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Influence of different water quantities and qualities on lemon trees and soil salt distribution at the Jordan Valley
Agricultural Water Management 52 (2001) 53±71
In¯uence of different water quantities and qualities on lemon trees and soil salt distribution at the Jordan Valley A.M. Abu-Awwad* Department of Agricultural Resources and Environment, Faculty of Agriculture, University of Jordan, Amman, Jordan Accepted 26 March 2001
Abstract The in¯uences of water quantity and quality on young lemon trees (Eureka) were studied at the University of Jordan Research Station at the Jordan Valley for 5 years (1996±2000). Five water levels and three water qualities were imposed via trickle irrigation system on clay loam soil. The primary effect of excess salinity is that it renders less water available to plants although some is still present in the root zone. Lemon trees water requirements should be modi®ed year by year since planting according to the percentage shaded area, and this will lead into substantial water saving. Both evaporation from class A pan and the percentage shaded area can be used to give a satisfactory estimate of the lemon trees water requirement at the different growth stages. The highest lemon fruit yield was at irrigation water depth equal to evaporation depth from class A pan when corrected for tree canopy percentage area. Increasing irrigation water salinity 3.7 times increased average crop root zone salinity by about 3.8±4.1 times. The high salt concentration at the soil surface is due to high evaporation rate from wetted areas and the nature of soil water distribution associated with drip irrigation system. Then, the salt concentration decreased until the second depth, thereafter, salt concentration followed the bulb shape of the wetted soil volume under trickle irrigation. Irrigation water salinity is very important factor that should be managed with limited (de®cit) irrigation. But increasing amount of applied saline water could result in a negative effect on crop yield and environment such as increasing average crop root zone salinity, nutrient leaching, water logging, increasing the drainage water load of salinity which might pollute ground water and other water sources. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Lemon; Shaded area; Water requirement; Salinity; Jordan
*
Tel.: 962-6-5355000/ext. 2564; fax: 962-6-5355577. E-mail address: [email protected] (A.M. Abu-Awwad). 0378-3774/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 1 2 2 - 6
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1. Introduction Jordan Valley (JV) is located in the Rift Valley, which extends from east Africa to Turkey. It is divided into three parts; North, Middle, and South. The Northern part extends from Tebris Lake to Deir Alla, the Middle JV starts from Deir Alla to the Dead Sea and the Southern JV is extended from Dead Sea to gulf of Aqaba. The climate, soils, and water resources are varied widely among the three parts. The average annual rainfall at the Northern Shuna is about 350, 280 mm at Deir Alla, and 35 mm at Aqaba. Total irrigated land in the JV is about 30,000 ha. Only 23,000 ha currently receive water due to scarce water supply. Water resources in the Kingdom of Jordan are very limited. Irrigation in the JV consumes about 340 million cubic meters. Increasing water demand for domestic use has put a burden on agricultural expansion. The agriculture sector consumes about 75% of the total available water, but its contribution to the gross national income is limited. Due to limitation of water resources in Jordan, marginal quality water has been used for irrigation. For 2010, it is anticipated that marginal water will constitute more than 30% of the available water resources for irrigation. Using such low quality water for irrigation is not possible without adverse impact on the environment and agroecosystem. Soil degradation and pollution of soil, water and agricultural crops are of major concern to the agricultural sector. Therefore, proper management of low quality water is a prerequisite for successful and sustainable farming. The Jordan Valley is the most important irrigated area in Jordan where the lands are used for cultivation of citrus and vegetable production. The Ministry of Agriculture in Jordan (1998) indicated that the total lemon productive area was 1568.6 ha produced 42279 tonnes. About 82.2% of the lemon cropped area concentrated in the JV and produced 90% of Jordan total production. The climatic conditions allow production of out of season agricultural products. Thus, the area is used for exporting vegetables and citrus to Europe and the Gulf countries in winter. Crop production in the arid and semi-arid region is dependent on irrigated agriculture. Under these conditions the farmers are obliged to use irrigation water with high quantities of dissolved salts, invariably accompanied by yield reductions of most crops. Extensive areas of irrigated land have been and are increasingly becoming degraded by salinization and water logging resulting from over irrigation and other forms of poor agricultural management (Ghassemi et al., 1995). The best estimate of the effective salinity when salt is non-uniformly distributed with depth is the mean salinity within the root zone. Crop water production functions relating yield to evapotranspiration are not influenced by water salinity (Shalhevet, 1994). Soils are considered saline if they contain soluble salts in quantities sufficient to interfere with the growth of most crop species. This, however, is not a fixed amount of salt but depends on plant species, the soil texture and water capacity of the soil, and the composition of the salts. According to the definition of US Salinity Laboratory, the saturation extract of a saline soil has an electrical conductivity (ECe) greater than 4 dS/m and an exchangeable sodium percentage (ESP) of less than 15. Plant species differ greatly in their growth response to salinity (Marschner, 1997). Grapefruit and orange threshold ECe values were about 1.7±1.8 dS/m and the rate of yield reduction was about 16% per dS/m. These data were obtained under steady-state
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conditions with available crop varieties. The conditions were uniform salt distribution with depth, small changes with time, unrestricted water supply (heavy leaching), and flood irrigation. Initially the crops were established with non-saline water (Mass, 1986). In practice, under realistic field conditions, uniformity is the exception rather than the rule. Furthermore, crops may have different sensitivities at different stages of growth. In saline substrates Na and Cl are usually the dominant ions. Despite the essentiality of chloride as a micronutrient for all higher plants and of Na as mineral nutrient for many halophytes, the concentrations of both ions in saline substrates by far exceed this demand and lead to toxicity in non-salt-tolerant plants. In many herbaceous crop species, e.g. grapevine and many fruit trees, growth inhibition and injury of the foliage occur even at low levels of NaCl salinization. Under such conditions, water deficit is not a constraint and at least for citrus species, high chloride sensitivity and thus toxicity is the major constraint (Mass, 1993). Green and Moreshet (1979), using weighing lysimeters to measure daily ET concluded that the crop factor I/Ep (I and Ep are irrigation water and pan evaporation in millimeter, respectively), when corrected for atmospheric resistance variations represents real tree conductance and can be used for irrigation scheduling. Chartzoulakis et al. (1999) indicated that orange (Bonanza) canopy diameter, plant height and trunk diameter were not significantly different in 0.01 and 0.05 MPa soil water potentials treatments, but were significantly reduced at 1.5 MPa soil water potential. Lemon tree is a salt-sensitive crop to salinity (Cerda et al., 1990; Mass and Hoffman, 1977) and even low salt concentrations may affect its growth and productivity (Shalhevet et al., 1974; Cole and McLeod, 1985; Levy and Shalhevet, 1990). Nastou et al. (1999) indicated that higher salinity in the rooting medium significantly reduced the shoot length. However, the extent of this reduction was different for each cultivar. The yield of mature grapefruit trees was reduced by 13.5% as electrical conductivity of the soil saturation extract increased 1.0 dS/m above a threshold value of 1.2 dS/m (Bielorai et al., 1978). Also, they indicated that total water uptake was reduced as salt concentration in the soil increased. A considerable amount of data is available regarding the effect of irrigation water and soil salinity on crop yield. But, most of the data was obtained with crop established prior to the introduction of saline conditions. In addition, crops may have different sensitivities at different stages of growth and the duration of exposure (Shalhevet, 1994). However, available data for citrus trees in general are limited and almost negligible for lemon. Therefore, a field experiment was conducted to investigate the influence of different water and salinity levels on the development of young lemon (Eureka) trees (since planting), under the Jordan Valley conditions. 2. Materials and methods A field experiment was conducted for 5 years from 1996 to 2000 at the Experimental Research Station of the University of Jordan in the Jordan Valley on lemon (Citrus Limon [L.] Burm. F.) Eureka. The site represents areas of Jordan characterized by low rainfall falling in the winter season (November to April). The climates of the area being characterized by hot summer and warm winter. The annual rainfall ranges between 40 and
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Table 1 Some physical and chemical properties of the soil at the experiment sitea Soil depth (cm)
Clay (%)
Silt (%)
Sand (%)
Texture class
SG
FC (Pv%)
PWP (Pv%)
ECe (dS/m)
0±20 20±40 40±60 60±80
31.8 38.4 35.0 35.2
30.9 22.6 29.3 26.1
37.3 39.0 35.7 38.7
Clay Clay Clay Clay
1.47 1.52 1.49 1.57
27.4 28.5 29.1 27.0
10.5 10.2 11.3 11.2
1.1 1.1 1.1 1.1
loam loam loam loam
0.021b 0.021 0.021 0.021
a SG: specific gravity, FC: field capacity, PWP: permanent wilting point, ECe: paste extract electrical conductivity. b 0.021 is the standard deviation.
274 mm, with an average rainfall of 154 mm during the period of 1996±2000. January is the coolest month of the year, while August is the warmest month. Some physical and chemical properties of the experiment site soil are presented in Table 1. Field capacity (280 mm/m) and permanent wilting point (108 mm/m) were estimated in the laboratory for each soil depth on undisturbed soil samples using the ceramic plate apparatus at 0.3 and 15 bars, respectively. Field capacity for the first soil layer was also determined and checked in the field. One-year-old lemon seedlings were planted on the 15 March 1996 at a spacing of 5 m 5 m. The experimental design was factorial completely randomized block, with three replications. The soil was clay loam (35.1 and 27.2% clay and silt, respectively) with good natural drainage. Drip irrigation was used with one dripper per tree for the first year, two drippers 1.0 m apart per tree for the second year and thereafter four drippers 1.0 m apart (zigzag lateral for each tree) were used per tree. The drippers were Controlled Palm emitter types of 8 lph. The experiment consisted of five water levels and three water qualities. The average daily rate of transpiration under trickle irrigation is a function of conventionally computed average rate of daily consumptive use and the extent of the plant canopy (shaded area). A relatively simple relation (Keller and Bliesner, 1990) that serves for this estimate is Pd Pd Td Ud 0:15 1:0 (1) 100 100 where Td is the average transpiration rate for a crop under trickle irrigation, Ud the conventionally computed average daily consumptive use rate (in this study the average daily class A pan evaporation (Ep) is used), and Pd is the ground area within the drip line shaded by the crop canopies at midday as a percentage of the total ®eld area (%). The ®ve water levels: W0 0:0, W1 0:25, W2 0:5, W3 0:75, W4 1:0 and W5 1:5 times W4 (W4 T d as calculated by Eq. (1)). The three water qualities: S1 irrigation water from King Abdulah canal with an average salinity of 1.33 dS/m, S2 mixed irrigation water from irrigation water and drainage water with an average salinity of 3.10 dS/m, and S3 drainage water with an average salinity of 4.88 dS/m. The shaded area was only measured in W4S1 treatment to quantify irrigation water requirements for the expected reference trees with fresh irrigation water. Pd was measured by marking off the area allocated to a tree (5 m 5 m) in the field and
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measuring the shaded area using a 0.2 m grid system on monthly basis at midday. Irrigation was practiced weekly (May to November). For each irrigation level, three access tubes were installed around one tree at 0.5, 1.0 and 1.5 m from the tree trunk to a depth of 1.0 m. Soil moisture was measured weekly just before the irrigation event using field calibrated neutron probe at depth increments of 0.20 m from a depth of 0.10 m to a depth of 0.90 m. Soil moisture at the surface layer (0± 0.20 m) was determined using the gravimetric method. Class A pan evaporation measured on site, for the period between two irrigation events was used to quantify the required amount of irrigation water to be added for each treatment. The experiment was started with the soil water content near field capacity. Soil water depletion (crop evapotranspiration, Etc) for the period between irrigation was estimated from the soil water content measurements. During short periods when field capacity was reached and/or exceeded due to water applied, drainage water was estimated from dEtc d2
d1
d2 d1 dw ; where d2 dFC dD 0:0 if d2 > dFC ; then d2 dFC and dD d w
dFC
d1 dw
dEtc
where dEtc is the measured soil water depletion depth, d1 and d2 the equivalent depths of moisture in the root zone just before and after irrigation, respectively, dD the drainage water depth, and dw the water (irrigation plus precipitation) depth applied. Lemon tree stem diameter and shaded area were measured monthly. Irrigation water salinity was measured weekly directly after each irrigation event. Lemon fruits (yield) were harvested and weighed at the ripen time. The soil profile at three locations (0.5, 1.0 and 1.5 m from the tree trunk) was divided into four soil layers (0±0.2, 0.2±0.4, 0.4±0.6, and 0.6±0.8 m). Representative soil samples were collected from each grid, and composite samples of the 12 grids for each profile were prepared. The electrical conductivity of the soil saturation paste extract (ECe) was determined. 3. Results and discussions 3.1. Irrigation water quantity and quality The amount of rainfall, evaporation and applied irrigation water are presented in Table 2. Ayers and Westcot (1985), classified water qualities according to their effects on crop water availability into <0.7, 0.7±3.0 and >3.0 dS/m as none, slight to moderate and severe, respectively. For each irrigation water salinity treatment used in this study, variations in irrigation water salinity were not significant and almost constant for the last 5 years. Fresh irrigation water (S1) treatment salinity varies from 1.21 to 1.46 with an average of 1:33 0:059 dS/m (slight to moderate restriction on use). While, irrigation water salinity in S2 and S3 treatments varies from 2.80 to 3.34 with an average 3:10 0:159 dS/m (moderate to severe restriction on use) and from 4.33 to 5.33 with an
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Table 2 Amounts of applied irrigation water to lemon trees for each water level, for the 5 years (1996±2000) Rainfall R (mm) a
274
Ep (mm)
1444
Water levels
1996±1997 I
W0 W1 W2 W3 W4 W5
b
0 58 115 173 230 345
Kp
c
0.00 0.04 0.08 0.12 0.16 0.20
167
40
133
1991
1875
1653
1575
1997±1998
1998±1999
1999±2000
2000
I
Kp
I
Kp
I
Kp
I
Kp
0 88 175 263 351 526
0.00 0.04 0.09 0.13 0.18 0.27
0 91 181 272 363 544
0.00 0.05 0.10 0.15 0.19 0.29
0 117 235 352 470 704
0.00 0.07 0.14 0.21 0.28 0.43
0 123 246 370 493 739
0.00 0.08 0.16 0.23 0.31 0.47
a
Ep represents class A evaporation only during the irrigation period. I: irrigation water applied (mm). c Kp is the crop factor (I/Ep). b
average of 4:88 0:319 dS/m (severe restriction on use), respectively. Chemical analysis for both fresh (S1) and saline (S3) irrigation water qualities on 17 May 2000 was as follows: Parameter
Fresh irrigation water (S1)
Saline irrigation water (S3)
Specific conductance (dS/m) Laboratory pH (units) Calcium by titration (mg/l) Magnesium by calculation (mg/l) Sodium by flame photometry (mg/l) Potassium by flame photometry (mg/l) Chloride by titration (mg/l) Sulfate (mg/l) CO3 by titration (mg/l) Bicarbonate, H2SO4 by titration (mg/l) Nitrate by spectrophotometer (mg/l) Sodium adsorption ratio (SAR)
1.16 7.73 58.9 30.9 123.5 16.0 194.8 93.1 0.0 216.9 20.0 3.23
4.86 7.95 178.0 156.4 699.0 72.1 1206.9 836.9 0.0 153.5 55.8 9.2
3.2. Soil salt distribution With irrigation water salinity of 1.33 dS/m (S1) the average soil profile salinity (ECe) is relatively low and less than 2 dS/m for the three irrigation water levels (W3, W4 and W5). Soil salinity classified as non-saline in which salinity effects are negligible, according to guidelines for soil salinity classes and crop growth (Ayers and Westcot,
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Table 3 Soil salt distribution (ECe in dS/m) as influenced by S1 irrigation water salinity at W3 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
1.6 1.2 1.1 1.0
1.6 2.7 1.7 1.0
1.4 1.2 1.2 1.0
1.53 1.70 1.33 1.0
1.23
1.75
1.20
1.39
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
1985). The average ECe along the soil profile at the same three irrigation water treatments indicates that salt concentration still below the steady-state (ECe 1:5ECiw), might be due to the positive effect of winter rainfall (481 mm). Tables 3±5 show the soil salt distribution and concentration along the soil profile at W3, W4 and W5 irrigation water treatments, respectively, using S1 irrigation water salinity. The general salt profile at the three water treatments followed the typical Table 4 Soil salt distribution (ECe in dS/m) as influenced by S1 irrigation water salinity at W4 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
1.3 1.4 1.1 1.1
2.4 1.8 4.5 1.6
1.2 1.1 1.5 0.9
1.63 1.43 2.37 1.2
1.23
1.58
1.18
1.66
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
Table 5 Soil salt distribution (ECe in dS/m) as influenced by S1 irrigation water salinity at W5 water levels (2000)a Distance from tree trunk (m)
Average a
Average
0.5
1.0
1.5
1.4 1.3 1.4 1.1
2.1 2.4 5.3 1.9
1.3 1.0 1.4 1.2
1.60 1.57 2.7 1.4
1.3
2.93
1.23
1.82
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
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A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
steady-state salt distribution under trickle irrigation (bulb shape) with maximum ECe was at 1.0 m from the tree trunk. Salts accumulated at the soil surface were due to the nature of trickle irrigation method and wet soil surface evaporation. At the soil surface, salt concentration increased from 1:1 0:021 dS/m (initial soil salt concentration, March 1996) to an average of 1.53, 1.63 and 1.6 dS/m at W3, W4 and W5 treatments (March 2000), respectively. At W3 treatment the highest salt concentration being 2.7 dS/m at a distance of about 1.0 m from the tree trunk at the second soil layer (0.2±0.4 m), might be due to the limited amount of applied irrigation water (Table 2). While, soil salts concentration were the highest (4.5 and 5.3 dS/m) at the third soil layer (0.4±0.6 m) of the same distance from tree trunk in W4 and W5 treatments, respectively. Amounts of applied irrigation water in these treatments were high enough to cause some leaching to a deeper soil layer. The low salt concentration at the fourth soil layer (0.6±0.8 m) is due to the nature of the bulb wetting under trickle irrigation system. At S3 treatment soil salt distribution followed the same trend as in S1 treatment at the different water levels. Irrigation water salinity in S3 treatment was almost 3.7 times higher than irrigation water salinity in S1 treatment, and consequently increased average root zone salinity by about 3.8, 4.1 and 4.1 times at W3, W4 and W5 treatments, respectively (Tables 6±8). The average root zone salinity at S3 treatment was 5.32, 6.84 and 7.55 dS/m in W3, W4 and W5 treatments, respectively. Soil salinity classified as moderately saline where yields of Table 6 Soil salt distribution (ECe in dS/m) as influenced by S3 irrigation water salinity at W3 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
4.8 4.3 4.9 2.6
8.4 9.0 6.8 3.6
8.1 4.1 4.2 3.0
7.1 5.8 5.3 3.1
4.15
6.95
4.85
5.32
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
Table 7 Soil salt distribution (ECe in dS/m) as influenced by S3 irrigation water salinity at W4 water levels (2000)a Distance from tree trunk (m)
Average a
Average
0.5
1.0
1.5
4.3 5.2 4.8 3.5
10.2 6.1 14.8 6.0
6.4 5.9 8.4 6.5
6.97 5.73 9.33 5.33
6.8
6.84
4.45
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
9.28
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Table 8 Soil salt distribution (ECe in dS/m) as influenced by S3 irrigation water salinity at W5 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
5.5 5.7 5.2 6.3
12.6 7.2 11.9 8.2
8.0 6.7 7.1 6.2
8.7 6.53 8.07 6.9
4.85
7.55
4.15
6.95
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
many crops are restricted (Ayers and Westcot, 1985). Except at the soil surface the highest salt concentration was at 0.2±0.4 (9.0 dS/m), 0.4±0.6 (14.8 dS/m) and 0.4±0.6 m (11.9 dS/m) soil layer in W3, W4, and W5 treatments, respectively, with S3 treatment at 1.0 m distance from the tree trunk. The average root zone salt concentration was less than expected salt concentration at steady-state in W3 and W4 treatments, however, it reached the expected steady-state salt concentration at W5 treatment due to continues excess irrigation. The same soil salt distribution pattern was noticed at the third distance (1.5 m from the tree trunk) as at 1.0 m distance, but with lower salt concentrations. The high salt concentration being at the soil surface is due to high evaporation rate from the wetted area, then salt concentration decreased until the second depth, thereafter, salt concentration followed the bulb shape of the wetted soil volume under trickle irrigation. At the 0.5 m distance from the tree trunk, soil salt concentration (ECe) significantly decreased and was almost uniform at all depths. The low salt concentration was due to the excessive amount of irrigation water applied close to the trickle point source causing leaching of salts. 3.3. Water uptake Table 9 illustrates the seasonal water balance components for the 1999 and 2000 growing seasons. For both 1999 and 2000 growing seasons, the highest water use was in W5S1 treatment being 546 and 606 mm/year, followed by 517 and 591 mm/year, respectively, in W4S1 treatment. During 1999 increasing irrigation water salinity from 1.33 to 3.1 and 4.88 dS/m reduced annual water use by about 8 and 10%, respectively, in W4 treatment, and by 18 and 14%, respectively, in W5 treatment. The effects of irrigation water salinity were even more pronounced in the fifth year (2000), when lemon annual water use reduced by about 18 and 25% as irrigation water salinity increased from 1.33 to 3.1 and 4.88 dS/m, respectively, at W4 and W5 treatments. Thus, the primary effect of excess salinity is that it renders less water available to plants although some is still present in the root zone. This is because the osmotic potential of soil solution increases as the salt concentration increases (Abu-Awwad and Hill, 1990; Ayers and Westcot, 1985).
62
Treatment
S1 W1
Desired irrigation (fraction of Td) 1999 Irrigation depth (mm) Rainfall depth 40 (mm) Drainage depth (mm) Annual change in soil moisture (mm) Annual water use (Etc)b (mm) 2000 Irrigation depth (mm) Rainfall depth 133 (mm) Drainage depth (mm) Annual change in soil moisture (mm) Annual water use (Etc)b (mm) a b
0.25
S2 W2 0.5
W3 0.75
W4 1.0
W5 1.5
W1 0.25
S3 W2 0.5
W3 0.75
W4 1.0
W5 1.5
W1
W2
0.25
0.5
W3 0.75
W4 1.0
W5 1.5
0a
235
352
470
704
0a
235
352
470
704
0a
0a
352
470
704
± ± ±
2 1 274
5 3 390
11 18 517
160 38 546
± ± ±
0 12 263
0 17 375
2 31 477
244 55 445
± ± ±
± ± ±
0 24 368
0 43 467
250 57 471
0a
246
370
493
739
0a
246
370
493
739
0a
0a
370
493
739
± ± ±
0 14 365
13 18 472
15 20 591
220 46 606
± ± ±
25 11 343
67 16 420
82 41 503
290 68 514
± ± ±
± ± ±
68 31 404
105 46 475
294 95 483
No irrigation water was applied (there were no trees). Estimated from soil water content measurements.
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Table 9 Estimated seasonal water balance components for the years of 1999 and 2000
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With deficit irrigation, increasing irrigation water increased available water for transpiration and evaporation. The increase in transpiration was dominant with the limited available water (W0 to W4), while evaporation and drainage were dominant in the higher water level treatment (W5). In S1 and S2 treatments, the percentage increase in annual water use was in proportion with percentage increase in irrigation water applied as irrigation water level increased from W1 to W4. Increasing irrigation water will increase water use up to the potential Etc, after which increasing irrigation water will not significantly affect Etc. Doorenbos and Kassam (1979) reported that crop water requirement for mature citrus is in the range of 900±1200 mm/growing periods. Results indicate that water requirement for lemon trees, even at the fifth year from planting, is still about half the quantity suggested by Doorenbos and Kassam (1979). 3.4. Shaded area Fig. 1 illustrates the change in the mean monthly Pd with time for lemon trees. In the first year (1996), there was no significant increases in the mean monthly Pd. While during 1997 there was a significant increase in the Pd, before pruning. Pruning was done for the first time in August of the second year (1997). In the third year (1998), shaded areas significantly increased during the year with maximum Pd in October. In the fourth year (1999), shaded area was about 3, 5 and 15 times significantly higher than in the years of 1998, 1997 and 1996, respectively. There was no significant change with time in shaded area during 1999. This might be due to the flowering that was started during the third year and harvesting of lemon fruits was carried out late the same year. Also, annual rainfall was very low being 40 mm during the winter season of 1999 compared to 274 and 167 mm annual rainfall of 1997 and 1998 winter seasons, respectively (Table 2). On the fifth year (2000), lemon trees shaded area significantly increased as compared with the past 4 years (1996±1999). The significant increase in the shaded area started early on the month of July, and significantly increased with time along the growing season. The highest shaded area being 23.7% during the month of September 2000. The average percentage shaded area significantly increased with time being 1.11, 2.89, 5.17, 15.8 and 22.34% in the first, second, third, fourth and the fifth years, respectively. Consequently, the average amount of irrigation water applied increased each year in all treatments, as plants were growing (Table 2). In W4 treatment, the crop factor I/Ep was about 0.16 increasing to 0.18 and to 0.19 for the second and third years, respectively. In the fourth and fifth years, the crop factor increased to 0.28 and 0.31, respectively (about 1.5±1.6 times that in the third year). This indicates that the first 3 years were devoted for adaptation and root development, and the significant vegetative growth started with the fourth year and consequently water requirement. Applied irrigation water increased by 53, 58, 104 and 114% in the second, third, fourth and fifth years, respectively, as compared to amount of applied during the first year. Without supplemental irrigation, lemon trees cannot survive the first year with a total rainfall of 274 mm. In W1 treatment, supplementing winter rainfall with 25% of Td evaporation during the summer months (May to October) using S1 and S2 water qualities succeed to maintain lemon trees alive for the first 3 years (1996 to 1998) and only for the first 2 years (1996±1997) using S3 water quality. Due to poor water quality (high salinity) in S3 treatment, supplementing
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Fig. 1. Mean monthly lemon trees shaded area (%) for treatment W4S1.
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winter rainfall with 50% of Td hardly succeeded to maintain lemon trees alive for the first 3 years, but not with S1 and S2 water quality treatments. Owing to the dry winter (40 mm) of 1998/1999 winter season, most of the stressed lemon trees died in the third year. Thus, evaporation from class A pan when corrected for tree canopy percentage shaded area can represent a good estimate of lemon trees water requirement. 3.5. Stem diameter Table 10 illustrates the influence of different water quantities and qualities on lemon tree stem diameter. During 1996, stem diameter varies from a minimum of 12 mm in W1 with S3 treatment to a maximum of 17 mm in W4 with S2 treatment. With deficit irrigation, increasing amount of applied irrigation water partially compensated for the adverse effect of irrigation water salinity, and consequently increased lemon tree stem diameter. In S1 irrigation water quality, although amount of applied irrigation water increased from W2 to W5 stem diameter was almost the same for the first 4 years (1996± 1999), but was significantly higher than that in W1 water treatment. However, in the fifth year (2000), stem diameter starts to increase more in the higher water level treatments, Table 10 Stem diameter as influenced by irrigation water quantity and qualitya Water levels W1
W2
W3
W4
W5
1996 S1 S2 S3
13.3 bcd 13.7 bcd 12.0 d
16.3 ab 16.0 ab 12.3 cd
15.3 abc 16.0 ab 13.7 bcd
16.0 ab 17.0 a 15.0 abcd
14.3 abcd 16.3 ab 14.7 abcd
1997 S1 S2 S3
11.7 cd 25.0 abc 6.3 d
30.3 ab 25.7 abc 5.7 d
36.0 a 29.3 ab 16.7 bcd
33.0 ab 36.0 a 28.7 ab
32.3 ab 33.0 ab 26.3 abc
1998 S1 S2 S3
14.0 de 10.3 de 0e
51.0 ab 37.3 bc 7.3 de
56.3 ab 44.0 abc 22.3 cd
63.0 a 55.7 ab 44.7 ab
53.0 ab 50.3 ab 39.0 bc
1999 S1 S2 S3
0e 0e 0e
71.3 abc 52.7 cd 0e
77.3 ab 58.3 bcd 16.0 e
82.7 a 71.7 abc 64.3 abcd
81.0 a 73.3 abc 47.7 d
2000 S1 S2 S3
0e 0e 0e
76.0 abcd 58.7 cd 0e
86.3 ab 62.7 bcd 16.7 e
87.3 a 76.7 abcd 70.3 abcd
90.0 a 80.7 abc 55 d
a
For each year, values with the same letter are not significantly different at 5% probability level using Duncan's multiple range test.
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but not significantly. Almost the same trend was in S2 irrigation water salinity. With S3 irrigation water salinity, the significantly highest stem diameter was in W4 water level treatment and was reduced not significantly in W5 treatment. In the fifth growing season (2000), stem diameter was the highest in W5 treatment at S1 (90 mm) and S2 (80.7 mm) treatments but was not significantly higher than that in W2, W3 and W4 water levels. However, in S3 water quality treatment stem diameter (70.3 mm) was the highest in W4 water level treatment, but was not significantly higher than stem diameter (55 mm) in W5 water level treatment. In general, the significant increase in stem diameter was in the first 2 years (3±4 times stem diameter at planting) and continued to increase but in a decreasing increment for the following years. 3.6. Lemon yield Lemon fruits were harvested for the first time on the month of November 1999, about 44 months from planting date. The influence of irrigation water quantities and qualities on fruit yield of the year 1999 is illustrated in Fig. 2. Regardless of irrigation water salinity, lemon production was a complete failure in W0 and W1 treatments. Increasing amount of applied irrigation water in W2 treatment to double the amount applied in W1 treatment gave 16.7, 5.3, and 0.0 kg per tree of lemon fruit yield in S1, S2 and S3 treatments, respectively. In S1 treatment, increasing irrigation water level from W2 to W3, W4 and W5 treatments did not affect lemon fruit yield, with a slight non-significant decrease at W5. However, in S2 and S3 treatments, increasing amount of applied irrigation water substantially but non-significantly increased lemon fruit yield. With S2 irrigation water salinity lemon fruit yield increased from 0.0 to 5.3, 8.9, 13.9, and 10.3 kg per tree as irrigation water level increased from W1 to W2, W3, W4, and W5 treatments, respectively. The same trend was in S3 treatment (Fig. 2), but there was no yield in W2 treatment and yield non-significantly increased to 2.8, 4.5 and 1.6 kg per tree as irrigation water level increased from W2 to W3, W4 and W5 treatments, respectively. In general, with the same irrigation water salinity the highest yield was obtained in W4 treatment being 17.0, 13.9, and 4.5 kg per tree in S1, S2, S3 treatments, respectively. In S1 treatment at all water levels but W1, lemon fruit yield was significantly higher than that in S3 treatment (Fig. 2). Lemon fruit yield in S1 treatment was consistently but not significantly higher than that in S2 treatment at all water levels but in W2. During 2000 growing season, lemon fruits were harvested two times (August and November). Fruit yield as influenced by irrigation water quantity and quality is illustrated in Fig. 3. The significantly highest yield (32.9 kg per tree) was in W4S1 treatment. Increasing irrigation water level from W1 to W2, W3 and W4 treatments significantly increased (almost linearly) fruit yield in all salinity treatments. However, lemon fruit significantly reduced as irrigation water level increases from W4 to W5 treatment at all salinity treatments. Crop production functions that describes the response of lemon fruit yield to amount of irrigation water applied as a percent of Td (Eq. (1)) were developed at the three salinity treatments (2000), and regression analysis gave the following relationships: LFY
21:55 95:21W
42:77W 2 ;
r 2 0:97 at S1 treatment
(2)
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
Fig. 2. Influence of irrigation water quantities and qualities on Lemon yield (1999).
67
68 A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
Fig. 3. Influence of irrigation water quantities and qualities on Lemon yield (2000).
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
LFY LFY
11:39 46:24W 22:67 55:83W
18:44W 2 ; 2
24:27W ;
69
r 2 0:89 at S2 treatment 2
r 0:79 at S3 treatment
(3) (4)
where LFY is the lemon fruit yield in kilogram per tree and W is the percentage of Td (i.e. 0.25, 0.5, 0.75, etc.). Increasing the amount of applied irrigation water more than that applied in W4 treatment might leached salts to a deeper soil layer but also leached plant nutrients, which may affected crop production. Also the average soil profile salt concentration increased by 10% as irrigation water level increases from W4 to W5 treatment with the same water quality. Leaching with water having salinity more than the threshold value will increase average root zone salinity and significantly affect crop yield and growth. The effect of the interaction (combination) between irrigation water quantity and quality on lemon fruits yield of the second productive year (2000) can be summarized as follows: Rank
Water level irrigation water salinity (dS/m)
1 2 2 3 4 4 5 5 6 6 7
1.00Td 1.50Td 0.75Td 1.00Td 1.50Td 0.50Td 0.75Td 1.00Td 0.50Td 1.50Td 0.75Td
(W4) (W5) (W3) (W4) (W5) (W2) (W3) (W4) (W2) (W5) (W3)
1.33 1.33 1.33 3.10 3.10 1.33 3.10 4.88 3.10 4.88 4.88
0.059 0.059 0.059 0.159 0.159 0.059 0.159 0.319 0.159 0.319 0.319
Lemon fruits yield (kg per tree) (S1) (S1) (S1) (S2) (S2) (S1) (S2) (S3) (S2) (S3) (S3)
32.9 24.6 23.9 19.7 15.8 15.3 10.2 10.5 6.3 6.2 3.4
aa b b c d d e e f f g
a Values with the same letter are not significantly different at 5% probability level using Duncan's multiple range test.
At S1 treatment, deficit irrigation (W3 treatment) has an adverse effect on lemon fruit production due to lack of water as excess irrigation in W5 treatment due to nutrient leaching. The fruit yield of treatments W2S1 (15.3 kg per tree) and W5S2 (15.8 kg per tree) was the same. The low yield of W2S1 treatment was due to lack of water while the low yield for treatment W5S2 was due to high salinity and nutrient leaching. The same trend was at W2S2 and W5S3 treatments. Although crop water use (Etc) was the same at treatments W3S1 and W4S3, fruit yield in W4S3 significantly reduced by about 56% as compared to W3S1 treatment due to high salinity. Irrigation water salinity is very important factor that should be managed with limited (deficit) irrigation. Also, increasing amount of applied saline water could result in a negative effect on crop yield and environment such as increasing average root zone salinity, nutrient leaching, water logging, increasing the drainage water load of salinity which might pollute ground water and other water sources.
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4. Conclusions Increasing irrigation water salinity increased salt concentration and osmotic potential in the root zone and consequently reduced lemon annual water use, stem diameter and fruits yield. The percentage shaded area significantly increased with time being 1.11, 2.89, 5.17, 15.8 and 22.34% in the first, second, third, fourth and the fifth years, respectively. The first 3 years were devoted for adaptation and root development, and the significant vegetative growth started with the fourth year and consequently water requirement. The significant increase in stem diameter was in the first two years being about 3±4 times higher than that at planting, and continued to increase but in a decreasing increment for the following years. Lemon fruits were harvested for the first time about 44 months from planting date. Without supplemental irrigation, lemon trees cannot survive the first year even with a total rainfall of 274 mm. Regardless of irrigation water salinity, the significantly highest fruit yield was at irrigation water depth equal to evaporation depth from class A pan when corrected for tree canopy percentage shaded area. Acknowledgements This research was sponsored by the Deanship of Scientific Research at the University of Jordan, Amman, Jordan. References Abu-Awwad, A.M., Hill, R.W., 1990. Tomato production and soil salt distribution under line-source trickle irrigation. J. Agronomy Crop Sci. 167, 188±195. Ayers, R.S., Westcot, D.W., 1985. Water quality for agriculture. Irrig. Drain. Paper no. 29, Rev. 1. FAO, Rome, Italy. Bielorai, H., Shalhevet, J., Levy, Y., 1978. Grapefruit response to variable salinity in irrigation water and soil. Irrig. Sci. 1, 61±70. Cerda, A., Nieves, M., Guillen, M.G., 1990. Salt tolerance of lemon trees. Irrig. Sci. 11, 245±249. Cole, P.J., McLeod, P.I., 1985. Salinity and climatic effects on the yield of citrus. Aust. J. Exp. Agric. 25, 711± 721. Chartzoulakis, K., Michelakis, N., Stefanoudaki, E., 1999. Water use, growth, yield and fruit quality of Bonanza oranges under different soil water regimes. Adv. Hort. Sci. 13, 6±11. Doorenbos, J., Kassam, H.A., 1979. Yield response to water. Irrig. Drain. Paper no. 33. FAO, Rome, Italy. Ghassemi, F., Jakeman A.J., Nix, H.A., 1995. Salinization of Land and Water Resources. University of New South Wales Press, Sydney, Australia, 526 pp. Green, G.C., Moreshet, S., 1979. An analysis of seasonal water use characteristics of Valencia orange trees in the Sundays River Valley. Crop Prod. VIII, 179±183. Keller, J., Bliesner, D.R., 1990. Sprinkler and Trickle Irrigation. Van Nostrand-Reinhold, New York. Levy, Y., Shalhevet, J., 1990. Ranking the salt tolerance of citrus rootstocks by juice analysis. Scientia Hort. 45, 89±98. Marschner, H., 1997. Mineral Nutrition of Higher Plants, 2nd Edition. Academic Press, 24±28 Oval Road, London NW1 7DX. Mass, E.V., 1986. Salt tolerance of plants. Appl. Agric. Res. 1, 12±26. Mass, E.V., 1993. Salinity and citrus culture. Tree Physio. 12, 195±216.
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Mass, E.V., Hoffman, G.J., 1977. Crop salt tolerance-current assessment. Proc. W. Soc. Civ. Eng.: J. Irrig. Drain. Div. 103 (TR2), 115±134. Ministry of Agriculture, 1998. Annual Report. Amman, Jordan, 108 pp. Nastou, A., Chartzoulakis, K., Therios, I., Bosabalidis, A., 1999. Leaf anatomical response, ion content and CO2 assimilation in three lemon cultivas under NaCl salinity. Adv. Hort. Sci. 13, 61±67. Shalhevet, J., 1994. Using water of marginal quality for crop production: major issues. Agric. Water Manage. 25, 233±269. Shalhevet, J., Yaron, D., Horowitz, M., 1974. Salinity and citrus yield. An analysis of results from a salinity survey. J. Hort. Sci. 49, 15±27.
In¯uence of different water quantities and qualities on lemon trees and soil salt distribution at the Jordan Valley A.M. Abu-Awwad* Department of Agricultural Resources and Environment, Faculty of Agriculture, University of Jordan, Amman, Jordan Accepted 26 March 2001
Abstract The in¯uences of water quantity and quality on young lemon trees (Eureka) were studied at the University of Jordan Research Station at the Jordan Valley for 5 years (1996±2000). Five water levels and three water qualities were imposed via trickle irrigation system on clay loam soil. The primary effect of excess salinity is that it renders less water available to plants although some is still present in the root zone. Lemon trees water requirements should be modi®ed year by year since planting according to the percentage shaded area, and this will lead into substantial water saving. Both evaporation from class A pan and the percentage shaded area can be used to give a satisfactory estimate of the lemon trees water requirement at the different growth stages. The highest lemon fruit yield was at irrigation water depth equal to evaporation depth from class A pan when corrected for tree canopy percentage area. Increasing irrigation water salinity 3.7 times increased average crop root zone salinity by about 3.8±4.1 times. The high salt concentration at the soil surface is due to high evaporation rate from wetted areas and the nature of soil water distribution associated with drip irrigation system. Then, the salt concentration decreased until the second depth, thereafter, salt concentration followed the bulb shape of the wetted soil volume under trickle irrigation. Irrigation water salinity is very important factor that should be managed with limited (de®cit) irrigation. But increasing amount of applied saline water could result in a negative effect on crop yield and environment such as increasing average crop root zone salinity, nutrient leaching, water logging, increasing the drainage water load of salinity which might pollute ground water and other water sources. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Lemon; Shaded area; Water requirement; Salinity; Jordan
*
Tel.: 962-6-5355000/ext. 2564; fax: 962-6-5355577. E-mail address: [email protected] (A.M. Abu-Awwad). 0378-3774/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 1 2 2 - 6
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1. Introduction Jordan Valley (JV) is located in the Rift Valley, which extends from east Africa to Turkey. It is divided into three parts; North, Middle, and South. The Northern part extends from Tebris Lake to Deir Alla, the Middle JV starts from Deir Alla to the Dead Sea and the Southern JV is extended from Dead Sea to gulf of Aqaba. The climate, soils, and water resources are varied widely among the three parts. The average annual rainfall at the Northern Shuna is about 350, 280 mm at Deir Alla, and 35 mm at Aqaba. Total irrigated land in the JV is about 30,000 ha. Only 23,000 ha currently receive water due to scarce water supply. Water resources in the Kingdom of Jordan are very limited. Irrigation in the JV consumes about 340 million cubic meters. Increasing water demand for domestic use has put a burden on agricultural expansion. The agriculture sector consumes about 75% of the total available water, but its contribution to the gross national income is limited. Due to limitation of water resources in Jordan, marginal quality water has been used for irrigation. For 2010, it is anticipated that marginal water will constitute more than 30% of the available water resources for irrigation. Using such low quality water for irrigation is not possible without adverse impact on the environment and agroecosystem. Soil degradation and pollution of soil, water and agricultural crops are of major concern to the agricultural sector. Therefore, proper management of low quality water is a prerequisite for successful and sustainable farming. The Jordan Valley is the most important irrigated area in Jordan where the lands are used for cultivation of citrus and vegetable production. The Ministry of Agriculture in Jordan (1998) indicated that the total lemon productive area was 1568.6 ha produced 42279 tonnes. About 82.2% of the lemon cropped area concentrated in the JV and produced 90% of Jordan total production. The climatic conditions allow production of out of season agricultural products. Thus, the area is used for exporting vegetables and citrus to Europe and the Gulf countries in winter. Crop production in the arid and semi-arid region is dependent on irrigated agriculture. Under these conditions the farmers are obliged to use irrigation water with high quantities of dissolved salts, invariably accompanied by yield reductions of most crops. Extensive areas of irrigated land have been and are increasingly becoming degraded by salinization and water logging resulting from over irrigation and other forms of poor agricultural management (Ghassemi et al., 1995). The best estimate of the effective salinity when salt is non-uniformly distributed with depth is the mean salinity within the root zone. Crop water production functions relating yield to evapotranspiration are not influenced by water salinity (Shalhevet, 1994). Soils are considered saline if they contain soluble salts in quantities sufficient to interfere with the growth of most crop species. This, however, is not a fixed amount of salt but depends on plant species, the soil texture and water capacity of the soil, and the composition of the salts. According to the definition of US Salinity Laboratory, the saturation extract of a saline soil has an electrical conductivity (ECe) greater than 4 dS/m and an exchangeable sodium percentage (ESP) of less than 15. Plant species differ greatly in their growth response to salinity (Marschner, 1997). Grapefruit and orange threshold ECe values were about 1.7±1.8 dS/m and the rate of yield reduction was about 16% per dS/m. These data were obtained under steady-state
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
55
conditions with available crop varieties. The conditions were uniform salt distribution with depth, small changes with time, unrestricted water supply (heavy leaching), and flood irrigation. Initially the crops were established with non-saline water (Mass, 1986). In practice, under realistic field conditions, uniformity is the exception rather than the rule. Furthermore, crops may have different sensitivities at different stages of growth. In saline substrates Na and Cl are usually the dominant ions. Despite the essentiality of chloride as a micronutrient for all higher plants and of Na as mineral nutrient for many halophytes, the concentrations of both ions in saline substrates by far exceed this demand and lead to toxicity in non-salt-tolerant plants. In many herbaceous crop species, e.g. grapevine and many fruit trees, growth inhibition and injury of the foliage occur even at low levels of NaCl salinization. Under such conditions, water deficit is not a constraint and at least for citrus species, high chloride sensitivity and thus toxicity is the major constraint (Mass, 1993). Green and Moreshet (1979), using weighing lysimeters to measure daily ET concluded that the crop factor I/Ep (I and Ep are irrigation water and pan evaporation in millimeter, respectively), when corrected for atmospheric resistance variations represents real tree conductance and can be used for irrigation scheduling. Chartzoulakis et al. (1999) indicated that orange (Bonanza) canopy diameter, plant height and trunk diameter were not significantly different in 0.01 and 0.05 MPa soil water potentials treatments, but were significantly reduced at 1.5 MPa soil water potential. Lemon tree is a salt-sensitive crop to salinity (Cerda et al., 1990; Mass and Hoffman, 1977) and even low salt concentrations may affect its growth and productivity (Shalhevet et al., 1974; Cole and McLeod, 1985; Levy and Shalhevet, 1990). Nastou et al. (1999) indicated that higher salinity in the rooting medium significantly reduced the shoot length. However, the extent of this reduction was different for each cultivar. The yield of mature grapefruit trees was reduced by 13.5% as electrical conductivity of the soil saturation extract increased 1.0 dS/m above a threshold value of 1.2 dS/m (Bielorai et al., 1978). Also, they indicated that total water uptake was reduced as salt concentration in the soil increased. A considerable amount of data is available regarding the effect of irrigation water and soil salinity on crop yield. But, most of the data was obtained with crop established prior to the introduction of saline conditions. In addition, crops may have different sensitivities at different stages of growth and the duration of exposure (Shalhevet, 1994). However, available data for citrus trees in general are limited and almost negligible for lemon. Therefore, a field experiment was conducted to investigate the influence of different water and salinity levels on the development of young lemon (Eureka) trees (since planting), under the Jordan Valley conditions. 2. Materials and methods A field experiment was conducted for 5 years from 1996 to 2000 at the Experimental Research Station of the University of Jordan in the Jordan Valley on lemon (Citrus Limon [L.] Burm. F.) Eureka. The site represents areas of Jordan characterized by low rainfall falling in the winter season (November to April). The climates of the area being characterized by hot summer and warm winter. The annual rainfall ranges between 40 and
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A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
Table 1 Some physical and chemical properties of the soil at the experiment sitea Soil depth (cm)
Clay (%)
Silt (%)
Sand (%)
Texture class
SG
FC (Pv%)
PWP (Pv%)
ECe (dS/m)
0±20 20±40 40±60 60±80
31.8 38.4 35.0 35.2
30.9 22.6 29.3 26.1
37.3 39.0 35.7 38.7
Clay Clay Clay Clay
1.47 1.52 1.49 1.57
27.4 28.5 29.1 27.0
10.5 10.2 11.3 11.2
1.1 1.1 1.1 1.1
loam loam loam loam
0.021b 0.021 0.021 0.021
a SG: specific gravity, FC: field capacity, PWP: permanent wilting point, ECe: paste extract electrical conductivity. b 0.021 is the standard deviation.
274 mm, with an average rainfall of 154 mm during the period of 1996±2000. January is the coolest month of the year, while August is the warmest month. Some physical and chemical properties of the experiment site soil are presented in Table 1. Field capacity (280 mm/m) and permanent wilting point (108 mm/m) were estimated in the laboratory for each soil depth on undisturbed soil samples using the ceramic plate apparatus at 0.3 and 15 bars, respectively. Field capacity for the first soil layer was also determined and checked in the field. One-year-old lemon seedlings were planted on the 15 March 1996 at a spacing of 5 m 5 m. The experimental design was factorial completely randomized block, with three replications. The soil was clay loam (35.1 and 27.2% clay and silt, respectively) with good natural drainage. Drip irrigation was used with one dripper per tree for the first year, two drippers 1.0 m apart per tree for the second year and thereafter four drippers 1.0 m apart (zigzag lateral for each tree) were used per tree. The drippers were Controlled Palm emitter types of 8 lph. The experiment consisted of five water levels and three water qualities. The average daily rate of transpiration under trickle irrigation is a function of conventionally computed average rate of daily consumptive use and the extent of the plant canopy (shaded area). A relatively simple relation (Keller and Bliesner, 1990) that serves for this estimate is Pd Pd Td Ud 0:15 1:0 (1) 100 100 where Td is the average transpiration rate for a crop under trickle irrigation, Ud the conventionally computed average daily consumptive use rate (in this study the average daily class A pan evaporation (Ep) is used), and Pd is the ground area within the drip line shaded by the crop canopies at midday as a percentage of the total ®eld area (%). The ®ve water levels: W0 0:0, W1 0:25, W2 0:5, W3 0:75, W4 1:0 and W5 1:5 times W4 (W4 T d as calculated by Eq. (1)). The three water qualities: S1 irrigation water from King Abdulah canal with an average salinity of 1.33 dS/m, S2 mixed irrigation water from irrigation water and drainage water with an average salinity of 3.10 dS/m, and S3 drainage water with an average salinity of 4.88 dS/m. The shaded area was only measured in W4S1 treatment to quantify irrigation water requirements for the expected reference trees with fresh irrigation water. Pd was measured by marking off the area allocated to a tree (5 m 5 m) in the field and
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measuring the shaded area using a 0.2 m grid system on monthly basis at midday. Irrigation was practiced weekly (May to November). For each irrigation level, three access tubes were installed around one tree at 0.5, 1.0 and 1.5 m from the tree trunk to a depth of 1.0 m. Soil moisture was measured weekly just before the irrigation event using field calibrated neutron probe at depth increments of 0.20 m from a depth of 0.10 m to a depth of 0.90 m. Soil moisture at the surface layer (0± 0.20 m) was determined using the gravimetric method. Class A pan evaporation measured on site, for the period between two irrigation events was used to quantify the required amount of irrigation water to be added for each treatment. The experiment was started with the soil water content near field capacity. Soil water depletion (crop evapotranspiration, Etc) for the period between irrigation was estimated from the soil water content measurements. During short periods when field capacity was reached and/or exceeded due to water applied, drainage water was estimated from dEtc d2
d1
d2 d1 dw ; where d2 dFC dD 0:0 if d2 > dFC ; then d2 dFC and dD d w
dFC
d1 dw
dEtc
where dEtc is the measured soil water depletion depth, d1 and d2 the equivalent depths of moisture in the root zone just before and after irrigation, respectively, dD the drainage water depth, and dw the water (irrigation plus precipitation) depth applied. Lemon tree stem diameter and shaded area were measured monthly. Irrigation water salinity was measured weekly directly after each irrigation event. Lemon fruits (yield) were harvested and weighed at the ripen time. The soil profile at three locations (0.5, 1.0 and 1.5 m from the tree trunk) was divided into four soil layers (0±0.2, 0.2±0.4, 0.4±0.6, and 0.6±0.8 m). Representative soil samples were collected from each grid, and composite samples of the 12 grids for each profile were prepared. The electrical conductivity of the soil saturation paste extract (ECe) was determined. 3. Results and discussions 3.1. Irrigation water quantity and quality The amount of rainfall, evaporation and applied irrigation water are presented in Table 2. Ayers and Westcot (1985), classified water qualities according to their effects on crop water availability into <0.7, 0.7±3.0 and >3.0 dS/m as none, slight to moderate and severe, respectively. For each irrigation water salinity treatment used in this study, variations in irrigation water salinity were not significant and almost constant for the last 5 years. Fresh irrigation water (S1) treatment salinity varies from 1.21 to 1.46 with an average of 1:33 0:059 dS/m (slight to moderate restriction on use). While, irrigation water salinity in S2 and S3 treatments varies from 2.80 to 3.34 with an average 3:10 0:159 dS/m (moderate to severe restriction on use) and from 4.33 to 5.33 with an
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Table 2 Amounts of applied irrigation water to lemon trees for each water level, for the 5 years (1996±2000) Rainfall R (mm) a
274
Ep (mm)
1444
Water levels
1996±1997 I
W0 W1 W2 W3 W4 W5
b
0 58 115 173 230 345
Kp
c
0.00 0.04 0.08 0.12 0.16 0.20
167
40
133
1991
1875
1653
1575
1997±1998
1998±1999
1999±2000
2000
I
Kp
I
Kp
I
Kp
I
Kp
0 88 175 263 351 526
0.00 0.04 0.09 0.13 0.18 0.27
0 91 181 272 363 544
0.00 0.05 0.10 0.15 0.19 0.29
0 117 235 352 470 704
0.00 0.07 0.14 0.21 0.28 0.43
0 123 246 370 493 739
0.00 0.08 0.16 0.23 0.31 0.47
a
Ep represents class A evaporation only during the irrigation period. I: irrigation water applied (mm). c Kp is the crop factor (I/Ep). b
average of 4:88 0:319 dS/m (severe restriction on use), respectively. Chemical analysis for both fresh (S1) and saline (S3) irrigation water qualities on 17 May 2000 was as follows: Parameter
Fresh irrigation water (S1)
Saline irrigation water (S3)
Specific conductance (dS/m) Laboratory pH (units) Calcium by titration (mg/l) Magnesium by calculation (mg/l) Sodium by flame photometry (mg/l) Potassium by flame photometry (mg/l) Chloride by titration (mg/l) Sulfate (mg/l) CO3 by titration (mg/l) Bicarbonate, H2SO4 by titration (mg/l) Nitrate by spectrophotometer (mg/l) Sodium adsorption ratio (SAR)
1.16 7.73 58.9 30.9 123.5 16.0 194.8 93.1 0.0 216.9 20.0 3.23
4.86 7.95 178.0 156.4 699.0 72.1 1206.9 836.9 0.0 153.5 55.8 9.2
3.2. Soil salt distribution With irrigation water salinity of 1.33 dS/m (S1) the average soil profile salinity (ECe) is relatively low and less than 2 dS/m for the three irrigation water levels (W3, W4 and W5). Soil salinity classified as non-saline in which salinity effects are negligible, according to guidelines for soil salinity classes and crop growth (Ayers and Westcot,
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Table 3 Soil salt distribution (ECe in dS/m) as influenced by S1 irrigation water salinity at W3 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
1.6 1.2 1.1 1.0
1.6 2.7 1.7 1.0
1.4 1.2 1.2 1.0
1.53 1.70 1.33 1.0
1.23
1.75
1.20
1.39
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
1985). The average ECe along the soil profile at the same three irrigation water treatments indicates that salt concentration still below the steady-state (ECe 1:5ECiw), might be due to the positive effect of winter rainfall (481 mm). Tables 3±5 show the soil salt distribution and concentration along the soil profile at W3, W4 and W5 irrigation water treatments, respectively, using S1 irrigation water salinity. The general salt profile at the three water treatments followed the typical Table 4 Soil salt distribution (ECe in dS/m) as influenced by S1 irrigation water salinity at W4 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
1.3 1.4 1.1 1.1
2.4 1.8 4.5 1.6
1.2 1.1 1.5 0.9
1.63 1.43 2.37 1.2
1.23
1.58
1.18
1.66
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
Table 5 Soil salt distribution (ECe in dS/m) as influenced by S1 irrigation water salinity at W5 water levels (2000)a Distance from tree trunk (m)
Average a
Average
0.5
1.0
1.5
1.4 1.3 1.4 1.1
2.1 2.4 5.3 1.9
1.3 1.0 1.4 1.2
1.60 1.57 2.7 1.4
1.3
2.93
1.23
1.82
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
60
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
steady-state salt distribution under trickle irrigation (bulb shape) with maximum ECe was at 1.0 m from the tree trunk. Salts accumulated at the soil surface were due to the nature of trickle irrigation method and wet soil surface evaporation. At the soil surface, salt concentration increased from 1:1 0:021 dS/m (initial soil salt concentration, March 1996) to an average of 1.53, 1.63 and 1.6 dS/m at W3, W4 and W5 treatments (March 2000), respectively. At W3 treatment the highest salt concentration being 2.7 dS/m at a distance of about 1.0 m from the tree trunk at the second soil layer (0.2±0.4 m), might be due to the limited amount of applied irrigation water (Table 2). While, soil salts concentration were the highest (4.5 and 5.3 dS/m) at the third soil layer (0.4±0.6 m) of the same distance from tree trunk in W4 and W5 treatments, respectively. Amounts of applied irrigation water in these treatments were high enough to cause some leaching to a deeper soil layer. The low salt concentration at the fourth soil layer (0.6±0.8 m) is due to the nature of the bulb wetting under trickle irrigation system. At S3 treatment soil salt distribution followed the same trend as in S1 treatment at the different water levels. Irrigation water salinity in S3 treatment was almost 3.7 times higher than irrigation water salinity in S1 treatment, and consequently increased average root zone salinity by about 3.8, 4.1 and 4.1 times at W3, W4 and W5 treatments, respectively (Tables 6±8). The average root zone salinity at S3 treatment was 5.32, 6.84 and 7.55 dS/m in W3, W4 and W5 treatments, respectively. Soil salinity classified as moderately saline where yields of Table 6 Soil salt distribution (ECe in dS/m) as influenced by S3 irrigation water salinity at W3 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
4.8 4.3 4.9 2.6
8.4 9.0 6.8 3.6
8.1 4.1 4.2 3.0
7.1 5.8 5.3 3.1
4.15
6.95
4.85
5.32
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
Table 7 Soil salt distribution (ECe in dS/m) as influenced by S3 irrigation water salinity at W4 water levels (2000)a Distance from tree trunk (m)
Average a
Average
0.5
1.0
1.5
4.3 5.2 4.8 3.5
10.2 6.1 14.8 6.0
6.4 5.9 8.4 6.5
6.97 5.73 9.33 5.33
6.8
6.84
4.45
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
9.28
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61
Table 8 Soil salt distribution (ECe in dS/m) as influenced by S3 irrigation water salinity at W5 water levels (2000)a Distance from tree trunk (m)
Average
Average
0.5
1.0
1.5
5.5 5.7 5.2 6.3
12.6 7.2 11.9 8.2
8.0 6.7 7.1 6.2
8.7 6.53 8.07 6.9
4.85
7.55
4.15
6.95
a
Soil depth (m): 0.0, 0.2, 0.4, 0.6, 0.8.
many crops are restricted (Ayers and Westcot, 1985). Except at the soil surface the highest salt concentration was at 0.2±0.4 (9.0 dS/m), 0.4±0.6 (14.8 dS/m) and 0.4±0.6 m (11.9 dS/m) soil layer in W3, W4, and W5 treatments, respectively, with S3 treatment at 1.0 m distance from the tree trunk. The average root zone salt concentration was less than expected salt concentration at steady-state in W3 and W4 treatments, however, it reached the expected steady-state salt concentration at W5 treatment due to continues excess irrigation. The same soil salt distribution pattern was noticed at the third distance (1.5 m from the tree trunk) as at 1.0 m distance, but with lower salt concentrations. The high salt concentration being at the soil surface is due to high evaporation rate from the wetted area, then salt concentration decreased until the second depth, thereafter, salt concentration followed the bulb shape of the wetted soil volume under trickle irrigation. At the 0.5 m distance from the tree trunk, soil salt concentration (ECe) significantly decreased and was almost uniform at all depths. The low salt concentration was due to the excessive amount of irrigation water applied close to the trickle point source causing leaching of salts. 3.3. Water uptake Table 9 illustrates the seasonal water balance components for the 1999 and 2000 growing seasons. For both 1999 and 2000 growing seasons, the highest water use was in W5S1 treatment being 546 and 606 mm/year, followed by 517 and 591 mm/year, respectively, in W4S1 treatment. During 1999 increasing irrigation water salinity from 1.33 to 3.1 and 4.88 dS/m reduced annual water use by about 8 and 10%, respectively, in W4 treatment, and by 18 and 14%, respectively, in W5 treatment. The effects of irrigation water salinity were even more pronounced in the fifth year (2000), when lemon annual water use reduced by about 18 and 25% as irrigation water salinity increased from 1.33 to 3.1 and 4.88 dS/m, respectively, at W4 and W5 treatments. Thus, the primary effect of excess salinity is that it renders less water available to plants although some is still present in the root zone. This is because the osmotic potential of soil solution increases as the salt concentration increases (Abu-Awwad and Hill, 1990; Ayers and Westcot, 1985).
62
Treatment
S1 W1
Desired irrigation (fraction of Td) 1999 Irrigation depth (mm) Rainfall depth 40 (mm) Drainage depth (mm) Annual change in soil moisture (mm) Annual water use (Etc)b (mm) 2000 Irrigation depth (mm) Rainfall depth 133 (mm) Drainage depth (mm) Annual change in soil moisture (mm) Annual water use (Etc)b (mm) a b
0.25
S2 W2 0.5
W3 0.75
W4 1.0
W5 1.5
W1 0.25
S3 W2 0.5
W3 0.75
W4 1.0
W5 1.5
W1
W2
0.25
0.5
W3 0.75
W4 1.0
W5 1.5
0a
235
352
470
704
0a
235
352
470
704
0a
0a
352
470
704
± ± ±
2 1 274
5 3 390
11 18 517
160 38 546
± ± ±
0 12 263
0 17 375
2 31 477
244 55 445
± ± ±
± ± ±
0 24 368
0 43 467
250 57 471
0a
246
370
493
739
0a
246
370
493
739
0a
0a
370
493
739
± ± ±
0 14 365
13 18 472
15 20 591
220 46 606
± ± ±
25 11 343
67 16 420
82 41 503
290 68 514
± ± ±
± ± ±
68 31 404
105 46 475
294 95 483
No irrigation water was applied (there were no trees). Estimated from soil water content measurements.
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Table 9 Estimated seasonal water balance components for the years of 1999 and 2000
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63
With deficit irrigation, increasing irrigation water increased available water for transpiration and evaporation. The increase in transpiration was dominant with the limited available water (W0 to W4), while evaporation and drainage were dominant in the higher water level treatment (W5). In S1 and S2 treatments, the percentage increase in annual water use was in proportion with percentage increase in irrigation water applied as irrigation water level increased from W1 to W4. Increasing irrigation water will increase water use up to the potential Etc, after which increasing irrigation water will not significantly affect Etc. Doorenbos and Kassam (1979) reported that crop water requirement for mature citrus is in the range of 900±1200 mm/growing periods. Results indicate that water requirement for lemon trees, even at the fifth year from planting, is still about half the quantity suggested by Doorenbos and Kassam (1979). 3.4. Shaded area Fig. 1 illustrates the change in the mean monthly Pd with time for lemon trees. In the first year (1996), there was no significant increases in the mean monthly Pd. While during 1997 there was a significant increase in the Pd, before pruning. Pruning was done for the first time in August of the second year (1997). In the third year (1998), shaded areas significantly increased during the year with maximum Pd in October. In the fourth year (1999), shaded area was about 3, 5 and 15 times significantly higher than in the years of 1998, 1997 and 1996, respectively. There was no significant change with time in shaded area during 1999. This might be due to the flowering that was started during the third year and harvesting of lemon fruits was carried out late the same year. Also, annual rainfall was very low being 40 mm during the winter season of 1999 compared to 274 and 167 mm annual rainfall of 1997 and 1998 winter seasons, respectively (Table 2). On the fifth year (2000), lemon trees shaded area significantly increased as compared with the past 4 years (1996±1999). The significant increase in the shaded area started early on the month of July, and significantly increased with time along the growing season. The highest shaded area being 23.7% during the month of September 2000. The average percentage shaded area significantly increased with time being 1.11, 2.89, 5.17, 15.8 and 22.34% in the first, second, third, fourth and the fifth years, respectively. Consequently, the average amount of irrigation water applied increased each year in all treatments, as plants were growing (Table 2). In W4 treatment, the crop factor I/Ep was about 0.16 increasing to 0.18 and to 0.19 for the second and third years, respectively. In the fourth and fifth years, the crop factor increased to 0.28 and 0.31, respectively (about 1.5±1.6 times that in the third year). This indicates that the first 3 years were devoted for adaptation and root development, and the significant vegetative growth started with the fourth year and consequently water requirement. Applied irrigation water increased by 53, 58, 104 and 114% in the second, third, fourth and fifth years, respectively, as compared to amount of applied during the first year. Without supplemental irrigation, lemon trees cannot survive the first year with a total rainfall of 274 mm. In W1 treatment, supplementing winter rainfall with 25% of Td evaporation during the summer months (May to October) using S1 and S2 water qualities succeed to maintain lemon trees alive for the first 3 years (1996 to 1998) and only for the first 2 years (1996±1997) using S3 water quality. Due to poor water quality (high salinity) in S3 treatment, supplementing
64 A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
Fig. 1. Mean monthly lemon trees shaded area (%) for treatment W4S1.
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
65
winter rainfall with 50% of Td hardly succeeded to maintain lemon trees alive for the first 3 years, but not with S1 and S2 water quality treatments. Owing to the dry winter (40 mm) of 1998/1999 winter season, most of the stressed lemon trees died in the third year. Thus, evaporation from class A pan when corrected for tree canopy percentage shaded area can represent a good estimate of lemon trees water requirement. 3.5. Stem diameter Table 10 illustrates the influence of different water quantities and qualities on lemon tree stem diameter. During 1996, stem diameter varies from a minimum of 12 mm in W1 with S3 treatment to a maximum of 17 mm in W4 with S2 treatment. With deficit irrigation, increasing amount of applied irrigation water partially compensated for the adverse effect of irrigation water salinity, and consequently increased lemon tree stem diameter. In S1 irrigation water quality, although amount of applied irrigation water increased from W2 to W5 stem diameter was almost the same for the first 4 years (1996± 1999), but was significantly higher than that in W1 water treatment. However, in the fifth year (2000), stem diameter starts to increase more in the higher water level treatments, Table 10 Stem diameter as influenced by irrigation water quantity and qualitya Water levels W1
W2
W3
W4
W5
1996 S1 S2 S3
13.3 bcd 13.7 bcd 12.0 d
16.3 ab 16.0 ab 12.3 cd
15.3 abc 16.0 ab 13.7 bcd
16.0 ab 17.0 a 15.0 abcd
14.3 abcd 16.3 ab 14.7 abcd
1997 S1 S2 S3
11.7 cd 25.0 abc 6.3 d
30.3 ab 25.7 abc 5.7 d
36.0 a 29.3 ab 16.7 bcd
33.0 ab 36.0 a 28.7 ab
32.3 ab 33.0 ab 26.3 abc
1998 S1 S2 S3
14.0 de 10.3 de 0e
51.0 ab 37.3 bc 7.3 de
56.3 ab 44.0 abc 22.3 cd
63.0 a 55.7 ab 44.7 ab
53.0 ab 50.3 ab 39.0 bc
1999 S1 S2 S3
0e 0e 0e
71.3 abc 52.7 cd 0e
77.3 ab 58.3 bcd 16.0 e
82.7 a 71.7 abc 64.3 abcd
81.0 a 73.3 abc 47.7 d
2000 S1 S2 S3
0e 0e 0e
76.0 abcd 58.7 cd 0e
86.3 ab 62.7 bcd 16.7 e
87.3 a 76.7 abcd 70.3 abcd
90.0 a 80.7 abc 55 d
a
For each year, values with the same letter are not significantly different at 5% probability level using Duncan's multiple range test.
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A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
but not significantly. Almost the same trend was in S2 irrigation water salinity. With S3 irrigation water salinity, the significantly highest stem diameter was in W4 water level treatment and was reduced not significantly in W5 treatment. In the fifth growing season (2000), stem diameter was the highest in W5 treatment at S1 (90 mm) and S2 (80.7 mm) treatments but was not significantly higher than that in W2, W3 and W4 water levels. However, in S3 water quality treatment stem diameter (70.3 mm) was the highest in W4 water level treatment, but was not significantly higher than stem diameter (55 mm) in W5 water level treatment. In general, the significant increase in stem diameter was in the first 2 years (3±4 times stem diameter at planting) and continued to increase but in a decreasing increment for the following years. 3.6. Lemon yield Lemon fruits were harvested for the first time on the month of November 1999, about 44 months from planting date. The influence of irrigation water quantities and qualities on fruit yield of the year 1999 is illustrated in Fig. 2. Regardless of irrigation water salinity, lemon production was a complete failure in W0 and W1 treatments. Increasing amount of applied irrigation water in W2 treatment to double the amount applied in W1 treatment gave 16.7, 5.3, and 0.0 kg per tree of lemon fruit yield in S1, S2 and S3 treatments, respectively. In S1 treatment, increasing irrigation water level from W2 to W3, W4 and W5 treatments did not affect lemon fruit yield, with a slight non-significant decrease at W5. However, in S2 and S3 treatments, increasing amount of applied irrigation water substantially but non-significantly increased lemon fruit yield. With S2 irrigation water salinity lemon fruit yield increased from 0.0 to 5.3, 8.9, 13.9, and 10.3 kg per tree as irrigation water level increased from W1 to W2, W3, W4, and W5 treatments, respectively. The same trend was in S3 treatment (Fig. 2), but there was no yield in W2 treatment and yield non-significantly increased to 2.8, 4.5 and 1.6 kg per tree as irrigation water level increased from W2 to W3, W4 and W5 treatments, respectively. In general, with the same irrigation water salinity the highest yield was obtained in W4 treatment being 17.0, 13.9, and 4.5 kg per tree in S1, S2, S3 treatments, respectively. In S1 treatment at all water levels but W1, lemon fruit yield was significantly higher than that in S3 treatment (Fig. 2). Lemon fruit yield in S1 treatment was consistently but not significantly higher than that in S2 treatment at all water levels but in W2. During 2000 growing season, lemon fruits were harvested two times (August and November). Fruit yield as influenced by irrigation water quantity and quality is illustrated in Fig. 3. The significantly highest yield (32.9 kg per tree) was in W4S1 treatment. Increasing irrigation water level from W1 to W2, W3 and W4 treatments significantly increased (almost linearly) fruit yield in all salinity treatments. However, lemon fruit significantly reduced as irrigation water level increases from W4 to W5 treatment at all salinity treatments. Crop production functions that describes the response of lemon fruit yield to amount of irrigation water applied as a percent of Td (Eq. (1)) were developed at the three salinity treatments (2000), and regression analysis gave the following relationships: LFY
21:55 95:21W
42:77W 2 ;
r 2 0:97 at S1 treatment
(2)
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
Fig. 2. Influence of irrigation water quantities and qualities on Lemon yield (1999).
67
68 A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
Fig. 3. Influence of irrigation water quantities and qualities on Lemon yield (2000).
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
LFY LFY
11:39 46:24W 22:67 55:83W
18:44W 2 ; 2
24:27W ;
69
r 2 0:89 at S2 treatment 2
r 0:79 at S3 treatment
(3) (4)
where LFY is the lemon fruit yield in kilogram per tree and W is the percentage of Td (i.e. 0.25, 0.5, 0.75, etc.). Increasing the amount of applied irrigation water more than that applied in W4 treatment might leached salts to a deeper soil layer but also leached plant nutrients, which may affected crop production. Also the average soil profile salt concentration increased by 10% as irrigation water level increases from W4 to W5 treatment with the same water quality. Leaching with water having salinity more than the threshold value will increase average root zone salinity and significantly affect crop yield and growth. The effect of the interaction (combination) between irrigation water quantity and quality on lemon fruits yield of the second productive year (2000) can be summarized as follows: Rank
Water level irrigation water salinity (dS/m)
1 2 2 3 4 4 5 5 6 6 7
1.00Td 1.50Td 0.75Td 1.00Td 1.50Td 0.50Td 0.75Td 1.00Td 0.50Td 1.50Td 0.75Td
(W4) (W5) (W3) (W4) (W5) (W2) (W3) (W4) (W2) (W5) (W3)
1.33 1.33 1.33 3.10 3.10 1.33 3.10 4.88 3.10 4.88 4.88
0.059 0.059 0.059 0.159 0.159 0.059 0.159 0.319 0.159 0.319 0.319
Lemon fruits yield (kg per tree) (S1) (S1) (S1) (S2) (S2) (S1) (S2) (S3) (S2) (S3) (S3)
32.9 24.6 23.9 19.7 15.8 15.3 10.2 10.5 6.3 6.2 3.4
aa b b c d d e e f f g
a Values with the same letter are not significantly different at 5% probability level using Duncan's multiple range test.
At S1 treatment, deficit irrigation (W3 treatment) has an adverse effect on lemon fruit production due to lack of water as excess irrigation in W5 treatment due to nutrient leaching. The fruit yield of treatments W2S1 (15.3 kg per tree) and W5S2 (15.8 kg per tree) was the same. The low yield of W2S1 treatment was due to lack of water while the low yield for treatment W5S2 was due to high salinity and nutrient leaching. The same trend was at W2S2 and W5S3 treatments. Although crop water use (Etc) was the same at treatments W3S1 and W4S3, fruit yield in W4S3 significantly reduced by about 56% as compared to W3S1 treatment due to high salinity. Irrigation water salinity is very important factor that should be managed with limited (deficit) irrigation. Also, increasing amount of applied saline water could result in a negative effect on crop yield and environment such as increasing average root zone salinity, nutrient leaching, water logging, increasing the drainage water load of salinity which might pollute ground water and other water sources.
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4. Conclusions Increasing irrigation water salinity increased salt concentration and osmotic potential in the root zone and consequently reduced lemon annual water use, stem diameter and fruits yield. The percentage shaded area significantly increased with time being 1.11, 2.89, 5.17, 15.8 and 22.34% in the first, second, third, fourth and the fifth years, respectively. The first 3 years were devoted for adaptation and root development, and the significant vegetative growth started with the fourth year and consequently water requirement. The significant increase in stem diameter was in the first two years being about 3±4 times higher than that at planting, and continued to increase but in a decreasing increment for the following years. Lemon fruits were harvested for the first time about 44 months from planting date. Without supplemental irrigation, lemon trees cannot survive the first year even with a total rainfall of 274 mm. Regardless of irrigation water salinity, the significantly highest fruit yield was at irrigation water depth equal to evaporation depth from class A pan when corrected for tree canopy percentage shaded area. Acknowledgements This research was sponsored by the Deanship of Scientific Research at the University of Jordan, Amman, Jordan. References Abu-Awwad, A.M., Hill, R.W., 1990. Tomato production and soil salt distribution under line-source trickle irrigation. J. Agronomy Crop Sci. 167, 188±195. Ayers, R.S., Westcot, D.W., 1985. Water quality for agriculture. Irrig. Drain. Paper no. 29, Rev. 1. FAO, Rome, Italy. Bielorai, H., Shalhevet, J., Levy, Y., 1978. Grapefruit response to variable salinity in irrigation water and soil. Irrig. Sci. 1, 61±70. Cerda, A., Nieves, M., Guillen, M.G., 1990. Salt tolerance of lemon trees. Irrig. Sci. 11, 245±249. Cole, P.J., McLeod, P.I., 1985. Salinity and climatic effects on the yield of citrus. Aust. J. Exp. Agric. 25, 711± 721. Chartzoulakis, K., Michelakis, N., Stefanoudaki, E., 1999. Water use, growth, yield and fruit quality of Bonanza oranges under different soil water regimes. Adv. Hort. Sci. 13, 6±11. Doorenbos, J., Kassam, H.A., 1979. Yield response to water. Irrig. Drain. Paper no. 33. FAO, Rome, Italy. Ghassemi, F., Jakeman A.J., Nix, H.A., 1995. Salinization of Land and Water Resources. University of New South Wales Press, Sydney, Australia, 526 pp. Green, G.C., Moreshet, S., 1979. An analysis of seasonal water use characteristics of Valencia orange trees in the Sundays River Valley. Crop Prod. VIII, 179±183. Keller, J., Bliesner, D.R., 1990. Sprinkler and Trickle Irrigation. Van Nostrand-Reinhold, New York. Levy, Y., Shalhevet, J., 1990. Ranking the salt tolerance of citrus rootstocks by juice analysis. Scientia Hort. 45, 89±98. Marschner, H., 1997. Mineral Nutrition of Higher Plants, 2nd Edition. Academic Press, 24±28 Oval Road, London NW1 7DX. Mass, E.V., 1986. Salt tolerance of plants. Appl. Agric. Res. 1, 12±26. Mass, E.V., 1993. Salinity and citrus culture. Tree Physio. 12, 195±216.
A.M. Abu-Awwad / Agricultural Water Management 52 (2001) 53±71
71
Mass, E.V., Hoffman, G.J., 1977. Crop salt tolerance-current assessment. Proc. W. Soc. Civ. Eng.: J. Irrig. Drain. Div. 103 (TR2), 115±134. Ministry of Agriculture, 1998. Annual Report. Amman, Jordan, 108 pp. Nastou, A., Chartzoulakis, K., Therios, I., Bosabalidis, A., 1999. Leaf anatomical response, ion content and CO2 assimilation in three lemon cultivas under NaCl salinity. Adv. Hort. Sci. 13, 61±67. Shalhevet, J., 1994. Using water of marginal quality for crop production: major issues. Agric. Water Manage. 25, 233±269. Shalhevet, J., Yaron, D., Horowitz, M., 1974. Salinity and citrus yield. An analysis of results from a salinity survey. J. Hort. Sci. 49, 15±27.