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Soil water storage and surface runoff as influenced by irrigation method in arid soils with surface crust
Agricultural Water Management 37 (1998) 189±203
Soil water storage and surface runoff as influenced by irrigation method in arid soils with surface crust M.I. Al-Qinna, A.M. Abu-Awwad* Department of Agricultural Resources and Environment, Faculty of Agriculture, University of Jordan, Amman, Jordan Accepted 4 May 1998
Abstract The effects of irrigation methods, application rates and initial moisture content on soil water storage and surface runoff were studied in soils liable to surface crust formation during 1995±1996 at the University of Jordan Research Station near Al-Muwaqqar village. Four irrigation methods were tested (sprinkler, furrow, basin and trickle) and four application rates (6.2, 14.4, 24.4 and 28.4 mm/h). Two runs were performed (soil initially dry and soil initially wet). Basin irrigation provided the highest application efficiency followed by trickle, sprinkler and furrow irrigation methods. Entrapping water by the basin borders increased soil water storage by allowing more water to infiltrate through the surface crust. Decreasing the application rate from 28.4 to 6.2 mm/h increased soil water storage significantly in all 150 mm layers to a depth of 600 mm. If the soil was already wet, soil moisture storage decreased owing to siltation during the prewetting and formation of a surface crust and low soil water storage capacity. A sedimentary crust formed at the bottom of the furrows in the furrow irrigation treatment, which reduced soil water storage and increased surface runoff significantly owing to the reduction in infiltration. Increasing the application rate from 6.2 to 28.4 mm/h in the furrow surface irrigation treatment increased the runoff discharge 10fold. Even with the lowest application rate the runoff coefficient under sprinkler irrigation was 20.3% indicating high susceptibility of Al-Muwaqqar soils to surface crust formation. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Surface crust; Sprinkler; Trickle; Furrow; Runoff
* Corresponding author. Fax: 96265355577. 0378-3774/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 3 7 7 4 ( 9 8 ) 0 0 0 5 3 - 5
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1. Introduction With increasing water scarcity, management of irrigation water is becoming the most important factor affecting the agricultural production in arid regions (Arnon, 1972). Water shortages arise from low rainfall (rarely exceeding 150 mm per year), and high losses due to evaporation and runoff. Arid regions are characterized by very low crop production, resulting from drought and deteriorating soil properties. Cultivating such areas more successfully depends upon solving irrigation application problems and preventing deterioration of soil properties. Major soil problems include surface crust formation and surface sealing. Surface seals form under the influence of external forces such as mechanical compaction, raindrop impact, slaking and breakdown of soil aggregates during wetting (Moore, 1981). The first step in soil aggregate disintegration by water droplets, whether from rain or sprinkler irrigation, is a reduction in chemical binding (Gimenez et al., 1992; Levy et al., 1986). The rate of seal formation increases with increasing raindrop energy. The higher the kinetic energy, the steeper the drop in infiltration rate (Agassi et al., 1985; Levy et al., 1986; Smith et al., 1990). Initial moisture content at the beginning of a rain storm greatly affects the resistance of surface soil aggregate to breakdown (Le Bissonnais and Singer, 1992). Entrapping water to prevent runoff in crusted areas can be achieved by using basin and/or furrow tillage which increases soil water storage much more than breaking the soil surface crust only (Stroosnijder and Hoogmoed, 1984; Akasheh and Abu-Awwad, 1997). Surface crust is a major cause of infiltration reduction, surface runoff, high erosion and lower water use efficiency (Bradford et al., 1987; Moore, 1981; Taimeh, 1989). Morin et al. (1981) showed that crust formation was the main process responsible for reducing the hydraulic conductivity by several orders of magnitude below that of the remaining soil profile. McIntyre (1958) indicated that the presence of only 0.1 mm thick crust may reduce the infiltration rate from 8000 mm per day to 700 mm per day and decrease the hydraulic conductivity by 2000-fold. The rearrangement of the clay particles to form a ``plate'' of reduced hydraulic conductivity under wetting may reduce the infiltration volumes by 80% (Moore, 1981). The reduction in the infiltration rate will adversely affect water storage efficiency and hence rainfall or irrigation efficiency, with consequent increase in surface runoff and soil erosion (Bradford et al., 1987; Hoogmoed and Stroosnijder, 1984; Remley and Bradford, 1989). At Al-Muwaqqar soils, 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 a depth, where the stored water is protected from
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evaporation. Also, water quality with low salinity or high sodium-to-calcium ratio may aggravate the problem by reducing the rate at which water enters soil surface (Ayers and Westcot, 1985). Abu-Sharar and Salameh (1995) indicated that slacking 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. They also suggested that clay 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. This paper will describe a filed experiment devised to investigate the effects of irrigation methods (sprinkler, trickle, furrow and basin) and application rates on surface runoff and soil water storage. 2. Materials and methods A field experiment was conducted during 1995±1996 at the University of Jordan Research Station in Al-Muwaqqar village. The area is characterized by a weak vegetation cover and aggregate stability, soil surface of high silt content, strong structural surface crust with an average thickness of 2 mm and 0.625 h (hydraulic resistance). Also, a restricting pan layer existed at a depth of 200±300 mm. The soil classification of the area is fine silty, mixed, thermic, Typic Paleorthid (Taimeh, 1989). Some physical and chemical properties of the soil are given in Tables 1 and 2, respectively. The design was randomized complete block design with split split plot, comprising three experimental factors: application rate as the main factor; irrigation method as the submain factor; and initial soil moisture content as the subsubmain factor. Three replications were used. The experiment layout is depicted in Fig. 1. Application rate comprised four treatments: I6.2, II14.4, III24.4 and IV28.4 mm/h. The total depth of water applied in all treatments was 37.8 mm (this value is equivalent to the allowable depletion depth per single irrigation event), thus the duration of application varied inversely with the application rate. The source of water for sprinkler, furrow and basin irrigation methods was the same from small reservoirs behind earth dams constructed across a seasonal water course, while for the trickle system the source of water was tap water. The average pH, EC (electrical conductivity) and SAR (sodium adsorption ratio) Table 1 Some physical soil properties of the experimental site Horizon
Depth (mm)
Clay (%)
Silt (%)
Sand (%)
Textural class
SG
FC (Pv%)
PWP (Pv%)
MWD (mm)
A1 BA Bw 2BK 2BKm Cr
0±150 150±300 300±450 450±600 600±1000 >1000
300 333 410 422 Ð Ð
667 626 538 508 Ð Ð
33 41 52 70 Ð Ð
Silty Silty Silty Silty Ð Ð
118 138 137 134 Ð Ð
26 28 29 28 Ð Ð
15 17 18 17 Ð Ð
035 Ð Ð Ð Ð Ð
loam clay loam clay clay
SG: specific gravity, FC: field capacity, PWP: permanent welting point, MWD: aggregate stability mean weight diameter.
0±150 150±300 300±450 450±600 600±1000 >1000
A1 BA Bw 2BK 2BKm Cr
223 230 270 287 Ð Ð
CO3 (%) 150 150 165 160 Ð Ð
ECe (dS/m) 832 830 855 809 Ð Ð
pH 100 017 005 009 Ð Ð
OM (%) 07 05 08 29 Ð Ð
Na (me. 100 gÿ1) 201 160 096 032 Ð Ð
K (me. 100 gÿ1) 105 103 102 092 Ð Ð
Ca (me. 100 gÿ1)
32 33 33 31 Ð Ð
Mg (me. 100 gÿ1)
225 232 232 157 Ð Ð
Iron oxides (%)
CO3: calcium carbonate percent, OM: organic matter percent, ECe: paste extract electrical conductivity, exchangeable Ca and Mg measured by atomic absorption, and exchangeable Na and K measured by flame photometer.
Depth (mm)
Horizon
Table 2 Some chemical soil properties of the experimental site
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Fig. 1. Experiment layout. T: trickle, S: sprinkler, F: furrow, B: basin. I, II, III and IV represents 6.2, 14.4, 24.2 and 28.4 mm/h application rates, respectively. The subsubmain experimental treatments, ``dry'' and ``wet'' were applied to the same plots.
values of the earth dam water used in the experiment were 7.8, 2.1 and 4.4 dS/m, respectively, while the pH, EC and SAR values for tap water used in trickle irrigation were 7.5, 0.8 and 8.23 dS/m, respectively. Irrigation methods comprise four treatments: 1. Furrow surface irrigation with an open end (F): furrows (trenches) about 200 mm deep, 200 mm wide, and 2 m apart were established at the soil surface in each plot. 2. Basin surface (B): level basin (zero slope) with soil ridges surrounding each plot. These soil ridges were made high enough (about 250 mm) to prevent water overflowing and runoff during irrigation. 3. Sprinkler (S): sets of 2, 4, 6 and 8 sprinklers were used per plot. The sprinklers were 3 5 4 in./20 mm full circle impact 30B Rain Bird sprinklers with a 32 in. nozzle type (20 mm riser size, 12.3 m flow radius, 0.26 lps discharge at 2.5 bars). They were adjusted to provide the designed application rates with high uniformity (Table 3). 4. Trickle (T): three laterals, 2 m apart, were used in each plot. Each lateral contained 12 Controlled Palm emitter type spaced at 0.5 m. The area of each plot in the four irrigation systems was 6 m6 m. Two antecedent soil moisture contents were used: (a) Dry run: in which water was applied for the first time to the experimental plots with a dry soil condition. Table 3 Uniformity parameters for the sprinkler infiltro-meters Application rate (mm/h)
CU (%)
DU (%)
6.2 14.4 24.4 28.4
78.4 88.9 88.7 91.1
70.3 84.9 87.1 84.5
CU: Uniformity coefficient100 (1ÿY/M), where M is the mean depth of water received and Y is the average deviation of water depth received from the mean (M). DU: Distribution uniformityaverage low quarter of water depth received to the average water depth received.
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Fig. 2. Sprinkler sets layout.
(b) Wet run: in which water was applied to the same experimental plots 48 h after the dry run. The sprinklers were installed in sets of 2, 4, 6, or 8 sprinklers per 6 m6 m plot (Fig. 2) in order to achieve the designed application rates of 6.2, 14.4, 24.4 and 28.4 mm/ h, respectively, with high uniformity, while in furrow and basin infiltro-meters, adjusting the valve at the beginning of each treatment was calibrated to give the required application rate. Water inflow rate into the plot was the same as the application rate (28.4, 24.4, 14.4 and 6.2 mm/h), while the inflow rate into each furrow was 13 the plot application rate (9.5, 8.1, 4.8 and 2.1 mm/h). The water pressure in the sprinkler lines was almost the same and monitored by a pressure gauge installed at each section. Both uniformity coefficient (CU) and distribution uniformity (DU) were measured for the different water application rates of sprinkler irrigation using cans distributed within the tested plots (Table 3). For soil moisture measurements, an access tube was installed in the middle of each plot to a depth of 0.6 m. Soil moisture was monitored before and after each irrigation, starting at a depth of 75 mm and going down to a depth of 525 mm. Soil moisture at the soil surface (0±150 mm) was measured using the gravimeteric method. In sprinkler and basin irrigation systems, the soil surface of each plot was leveled, therefore one access tube was installed in the middle of each plot, while in the furrow and trickle treatments, three access tubes 0.5 m apart were installed across the furrow and the lateral. In the sprinkler and furrow irrigation methods, a runoff collection tank (catchment gauge) was installed at the end of each plot. The runoff amount was measured every
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Fig. 3. Runoff collection device.
5 min. The runoff collection device consisted of a triangular-shaped galvanized steel collector (2 m wide), with a cover (Fig. 3). The collector directed runoff to a V-shaped trough (0.5 m long) that conveyed runoff to two storage barrels connected by a metal pipe (total capacity of 0.5 m3 per plot). Storage barrels were installed underground to allow for free runoff collection by gravity. Barrels were covered by plastic sheets to prevent collection of irrigation water from the sprinklers. Since soil moisture measurements were made to a depth of 600 mm only due to the presence of 100±150 mm thick hard
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petrocalcic horizon at this depth of a very low hydraulic gradient. In addition, soil moisture measurements indicated that the third (300±450 mm) and fourth (450±600 mm) soil layers never reach their field capacities, this accounts no net downward movement of water below the depth of 600 mm. Runoff coefficient in trickle irrigation method was estimated as Runoff coefficient
Water applied ÿ Total water stored ÿ evaporation mm : Water applied mm
The lag time (time from the beginning of irrigation until runoff started) was measured for each treatment. The amount of water stored in the soil profile was calculated from the soil moisture readings. The increase in soil moisture in a certain soil layer after an irrigation event represents the depth of water stored: Soil water storage mm Pv2 ÿ Pv1 D=100; where Pv1 is the volumetric water content (%) before water application, Pv2 is the volumetric water content (%) 24 h after irrigation (mm), and D is the soil depth (mm). In the basin irrigation method, soil water storage immediately after irrigation practice was estimated as: SMS0 h mm SMS24 h Ews24 h ; where SMS0 h is the soil moisture storage immediately after irrigation (mm), SMS24 h is the soil moisture storage 24 h after the irrigation event (mm) measured by the neutron probe, and Ews24 h is the evaporation from wet soil surface during 24 h after wetting (mm). Evaporation from the wet soil surface was calculated using Class A pan dry fetch installed on the experimental site as: r tw ; Ews Ep Kp Ks 1 ÿ td where Ews is the evaporation from wet soil surface (mm per day), Ep the pan evaporation (mm per day), Kp the pan coefficient, a function of wind speed, relative humidity and fetch, which was estimated according to Allen and Pruitt (1991) equation being in the range of 0.52±0.7 for this experiment (Table 4), Ks the soil evaporation factor is 1.0 for basin, trickle (complete wetting of the soil surface) and sprinkler irrigation methods, and is 0.25 for furrow method, tw the time in days from wetting (zero on the day of wetting), and td is the time in days required for the soil surface to become dry after a significant wetting. Based on field observations and the discussion presented by Hill et al. (1982) and Wright (1982), td value was estimated at 5.0 for the soil type of Al-Muwaqqar. Oweis and Taimeh (1996) also, estimated the decay time of the evaporation (N) at 2 for AlMuwaqqar soil type. The calculated evaporation from the wet soil surface ranges from 3.2 to 9.0 mm per day. Kp and Ews were estimated daily according to measured daily wind speed, relative humidity and Ep (Table 4). The Ews during the irrigation period was estimated (as a percent from the 24 h evaporation) and added to the total soil water storage for each treatment.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Day
9.1 9.2 9.2 9.2 9.4 9.5 9.8 8.9 10.2 10.2 10.2 9.9 10.3 10.0 9.3 9.9 9.9 9.9 9.9 11.1 10.3 10.9 10.2 10.2 10.2 10.2 10.6 10.8 11.3 12.0 12.0
0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.53 0.52 0.52 0.55 0.52 0.52 0.52 0.52 0.52 0.59 0.58 0.53 0.52 0.52 0.52 0.52 0.52 0.53 0.54 0.55 0.52 0.54
4.7 4.8 4.8 4.8 4.9 4.9 5.1 4.6 5.3 5.4 5.3 5.2 5.7 5.2 4.8 5.2 5.1 5.2 5.8 6.5 5.5 5.7 5.3 5.3 5.3 5.3 5.6 5.8 6.2 6.2 6.5
12.0 11.1 10.9 10.2 9.6 9.3 9.3 9.3 9.3 9.8 9.8 10.3 11.3 11.3 11.3 9.6 10.1 10.9 10.5 10.6 10.6 10.6 10.1 11.0 10.5 11.3 11.3 11.3 11.3 11.3
Epan
Ews
Epan
Kp
June
May
Month
0.59 0.58 0.59 0.58 0.53 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.53 0.54 0.52 0.59 0.60 0.59 0.53 0.56 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52
Kp 7.1 6.4 6.4 5.9 5.1 4.8 4.8 4.8 4.8 5.1 5.1 5.4 5.9 6.0 6.1 5.0 5.9 6.6 6.2 5.6 5.9 5.6 5.3 5.7 5.5 5.9 5.9 5.9 5.9 5.9
Ews 10.1 10.1 10.1 10.3 10.8 10.8 10.8 10.8 9.6 12.1 12.5 12.5 12.5 12.5 12.2 13.3 13.3 13.3 13.3 13.3 13.3 13.0 13.6 12.5 13.6 13.6 13.6 12.8 13.2 13.2 13.3
Epan
July
0.54 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.58 0.58 0.58 0.60 0.59 0.56 0.52 0.50 0.52 0.52 0.53 0.55 0.57 0.58 0.57 0.52 0.52 0.52 0.52 0.52
Kp 5.5 5.3 5.3 5.4 5.6 5.6 5.6 5.6 5.0 6.3 6.5 7.3 7.2 7.2 7.3 7.9 7.5 6.9 6.6 6.9 6.9 6.9 7.5 7.1 7.9 7.8 7.1 6.7 6.9 6.9 6.9
Ews 13.9 13.9 13.9 13.6 13.8 13.8 12.1 12.1 12.1 12.1 12.1 12.9 13.1 13.9 13.9 13.9 13.2 14.1 14.4 15.6 15.0 15.8 15.8 15.8 15.8 14.5 14.5 14.5 14.5 14.5 14.5
Epan
August
0.52 0.52 0.52 0.57 0.54 0.53 0.53 0.52 0.52 0.52 0.52 0.52 0.52 0.56 0.56 0.52 0.52 0.52 0.52 0.57 0.57 0.56 0.53 0.52 0.53 0.54 0.56 0.56 0.54 0.52 0.52
Kp 7.2 7.2 7.2 7.7 7.5 7.3 6.4 6.3 6.3 6.3 6.3 6.7 6.8 7.8 7.8 7.2 6.9 7.3 7.5 9.0 8.5 8.8 8.3 8.2 8.3 7.9 8.1 8.1 7.8 7.6 7.6
Ews 12.5 12.4 12.3 11.9 11.6 11.6 11.6 11.3 11.5 12.3 12.3 12.3 12.3 12.3 12.5 12.6 13.1 13.7 13.7 13.7 13.7 13.5 12.5 11.4 12.3 12.3 12.3 12.3 13.5 12.4
Epan 0.53 0.56 0.59 0.57 0.52 0.52 0.56 0.59 0.57 0.58 0.53 0.53 0.52 0.52 0.52 0.53 0.58 0.56 0.54 0.52 0.52 0.60 0.58 0.52 0.55 0.55 0.55 0.52 0.52 0.54
Kp
September
6.6 6.9 7.3 6.8 6.0 6.0 6.5 6.7 6.6 7.1 6.5 6.5 6.4 6.4 6.5 6.7 7.5 7.6 7.4 7.1 7.2 8.1 7.3 5.9 6.8 6.8 6.7 6.4 7.0 6.7
Ews 11.2 11.4 10.2 10.2 10.2 10.1 9.9 10.1 9.8 8.5 8.5 8.5 8.3 8.3 8.1 7.8 7.4 7.4 7.4 7.2 6.9 6.6 6.2 6.8 6.8 6.8 7.0 7.1 7.3 7.3 7.0
Epan 0.59 0.52 0.52 0.58 0.58 0.7 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.58 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.53 0.54 0.53 0.56 0.52 0.53
Kp
October
6.6 5.9 5.3 5.9 5.9 7.0 5.2 5.3 5.1 4.4 4.4 4.4 4.3 4.8 4.2 4.1 3.9 3.9 3.9 3.7 3.6 3.4 3.2 3.5 3.5 3.6 3.8 3.8 4.1 3.8 3.7
Ews
Table 4 Measured on site class A pan evaporation (Epan) in mm/day, calculated pan coefficient (Kp) and evaporation from soil surface (Ews) in mm/day
7.0 7.0 6.8 6.5
Epan
0.54 0.57 0.57 0.54
Kp
November
3.8 4.0 3.8 3.5
Ews
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3. Results and discussion 3.1. Soil water storage In the four soil layers, soil water storage was significantly higher in basin irrigation method as compared with that in trickle, sprinkler and furrow irrigation methods (Fig. 4). The increase in soil water storage was the highest in basin surface irrigation method and the lowest in sprinkler irrigation method. In all irrigation methods, soil water storage decreased significantly with soil depth. The reduction in soil water storage with depth in sprinkler irrigation was larger than that in the other irrigation methods. Owing to lateral water movement in furrow irrigation, soil water storage increased significantly in the third and fourth soil layers compared with that in sprinkler method (Fig. 4). Decreasing application rate significantly increased soil water storage in all soil layers. Decreasing application rate from 28.4 to 6.2 mm/h significantly increased soil water storage from 4.1, 3.4, 1.5 and 1.1 to 6.7, 5.7, 2.9 and 2.1 mm/150 mm in the first, second,
Fig. 4. Change in soil water content with depth as influenced by irrigation method.
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Table 5 Effect of application rates on soil water storage (average of both dry and wet runs) in each soil layer (mm/ 150 mm) measured immediately after irrigation, in the top 600 mm soil profile Soil layer
Application rate (mm/h) 6.2
14.4
24.4
28.4
4.7c 3.9c 1.8c 1.3c 11.7
4.1d 3.4d 1.5d 1.1d 10.1
Mean soil water storage (mm) L1 (0ÿ150 mm) L2 (150ÿ300 mm) L3 (300ÿ450 mm) L4 (450ÿ600 mm) Total (mm)
6.7a 5.7a 2.9a 2.1a 17.4
5.1b 4.5b 2.3b 1.7b 13.6
Means followed by the same letter in the same row are not significantly different according to least significant difference test at 5% confidence level.
third and fourth soil layers, respectively. Soil water storage associated with the 6.2 mm/h application rate was the highest for all soil layers (Table 5). This increase was attributed to the long opportunity time for water to infiltrate slowly and subsequently less water loss as surface runoff. Fig. 5 shows that increasing the application rate in sprinkler, furrow and trickle irrigation methods decreased soil water storage. While in basin method, the application rate effect was eliminated by the runoff control measure which minimized water loss by keeping water entrapped on the soil surface. In basin irrigation method, application efficiencies (ratio between the amount of water stored in the soil to total amount of water applied) were the highest being 84.9% and 83.1% in the dry and wet initial soil water content, respectively. This is mainly due to the fact that basin irrigation method provides runoff control and minimizes water loss by keeping water trapped on the soil surface, thus allowing water to infiltrate slowly. About 16% (6 mm) of the applied water was evaporated during the 24 h water ponding in basin irrigation method, because evaporation was admitted from a free water surface and was
Fig. 5. Change in soil water content with depth under sprinkler, furrow, basin and trickle irrigation as influenced by application rate.
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Table 6 Effect of irrigation method and application rate on soil moisture storage (average of both dry and wet runs) in mm measured immediately after irrigation, in the top 600 mm soil profile Irrigation method
Sprinkler Furrow Basin Trickle
Treatment Soil moisture storage (mm/m)
Application efficiency (%)
Application rate (mm/h)
Application rate (mm/h)
6.2
14.4
24.4
28.4
6.2
14.4
24.4
28.4
29.2b 25.4c 32.3a 32.0a
23.4d 17.8f 31.8a 26.8c
20.2e 14.7g 31.6a 23.6d
18.2f 11.6h 31.2a 20.9e
77.2 67.2 85.4 84.7
61.9 47.1 84.1 70.9
53.4 38.9 83.6 62.4
48.1 30.7 82.5 55.3
Means followed by the same letter are not significantly different according to least significant difference test at 5% confidence level.
not from a wet soil surface during the hottest months of the year (May and June). With furrow irrigation, the high velocity of water during application induced the transport and deposition of soil particles from furrow ridges, thereby forming a sedimentary crust of more than 20 mm thick at the bottom of the furrow. This sedimentary crust reduced infiltration and water storage more than the surface crust in sprinkler method. Falayi and Bouma (1975) found that the sedimentary crust in furrows had lower porosity than that measured in structural surface crust. They also found that a sedimentary crust of 0.1 mm thick reduced the infiltration rate of a silt loam soil from 8000 to 700 mm per day. The variation of the soil water storage was affected more by the irrigation method than by the application rate (Table 6). Reducing the application rate from 28.4 to 6.2 mm/h increased application efficiency significantly due to less runoff and longer opportunity time for infiltration. The non-significant soil water storage variations in the basin method were only due to variations in the amount of free water on the soil surface available for evaporation, which decreased with decreasing application rates. At the lowest application rate of 6.2 mm/h, soil water storage under trickle irrigation method was not significantly different from basin irrigation. 3.2. Runoff Runoff coefficients as influenced by application rate and irrigation method are presented in Table 7. In all application rates, runoff coefficients were significantly higher in furrow irrigation method as compared with that in sprinkler, trickle and basin methods. Increasing the application rate from 6.2 to 28.4 mm/h significantly increased runoff coefficient from 32% to 67.4% (about two-fold) in furrow irrigation method. This was mainly due to the direct effect of water application on the soil surface condition. Siltation at the bottom of the furrows reduced infiltration and increased surface runoff. Even the lowest application rate of 6.2 mm/h, sprinkler irrigation produced a runoff coefficient of 20.3% on these highly sensitive soils (Al-Muwaqqar soils). The same conclusion was mentioned by Salameh et al. (1991) who found that for soils suffering from surface crust,
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Table 7 Effect of application rate and irrigation method on runoff coefficient (average of both dry and wet runs) Application rate (mm/h)
Irrigation method Sprinkler
Furrow
Basin
Trickle
32.0f 51.8c 59.9b 67.4a
0.0j 0.0j 0.0j 0.0j
10.5I 26.9g 36.4e 43.8d
Runoff coefficient (%) 6.2 14.4 24.4 28.4
20.3h 35.2ef 43.0d 48.3c
Means followed by the same letter are not significantly different according to least significant difference test at 5% confidence level.
a rain intensity of 1±2 mm/h caused runoff, while an intensity of more than 2 mm/h produced floods. Runoff coefficients were significantly higher under sprinkler irrigation compared with trickle irrigation at all application rates owing to the crust created by the action of water droplets. In fact, runoff under trickle irrigation was negligible at 6.2 mm/h application rate and was only observed at high application rates. Runoff coefficient associated with the highest application rate (28.4 mm/h) in trickle irrigation method was 43.8% owing to the decrease in opportunity time for infiltration and the possible reduction in the infiltration rate due to the water quality used in trickle irrigation treatment (Ayers and Westcot, 1985; Abu-Sharar and Salameh, 1995). Results indicated that on these very weakly structured soils, the rapid wetting of the soil, whether it is 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 (Al-Qinna, 1997). Runoff coefficients were strongly affected by application rate, increasing significantly as the application rate increased owing to the decrease in opportunity time for infiltration. The time from the start of irrigation to the start of runoff, or lag time, is a good indication of the direct effect of irrigation method on the soil surface conditions. In all application rates, lag time values in trickle irrigation method were significantly higher than that in sprinkler and furrow irrigation methods. Lag time values associated with the 6.2 mm/h application rate were 212.6, 130.6 and 69.6 min in trickle, sprinkler and furrow irrigation methods, respectively. While, increasing application rate to 28.4 mm/h significantly reduced lag time values to 30.6, 11.2 and 2.5 min for the same respective irrigation methods (Table 8). The high lag time with trickle irrigation was attributed to the fact that water was applied gently with almost zero velocity. With the 28.4, 24.4 and 14.4 mm/h application rates, the lag time was not significantly different under furrow as compared with sprinkler irrigation. Runoff discharge rate also increased with increasing application rate and initial moisture content under sprinkler and furrow irrigation. It was noticeable that irrigation method had a greater effect on runoff than either application rate or initial moisture content. Runoff amount and discharge were higher under furrow irrigation as compared with sprinkler irrigation. Increasing the application rate from 6.2 to 28.4 mm/h increased runoff discharge from 0.1 to 1.0 m3/h.
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Table 8 Effect of application rate and irrigation method on lag time (average of both dry and wet runs) Application rate (mm/h)
Irrigation method Sprinkler
Furrow
Basin
Trickle
69.6c 21.5ef 09.9fg 02.5g
Ð Ð Ð Ð
212.6a 066.7c 043.9d 030.6de
Lag time (min) 6.2 14.4 24.4 28.4
130.6b 037.6de 019.3efg 011.2fg
Means followed by the same letter are not significantly different according to least significant difference test at 5% confidence level.
4. Conclusions Low application rate of irrigation has a positive effect on soil water storage. A rate of 6.2 mm/h increased soil water storage and reduced runoff significantly more than that in the 14.4, 24.4 and 28.4 mm/h application rates. Basin irrigation is considered the most appropriate method for crust-forming soils since it completely prevents surface runoff and is not affected by the application rate. In soils affected by surface crust, increasing the initial soil moisture content increased surface runoff significantly. Low application rates are recommended for all irrigation methods in order to increase soil water storage and to minimize runoff. A wide interval between irrigations is recommended for crusted soils in order to allow the soil surface to dry and to form cracks, so as to improve the initial infiltration in crusted soils. Acknowledgements This research was sponsored by a grant from Jordan Arid Zone Productivity Project (JAZPP). The authors are deeply indebted to Dr. Richard Dunham 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. Abu-Sharar, T.M., Salameh, A.S., 1995. Reduction in hydraulic conductivity and infiltration rate in reduction to aggregate stability and irrigation water turbidity. Agric. Water Manage. 29, 53±62. Agassi, M., Morin, J., Shainberg, I., 1985. Effect of raindrop impact energy and water salinity on infiltration rates of sodic soils. Soil Sci. Soc. Am. J. 49, 186±190. Akasheh, O.Z., Abu-Awwad, A.M., 1997. Irrigation and soil surface management in arid soils with surface crust. J. Arid Environ. 37, 243±250. Allen, G.R., Pruitt, W.O., 1991. FAO-24 reference evapotranspiration factors. J. Irrig. Drain. Eng. 117(5), 758± 773.
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Al-Qinna, I.M., 1997. Infiltration and soil water storage as affected by irrigation method in Al-Muwaqqar region. M.Sc. Thesis, University of Jordan, Amman, Jordan. Arnon, I., 1972. Crop production in arid regions, Learned Hill Books, vol. 1, p. 650. Ayers, R.S., Westcot, D.W., 1985. Water quality for agriculture. Irrig. Drain. Paper no. 29, Rev. 1, FAO Rome, Italy. Bradford, J.M., Ferris, J.E., Remley, P.A., 1987. Interrill soil erosion processes: 1. Effect of surface sealing on infiltration, runoff, and soil splash detachment. Soil Sci. Soc. Am. J. 51, 1566±1571. Falayi, O., Bouma, J., 1975. Relationships between the hydraulic conductance of surface crusts and soil management in a Typic Hapludalf. Soil Sci. Soc. Am. Proc. 39, 957±963. Gimenez, D., Dirksen, C., Miedema, R., Eppink, L.A.A.J., Schoonderbeek, D., 1992. Surface sealing and hydraulic conductances under varying intensity rains. Soil Sci. Soc. Am. J. 56, 234±242. Hill, W.H., Hanks, R.J., Wright, J.L., 1982. Crop yield models adapted to irrigation scheduling programs, Final research report No. 99. Utah Agricultural Experiment Station, Utah State University, Logan, UT. Hoogmoed, W.B., Stroosnijder, L., 1984. Crust formation on sandy soils in the Sahel I. Rainfall and infiltration. Soil and Till. Res. 4, 5±23. Le Bissonnais, Y., Singer, M.J., 1992. Crusting, runoff, and erosion response to soil water content and successive rainfalls. Soil Sci. Soc. Am. J. 56, 1898±1903. Levy, G., Shainberg, I., Morin, J., 1986. Factors affecting the stability of soil crusts in subsequent storms. Soil Sci. Soc. Am. J. 50, 196±201. McIntyre, D.S., 1958. Permeability measurements of soil crusts formed by raindrop impact. Soil Sci. 85, 185± 189. Moore, I.D., 1981. Effect of surface sealing on infiltration. ASAE Trans. 24, 1546±1552. Morin, J., Benyamini, Y., Michaeli, A., 1981. The effect of raindrop impact on the dynamics of soil surface crusting and water movement in the profile. J. Hydrol. 52, 321±335. Oweis, T.Y., Taimeh, A.Y., 1996. Evaluation of a small basin water-harvesting system in the arid region of Jordan. Wat. Res. Manag. 10, 21±34. Remley, P.A., Bradford, J.M., 1989. Relationship of soil crust morphology to interrill erosion parameters. Soil Sci. Soc. Am. J. 53, 1215±1221. Salameh, E., Remawi, O., Bannayan, H., 1991. Groundwater artificial recharge. Water Research and Study Center, University of Jordan. Smith, H.J.C., Levy, G.J., Shainberg, I., 1990. Water droplet energy and soil amendments: Effect on infiltration and erosion. Soil Sci. Soc. Am. J. 54, 1084±1087. Stroosnijder, L., Hoogmoed, W.B., 1984. Crust formation on sandy soils in the Sahel. II. Tillage and its effect on the water balance. Soil and Till. Res. 4, 321±337. Taimeh, A., 1989. Soils of Muwaqqar. University of Jordan. Wright, J.L., 1982. New evaporation crop coefficient. Proc. of Am. Soc. of Civil Engineers. J. Irrig. Drain. Div. 108, 57±74.
Soil water storage and surface runoff as influenced by irrigation method in arid soils with surface crust M.I. Al-Qinna, A.M. Abu-Awwad* Department of Agricultural Resources and Environment, Faculty of Agriculture, University of Jordan, Amman, Jordan Accepted 4 May 1998
Abstract The effects of irrigation methods, application rates and initial moisture content on soil water storage and surface runoff were studied in soils liable to surface crust formation during 1995±1996 at the University of Jordan Research Station near Al-Muwaqqar village. Four irrigation methods were tested (sprinkler, furrow, basin and trickle) and four application rates (6.2, 14.4, 24.4 and 28.4 mm/h). Two runs were performed (soil initially dry and soil initially wet). Basin irrigation provided the highest application efficiency followed by trickle, sprinkler and furrow irrigation methods. Entrapping water by the basin borders increased soil water storage by allowing more water to infiltrate through the surface crust. Decreasing the application rate from 28.4 to 6.2 mm/h increased soil water storage significantly in all 150 mm layers to a depth of 600 mm. If the soil was already wet, soil moisture storage decreased owing to siltation during the prewetting and formation of a surface crust and low soil water storage capacity. A sedimentary crust formed at the bottom of the furrows in the furrow irrigation treatment, which reduced soil water storage and increased surface runoff significantly owing to the reduction in infiltration. Increasing the application rate from 6.2 to 28.4 mm/h in the furrow surface irrigation treatment increased the runoff discharge 10fold. Even with the lowest application rate the runoff coefficient under sprinkler irrigation was 20.3% indicating high susceptibility of Al-Muwaqqar soils to surface crust formation. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Surface crust; Sprinkler; Trickle; Furrow; Runoff
* Corresponding author. Fax: 96265355577. 0378-3774/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 3 7 7 4 ( 9 8 ) 0 0 0 5 3 - 5
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1. Introduction With increasing water scarcity, management of irrigation water is becoming the most important factor affecting the agricultural production in arid regions (Arnon, 1972). Water shortages arise from low rainfall (rarely exceeding 150 mm per year), and high losses due to evaporation and runoff. Arid regions are characterized by very low crop production, resulting from drought and deteriorating soil properties. Cultivating such areas more successfully depends upon solving irrigation application problems and preventing deterioration of soil properties. Major soil problems include surface crust formation and surface sealing. Surface seals form under the influence of external forces such as mechanical compaction, raindrop impact, slaking and breakdown of soil aggregates during wetting (Moore, 1981). The first step in soil aggregate disintegration by water droplets, whether from rain or sprinkler irrigation, is a reduction in chemical binding (Gimenez et al., 1992; Levy et al., 1986). The rate of seal formation increases with increasing raindrop energy. The higher the kinetic energy, the steeper the drop in infiltration rate (Agassi et al., 1985; Levy et al., 1986; Smith et al., 1990). Initial moisture content at the beginning of a rain storm greatly affects the resistance of surface soil aggregate to breakdown (Le Bissonnais and Singer, 1992). Entrapping water to prevent runoff in crusted areas can be achieved by using basin and/or furrow tillage which increases soil water storage much more than breaking the soil surface crust only (Stroosnijder and Hoogmoed, 1984; Akasheh and Abu-Awwad, 1997). Surface crust is a major cause of infiltration reduction, surface runoff, high erosion and lower water use efficiency (Bradford et al., 1987; Moore, 1981; Taimeh, 1989). Morin et al. (1981) showed that crust formation was the main process responsible for reducing the hydraulic conductivity by several orders of magnitude below that of the remaining soil profile. McIntyre (1958) indicated that the presence of only 0.1 mm thick crust may reduce the infiltration rate from 8000 mm per day to 700 mm per day and decrease the hydraulic conductivity by 2000-fold. The rearrangement of the clay particles to form a ``plate'' of reduced hydraulic conductivity under wetting may reduce the infiltration volumes by 80% (Moore, 1981). The reduction in the infiltration rate will adversely affect water storage efficiency and hence rainfall or irrigation efficiency, with consequent increase in surface runoff and soil erosion (Bradford et al., 1987; Hoogmoed and Stroosnijder, 1984; Remley and Bradford, 1989). At Al-Muwaqqar soils, 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 a depth, where the stored water is protected from
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evaporation. Also, water quality with low salinity or high sodium-to-calcium ratio may aggravate the problem by reducing the rate at which water enters soil surface (Ayers and Westcot, 1985). Abu-Sharar and Salameh (1995) indicated that slacking 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. They also suggested that clay 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. This paper will describe a filed experiment devised to investigate the effects of irrigation methods (sprinkler, trickle, furrow and basin) and application rates on surface runoff and soil water storage. 2. Materials and methods A field experiment was conducted during 1995±1996 at the University of Jordan Research Station in Al-Muwaqqar village. The area is characterized by a weak vegetation cover and aggregate stability, soil surface of high silt content, strong structural surface crust with an average thickness of 2 mm and 0.625 h (hydraulic resistance). Also, a restricting pan layer existed at a depth of 200±300 mm. The soil classification of the area is fine silty, mixed, thermic, Typic Paleorthid (Taimeh, 1989). Some physical and chemical properties of the soil are given in Tables 1 and 2, respectively. The design was randomized complete block design with split split plot, comprising three experimental factors: application rate as the main factor; irrigation method as the submain factor; and initial soil moisture content as the subsubmain factor. Three replications were used. The experiment layout is depicted in Fig. 1. Application rate comprised four treatments: I6.2, II14.4, III24.4 and IV28.4 mm/h. The total depth of water applied in all treatments was 37.8 mm (this value is equivalent to the allowable depletion depth per single irrigation event), thus the duration of application varied inversely with the application rate. The source of water for sprinkler, furrow and basin irrigation methods was the same from small reservoirs behind earth dams constructed across a seasonal water course, while for the trickle system the source of water was tap water. The average pH, EC (electrical conductivity) and SAR (sodium adsorption ratio) Table 1 Some physical soil properties of the experimental site Horizon
Depth (mm)
Clay (%)
Silt (%)
Sand (%)
Textural class
SG
FC (Pv%)
PWP (Pv%)
MWD (mm)
A1 BA Bw 2BK 2BKm Cr
0±150 150±300 300±450 450±600 600±1000 >1000
300 333 410 422 Ð Ð
667 626 538 508 Ð Ð
33 41 52 70 Ð Ð
Silty Silty Silty Silty Ð Ð
118 138 137 134 Ð Ð
26 28 29 28 Ð Ð
15 17 18 17 Ð Ð
035 Ð Ð Ð Ð Ð
loam clay loam clay clay
SG: specific gravity, FC: field capacity, PWP: permanent welting point, MWD: aggregate stability mean weight diameter.
0±150 150±300 300±450 450±600 600±1000 >1000
A1 BA Bw 2BK 2BKm Cr
223 230 270 287 Ð Ð
CO3 (%) 150 150 165 160 Ð Ð
ECe (dS/m) 832 830 855 809 Ð Ð
pH 100 017 005 009 Ð Ð
OM (%) 07 05 08 29 Ð Ð
Na (me. 100 gÿ1) 201 160 096 032 Ð Ð
K (me. 100 gÿ1) 105 103 102 092 Ð Ð
Ca (me. 100 gÿ1)
32 33 33 31 Ð Ð
Mg (me. 100 gÿ1)
225 232 232 157 Ð Ð
Iron oxides (%)
CO3: calcium carbonate percent, OM: organic matter percent, ECe: paste extract electrical conductivity, exchangeable Ca and Mg measured by atomic absorption, and exchangeable Na and K measured by flame photometer.
Depth (mm)
Horizon
Table 2 Some chemical soil properties of the experimental site
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Fig. 1. Experiment layout. T: trickle, S: sprinkler, F: furrow, B: basin. I, II, III and IV represents 6.2, 14.4, 24.2 and 28.4 mm/h application rates, respectively. The subsubmain experimental treatments, ``dry'' and ``wet'' were applied to the same plots.
values of the earth dam water used in the experiment were 7.8, 2.1 and 4.4 dS/m, respectively, while the pH, EC and SAR values for tap water used in trickle irrigation were 7.5, 0.8 and 8.23 dS/m, respectively. Irrigation methods comprise four treatments: 1. Furrow surface irrigation with an open end (F): furrows (trenches) about 200 mm deep, 200 mm wide, and 2 m apart were established at the soil surface in each plot. 2. Basin surface (B): level basin (zero slope) with soil ridges surrounding each plot. These soil ridges were made high enough (about 250 mm) to prevent water overflowing and runoff during irrigation. 3. Sprinkler (S): sets of 2, 4, 6 and 8 sprinklers were used per plot. The sprinklers were 3 5 4 in./20 mm full circle impact 30B Rain Bird sprinklers with a 32 in. nozzle type (20 mm riser size, 12.3 m flow radius, 0.26 lps discharge at 2.5 bars). They were adjusted to provide the designed application rates with high uniformity (Table 3). 4. Trickle (T): three laterals, 2 m apart, were used in each plot. Each lateral contained 12 Controlled Palm emitter type spaced at 0.5 m. The area of each plot in the four irrigation systems was 6 m6 m. Two antecedent soil moisture contents were used: (a) Dry run: in which water was applied for the first time to the experimental plots with a dry soil condition. Table 3 Uniformity parameters for the sprinkler infiltro-meters Application rate (mm/h)
CU (%)
DU (%)
6.2 14.4 24.4 28.4
78.4 88.9 88.7 91.1
70.3 84.9 87.1 84.5
CU: Uniformity coefficient100 (1ÿY/M), where M is the mean depth of water received and Y is the average deviation of water depth received from the mean (M). DU: Distribution uniformityaverage low quarter of water depth received to the average water depth received.
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Fig. 2. Sprinkler sets layout.
(b) Wet run: in which water was applied to the same experimental plots 48 h after the dry run. The sprinklers were installed in sets of 2, 4, 6, or 8 sprinklers per 6 m6 m plot (Fig. 2) in order to achieve the designed application rates of 6.2, 14.4, 24.4 and 28.4 mm/ h, respectively, with high uniformity, while in furrow and basin infiltro-meters, adjusting the valve at the beginning of each treatment was calibrated to give the required application rate. Water inflow rate into the plot was the same as the application rate (28.4, 24.4, 14.4 and 6.2 mm/h), while the inflow rate into each furrow was 13 the plot application rate (9.5, 8.1, 4.8 and 2.1 mm/h). The water pressure in the sprinkler lines was almost the same and monitored by a pressure gauge installed at each section. Both uniformity coefficient (CU) and distribution uniformity (DU) were measured for the different water application rates of sprinkler irrigation using cans distributed within the tested plots (Table 3). For soil moisture measurements, an access tube was installed in the middle of each plot to a depth of 0.6 m. Soil moisture was monitored before and after each irrigation, starting at a depth of 75 mm and going down to a depth of 525 mm. Soil moisture at the soil surface (0±150 mm) was measured using the gravimeteric method. In sprinkler and basin irrigation systems, the soil surface of each plot was leveled, therefore one access tube was installed in the middle of each plot, while in the furrow and trickle treatments, three access tubes 0.5 m apart were installed across the furrow and the lateral. In the sprinkler and furrow irrigation methods, a runoff collection tank (catchment gauge) was installed at the end of each plot. The runoff amount was measured every
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Fig. 3. Runoff collection device.
5 min. The runoff collection device consisted of a triangular-shaped galvanized steel collector (2 m wide), with a cover (Fig. 3). The collector directed runoff to a V-shaped trough (0.5 m long) that conveyed runoff to two storage barrels connected by a metal pipe (total capacity of 0.5 m3 per plot). Storage barrels were installed underground to allow for free runoff collection by gravity. Barrels were covered by plastic sheets to prevent collection of irrigation water from the sprinklers. Since soil moisture measurements were made to a depth of 600 mm only due to the presence of 100±150 mm thick hard
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petrocalcic horizon at this depth of a very low hydraulic gradient. In addition, soil moisture measurements indicated that the third (300±450 mm) and fourth (450±600 mm) soil layers never reach their field capacities, this accounts no net downward movement of water below the depth of 600 mm. Runoff coefficient in trickle irrigation method was estimated as Runoff coefficient
Water applied ÿ Total water stored ÿ evaporation mm : Water applied mm
The lag time (time from the beginning of irrigation until runoff started) was measured for each treatment. The amount of water stored in the soil profile was calculated from the soil moisture readings. The increase in soil moisture in a certain soil layer after an irrigation event represents the depth of water stored: Soil water storage mm Pv2 ÿ Pv1 D=100; where Pv1 is the volumetric water content (%) before water application, Pv2 is the volumetric water content (%) 24 h after irrigation (mm), and D is the soil depth (mm). In the basin irrigation method, soil water storage immediately after irrigation practice was estimated as: SMS0 h mm SMS24 h Ews24 h ; where SMS0 h is the soil moisture storage immediately after irrigation (mm), SMS24 h is the soil moisture storage 24 h after the irrigation event (mm) measured by the neutron probe, and Ews24 h is the evaporation from wet soil surface during 24 h after wetting (mm). Evaporation from the wet soil surface was calculated using Class A pan dry fetch installed on the experimental site as: r tw ; Ews Ep Kp Ks 1 ÿ td where Ews is the evaporation from wet soil surface (mm per day), Ep the pan evaporation (mm per day), Kp the pan coefficient, a function of wind speed, relative humidity and fetch, which was estimated according to Allen and Pruitt (1991) equation being in the range of 0.52±0.7 for this experiment (Table 4), Ks the soil evaporation factor is 1.0 for basin, trickle (complete wetting of the soil surface) and sprinkler irrigation methods, and is 0.25 for furrow method, tw the time in days from wetting (zero on the day of wetting), and td is the time in days required for the soil surface to become dry after a significant wetting. Based on field observations and the discussion presented by Hill et al. (1982) and Wright (1982), td value was estimated at 5.0 for the soil type of Al-Muwaqqar. Oweis and Taimeh (1996) also, estimated the decay time of the evaporation (N) at 2 for AlMuwaqqar soil type. The calculated evaporation from the wet soil surface ranges from 3.2 to 9.0 mm per day. Kp and Ews were estimated daily according to measured daily wind speed, relative humidity and Ep (Table 4). The Ews during the irrigation period was estimated (as a percent from the 24 h evaporation) and added to the total soil water storage for each treatment.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Day
9.1 9.2 9.2 9.2 9.4 9.5 9.8 8.9 10.2 10.2 10.2 9.9 10.3 10.0 9.3 9.9 9.9 9.9 9.9 11.1 10.3 10.9 10.2 10.2 10.2 10.2 10.6 10.8 11.3 12.0 12.0
0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.53 0.52 0.52 0.55 0.52 0.52 0.52 0.52 0.52 0.59 0.58 0.53 0.52 0.52 0.52 0.52 0.52 0.53 0.54 0.55 0.52 0.54
4.7 4.8 4.8 4.8 4.9 4.9 5.1 4.6 5.3 5.4 5.3 5.2 5.7 5.2 4.8 5.2 5.1 5.2 5.8 6.5 5.5 5.7 5.3 5.3 5.3 5.3 5.6 5.8 6.2 6.2 6.5
12.0 11.1 10.9 10.2 9.6 9.3 9.3 9.3 9.3 9.8 9.8 10.3 11.3 11.3 11.3 9.6 10.1 10.9 10.5 10.6 10.6 10.6 10.1 11.0 10.5 11.3 11.3 11.3 11.3 11.3
Epan
Ews
Epan
Kp
June
May
Month
0.59 0.58 0.59 0.58 0.53 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.53 0.54 0.52 0.59 0.60 0.59 0.53 0.56 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52
Kp 7.1 6.4 6.4 5.9 5.1 4.8 4.8 4.8 4.8 5.1 5.1 5.4 5.9 6.0 6.1 5.0 5.9 6.6 6.2 5.6 5.9 5.6 5.3 5.7 5.5 5.9 5.9 5.9 5.9 5.9
Ews 10.1 10.1 10.1 10.3 10.8 10.8 10.8 10.8 9.6 12.1 12.5 12.5 12.5 12.5 12.2 13.3 13.3 13.3 13.3 13.3 13.3 13.0 13.6 12.5 13.6 13.6 13.6 12.8 13.2 13.2 13.3
Epan
July
0.54 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.58 0.58 0.58 0.60 0.59 0.56 0.52 0.50 0.52 0.52 0.53 0.55 0.57 0.58 0.57 0.52 0.52 0.52 0.52 0.52
Kp 5.5 5.3 5.3 5.4 5.6 5.6 5.6 5.6 5.0 6.3 6.5 7.3 7.2 7.2 7.3 7.9 7.5 6.9 6.6 6.9 6.9 6.9 7.5 7.1 7.9 7.8 7.1 6.7 6.9 6.9 6.9
Ews 13.9 13.9 13.9 13.6 13.8 13.8 12.1 12.1 12.1 12.1 12.1 12.9 13.1 13.9 13.9 13.9 13.2 14.1 14.4 15.6 15.0 15.8 15.8 15.8 15.8 14.5 14.5 14.5 14.5 14.5 14.5
Epan
August
0.52 0.52 0.52 0.57 0.54 0.53 0.53 0.52 0.52 0.52 0.52 0.52 0.52 0.56 0.56 0.52 0.52 0.52 0.52 0.57 0.57 0.56 0.53 0.52 0.53 0.54 0.56 0.56 0.54 0.52 0.52
Kp 7.2 7.2 7.2 7.7 7.5 7.3 6.4 6.3 6.3 6.3 6.3 6.7 6.8 7.8 7.8 7.2 6.9 7.3 7.5 9.0 8.5 8.8 8.3 8.2 8.3 7.9 8.1 8.1 7.8 7.6 7.6
Ews 12.5 12.4 12.3 11.9 11.6 11.6 11.6 11.3 11.5 12.3 12.3 12.3 12.3 12.3 12.5 12.6 13.1 13.7 13.7 13.7 13.7 13.5 12.5 11.4 12.3 12.3 12.3 12.3 13.5 12.4
Epan 0.53 0.56 0.59 0.57 0.52 0.52 0.56 0.59 0.57 0.58 0.53 0.53 0.52 0.52 0.52 0.53 0.58 0.56 0.54 0.52 0.52 0.60 0.58 0.52 0.55 0.55 0.55 0.52 0.52 0.54
Kp
September
6.6 6.9 7.3 6.8 6.0 6.0 6.5 6.7 6.6 7.1 6.5 6.5 6.4 6.4 6.5 6.7 7.5 7.6 7.4 7.1 7.2 8.1 7.3 5.9 6.8 6.8 6.7 6.4 7.0 6.7
Ews 11.2 11.4 10.2 10.2 10.2 10.1 9.9 10.1 9.8 8.5 8.5 8.5 8.3 8.3 8.1 7.8 7.4 7.4 7.4 7.2 6.9 6.6 6.2 6.8 6.8 6.8 7.0 7.1 7.3 7.3 7.0
Epan 0.59 0.52 0.52 0.58 0.58 0.7 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.58 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.53 0.54 0.53 0.56 0.52 0.53
Kp
October
6.6 5.9 5.3 5.9 5.9 7.0 5.2 5.3 5.1 4.4 4.4 4.4 4.3 4.8 4.2 4.1 3.9 3.9 3.9 3.7 3.6 3.4 3.2 3.5 3.5 3.6 3.8 3.8 4.1 3.8 3.7
Ews
Table 4 Measured on site class A pan evaporation (Epan) in mm/day, calculated pan coefficient (Kp) and evaporation from soil surface (Ews) in mm/day
7.0 7.0 6.8 6.5
Epan
0.54 0.57 0.57 0.54
Kp
November
3.8 4.0 3.8 3.5
Ews
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3. Results and discussion 3.1. Soil water storage In the four soil layers, soil water storage was significantly higher in basin irrigation method as compared with that in trickle, sprinkler and furrow irrigation methods (Fig. 4). The increase in soil water storage was the highest in basin surface irrigation method and the lowest in sprinkler irrigation method. In all irrigation methods, soil water storage decreased significantly with soil depth. The reduction in soil water storage with depth in sprinkler irrigation was larger than that in the other irrigation methods. Owing to lateral water movement in furrow irrigation, soil water storage increased significantly in the third and fourth soil layers compared with that in sprinkler method (Fig. 4). Decreasing application rate significantly increased soil water storage in all soil layers. Decreasing application rate from 28.4 to 6.2 mm/h significantly increased soil water storage from 4.1, 3.4, 1.5 and 1.1 to 6.7, 5.7, 2.9 and 2.1 mm/150 mm in the first, second,
Fig. 4. Change in soil water content with depth as influenced by irrigation method.
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Table 5 Effect of application rates on soil water storage (average of both dry and wet runs) in each soil layer (mm/ 150 mm) measured immediately after irrigation, in the top 600 mm soil profile Soil layer
Application rate (mm/h) 6.2
14.4
24.4
28.4
4.7c 3.9c 1.8c 1.3c 11.7
4.1d 3.4d 1.5d 1.1d 10.1
Mean soil water storage (mm) L1 (0ÿ150 mm) L2 (150ÿ300 mm) L3 (300ÿ450 mm) L4 (450ÿ600 mm) Total (mm)
6.7a 5.7a 2.9a 2.1a 17.4
5.1b 4.5b 2.3b 1.7b 13.6
Means followed by the same letter in the same row are not significantly different according to least significant difference test at 5% confidence level.
third and fourth soil layers, respectively. Soil water storage associated with the 6.2 mm/h application rate was the highest for all soil layers (Table 5). This increase was attributed to the long opportunity time for water to infiltrate slowly and subsequently less water loss as surface runoff. Fig. 5 shows that increasing the application rate in sprinkler, furrow and trickle irrigation methods decreased soil water storage. While in basin method, the application rate effect was eliminated by the runoff control measure which minimized water loss by keeping water entrapped on the soil surface. In basin irrigation method, application efficiencies (ratio between the amount of water stored in the soil to total amount of water applied) were the highest being 84.9% and 83.1% in the dry and wet initial soil water content, respectively. This is mainly due to the fact that basin irrigation method provides runoff control and minimizes water loss by keeping water trapped on the soil surface, thus allowing water to infiltrate slowly. About 16% (6 mm) of the applied water was evaporated during the 24 h water ponding in basin irrigation method, because evaporation was admitted from a free water surface and was
Fig. 5. Change in soil water content with depth under sprinkler, furrow, basin and trickle irrigation as influenced by application rate.
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Table 6 Effect of irrigation method and application rate on soil moisture storage (average of both dry and wet runs) in mm measured immediately after irrigation, in the top 600 mm soil profile Irrigation method
Sprinkler Furrow Basin Trickle
Treatment Soil moisture storage (mm/m)
Application efficiency (%)
Application rate (mm/h)
Application rate (mm/h)
6.2
14.4
24.4
28.4
6.2
14.4
24.4
28.4
29.2b 25.4c 32.3a 32.0a
23.4d 17.8f 31.8a 26.8c
20.2e 14.7g 31.6a 23.6d
18.2f 11.6h 31.2a 20.9e
77.2 67.2 85.4 84.7
61.9 47.1 84.1 70.9
53.4 38.9 83.6 62.4
48.1 30.7 82.5 55.3
Means followed by the same letter are not significantly different according to least significant difference test at 5% confidence level.
not from a wet soil surface during the hottest months of the year (May and June). With furrow irrigation, the high velocity of water during application induced the transport and deposition of soil particles from furrow ridges, thereby forming a sedimentary crust of more than 20 mm thick at the bottom of the furrow. This sedimentary crust reduced infiltration and water storage more than the surface crust in sprinkler method. Falayi and Bouma (1975) found that the sedimentary crust in furrows had lower porosity than that measured in structural surface crust. They also found that a sedimentary crust of 0.1 mm thick reduced the infiltration rate of a silt loam soil from 8000 to 700 mm per day. The variation of the soil water storage was affected more by the irrigation method than by the application rate (Table 6). Reducing the application rate from 28.4 to 6.2 mm/h increased application efficiency significantly due to less runoff and longer opportunity time for infiltration. The non-significant soil water storage variations in the basin method were only due to variations in the amount of free water on the soil surface available for evaporation, which decreased with decreasing application rates. At the lowest application rate of 6.2 mm/h, soil water storage under trickle irrigation method was not significantly different from basin irrigation. 3.2. Runoff Runoff coefficients as influenced by application rate and irrigation method are presented in Table 7. In all application rates, runoff coefficients were significantly higher in furrow irrigation method as compared with that in sprinkler, trickle and basin methods. Increasing the application rate from 6.2 to 28.4 mm/h significantly increased runoff coefficient from 32% to 67.4% (about two-fold) in furrow irrigation method. This was mainly due to the direct effect of water application on the soil surface condition. Siltation at the bottom of the furrows reduced infiltration and increased surface runoff. Even the lowest application rate of 6.2 mm/h, sprinkler irrigation produced a runoff coefficient of 20.3% on these highly sensitive soils (Al-Muwaqqar soils). The same conclusion was mentioned by Salameh et al. (1991) who found that for soils suffering from surface crust,
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Table 7 Effect of application rate and irrigation method on runoff coefficient (average of both dry and wet runs) Application rate (mm/h)
Irrigation method Sprinkler
Furrow
Basin
Trickle
32.0f 51.8c 59.9b 67.4a
0.0j 0.0j 0.0j 0.0j
10.5I 26.9g 36.4e 43.8d
Runoff coefficient (%) 6.2 14.4 24.4 28.4
20.3h 35.2ef 43.0d 48.3c
Means followed by the same letter are not significantly different according to least significant difference test at 5% confidence level.
a rain intensity of 1±2 mm/h caused runoff, while an intensity of more than 2 mm/h produced floods. Runoff coefficients were significantly higher under sprinkler irrigation compared with trickle irrigation at all application rates owing to the crust created by the action of water droplets. In fact, runoff under trickle irrigation was negligible at 6.2 mm/h application rate and was only observed at high application rates. Runoff coefficient associated with the highest application rate (28.4 mm/h) in trickle irrigation method was 43.8% owing to the decrease in opportunity time for infiltration and the possible reduction in the infiltration rate due to the water quality used in trickle irrigation treatment (Ayers and Westcot, 1985; Abu-Sharar and Salameh, 1995). Results indicated that on these very weakly structured soils, the rapid wetting of the soil, whether it is 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 (Al-Qinna, 1997). Runoff coefficients were strongly affected by application rate, increasing significantly as the application rate increased owing to the decrease in opportunity time for infiltration. The time from the start of irrigation to the start of runoff, or lag time, is a good indication of the direct effect of irrigation method on the soil surface conditions. In all application rates, lag time values in trickle irrigation method were significantly higher than that in sprinkler and furrow irrigation methods. Lag time values associated with the 6.2 mm/h application rate were 212.6, 130.6 and 69.6 min in trickle, sprinkler and furrow irrigation methods, respectively. While, increasing application rate to 28.4 mm/h significantly reduced lag time values to 30.6, 11.2 and 2.5 min for the same respective irrigation methods (Table 8). The high lag time with trickle irrigation was attributed to the fact that water was applied gently with almost zero velocity. With the 28.4, 24.4 and 14.4 mm/h application rates, the lag time was not significantly different under furrow as compared with sprinkler irrigation. Runoff discharge rate also increased with increasing application rate and initial moisture content under sprinkler and furrow irrigation. It was noticeable that irrigation method had a greater effect on runoff than either application rate or initial moisture content. Runoff amount and discharge were higher under furrow irrigation as compared with sprinkler irrigation. Increasing the application rate from 6.2 to 28.4 mm/h increased runoff discharge from 0.1 to 1.0 m3/h.
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Table 8 Effect of application rate and irrigation method on lag time (average of both dry and wet runs) Application rate (mm/h)
Irrigation method Sprinkler
Furrow
Basin
Trickle
69.6c 21.5ef 09.9fg 02.5g
Ð Ð Ð Ð
212.6a 066.7c 043.9d 030.6de
Lag time (min) 6.2 14.4 24.4 28.4
130.6b 037.6de 019.3efg 011.2fg
Means followed by the same letter are not significantly different according to least significant difference test at 5% confidence level.
4. Conclusions Low application rate of irrigation has a positive effect on soil water storage. A rate of 6.2 mm/h increased soil water storage and reduced runoff significantly more than that in the 14.4, 24.4 and 28.4 mm/h application rates. Basin irrigation is considered the most appropriate method for crust-forming soils since it completely prevents surface runoff and is not affected by the application rate. In soils affected by surface crust, increasing the initial soil moisture content increased surface runoff significantly. Low application rates are recommended for all irrigation methods in order to increase soil water storage and to minimize runoff. A wide interval between irrigations is recommended for crusted soils in order to allow the soil surface to dry and to form cracks, so as to improve the initial infiltration in crusted soils. Acknowledgements This research was sponsored by a grant from Jordan Arid Zone Productivity Project (JAZPP). The authors are deeply indebted to Dr. Richard Dunham 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. Abu-Sharar, T.M., Salameh, A.S., 1995. Reduction in hydraulic conductivity and infiltration rate in reduction to aggregate stability and irrigation water turbidity. Agric. Water Manage. 29, 53±62. Agassi, M., Morin, J., Shainberg, I., 1985. Effect of raindrop impact energy and water salinity on infiltration rates of sodic soils. Soil Sci. Soc. Am. J. 49, 186±190. Akasheh, O.Z., Abu-Awwad, A.M., 1997. Irrigation and soil surface management in arid soils with surface crust. J. Arid Environ. 37, 243±250. Allen, G.R., Pruitt, W.O., 1991. FAO-24 reference evapotranspiration factors. J. Irrig. Drain. Eng. 117(5), 758± 773.
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