ha in the furrow soil surface treatment. In general, barley grain yields for this season (1996/ 97) were very low in all treatments as compared to other years owing to a severe frost incident that hit the region during the filling stage for the period 12±14 April, 1997. Barley consumptive use were 55.6, 181.0, 202.2, 245.2 and 130.0 mm in R, F1, F2, F3 and S treatments, respectively. With blocked-end furrows, increasing amount of supplemental irrigation water from 48.9 in F1 treatment to 73.3 mm in F2 treatment and to 122.2 mm in F3 treatment significantly increased barley consumptive use from 181 in F1 treatment to 202.2 mm in F2 treatment and to 245.2 mm in F3 treatment. With the 167 mm supplemental sprinkler irrigation barley consumptive use was only 130 mm and was significantly lower than barley consumptive use associated with that in F1, F2 and F3 treatments, but was significantly higher than consumptive use in R treatment (Table 3). This result indicates that amount of rainfall and available soil water were limited and addition of irrigation water increases both barley consumptive use and yield. With supplemental irrigation, Akasheh and Abu-Awwad (1997) indicated that barley consumptive use was in the range of 187 and 209 mm for the 1993/94 growing season in the same site. Since irrigation water in arid and semi-arid regions is the most limited input factor in crop production process, the optimal level of water applied is of concern. Water use efficiency was defined as the total crop yield per unit consumptive use per unit area (Hillel and Guron, 1973; Braunworth and Mack, 1989). Water use efficiency varied from 0.0 in R treatment to a maximum of 2.42 kg/mm/ha in F2 treatment. Water use efficiency associated with F2 and F3 treatments were not significantly different, but were significantly higher than water use efficiency in F1, S and R treatments. Also, water use efficiency in F1 treatment was significantly higher by 36.3% than water use efficiency in S treatment. Acknowledgements This research was sponsored by a grant from the Jordan Arid Zone Productivity Project (JAZPP). The author is deeply indebted to Dr. Gorden Spoor for reviewing the manuscript.

References Abu-Awwad, A.M., 1997. Water infiltration and redistribution within soils affected by a surface crust. J. Arid Environ. 37, 231±242.

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