POSSIBILITY OF WATERTABLE MANAGEMENT THROUGH SUB-IRRIGATION IN EGYPT

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1 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt 973 POSSIBILITY OF WATERTABLE MANAGEMENT THROUGH SUB-IRRIGATION IN EGYPT E. Abdel Ghaffer 1, and M.A.S. Wahba 2 1 Head of Climate Change Department, Environment and Climate Research Institute, National Water Research Center, Delta Barrage (El-Kanater) Cairo, Egypt P.O. 3621/5, Phone: 20(2) , Fax: 20(2) , Dr_eman30@hotmail.com. 2 Senior Researcher, Drainage Research Institute, Egypt ABSTRACT At the beginning of the twenty-one century, the world and especially the developing countries are facing the challenges of securing water and food for an expanding population. These challenges necessitate developing new management strategies to conserve and use the existing water resources more efficiently. Sub-irrigation is one of these management strategies, in which water is supplied through the subsurface drainage system using control structures to regulate the water table level in the field. Some existing subsurface drainage systems may be retrofitted for sub-irrigation that called dual-purpose drainage / sub-irrigation systems. This system has many benefits as it satisfies both drainage and irrigation needs at lower initial costs; needs less energy, conserves rainfall in better way depending on management strategy; offers more flexibility in managing drainage water; improve quality of drainage water and reduces evaporation during irrigation time. The overall objective of this study is to detect the possibility of applying sub-irrigation in Egypt and to determine the effect of drainage water reused in combination with sub-irrigation technique on water table and soil salinity and crop yield. The study was carried out in Maruit Experimental Station (MES), south of Alexandria City in the western delta, which served by subsurface drainage system. In MES, the main source of the irrigation water is supplied from the mixed drainage water by Maruit pumping station with fresh water taking from Nubaria main canal. Two techniques were applied in MES, the first technique was surface irrigation with free drainage and the second one was sub-irrigation technique. The monitored media were water table depth, rainfall, water and soil salinity and crop yield. The study revealed that the intensive management is a very important aspect for the success of sub-irrigation technique and wheat crop yield was higher by 15% with sub-irrigation treatment compared to surface irrigation treatment. Keywords: Sub-irrigation, controlled drainage, subsurface drainage, watertable management, watertable salinity, treatments, Soil salinity and crop yield.

2 974 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt INTRODUCTION Water table management is the regulation of soil-water excess and availability by structures specially designed for given farm site conditions. Water table management consists of three basic practices (Figure1). These are conventional subsurface drainage, controlled drainage, and sub-irrigation. Farm lands susceptible to seasonal or intermittent high water tables usually require subsurface drains which serve to lower the water table to a level equal to the drain depth (Figure 1-a). Subsurface drains or land drainage plays an important role in the maintaining and improving crop yields as it prevents a decrease in the productivity of arable land due to rising water tables and the accumulation of salts in the root-zone, ICID [10]. The addition of control structures to a subsurface drainage system (controlled drainage) allows the drainage outlet to be set at any level between the ground surface and the drains. Raising the outlet after planting helps keep water available for plant use (Figure 1-b). Abbott et al. [1] reported that the main benefits of controlled drainage in irrigated agricultural areas are as follows: Increasing the water use efficiency. Improving the crop yields and Reducing the nitrate and phosphate losses to downstream water bodies, besides reducing eutrophication and ecological damages. With sub-irrigation, one system provides the drainage and irrigation requirements for the crop. Water is supplied through the subsurface drainage system using control structures to regulate the water table level in the field. Irrigation water is applied below the ground surface, thus raising the water table to the crop root zone. Sub-irrigation practice can be used to create a constant water table depth (Figure 1-c). Sub-irrigation systems require a high level of management to avoid excess soil wetness following rainfall (Larry et al. [11]). Abdel Ghaffer and Ragab [3] reported that with sub-irrigation, the soil moisture content of lower layer ( m) was higher than that of surface layer (0-0.3 m). The objective of this research is to detect the possibility of applying sub-irrigation in Egypt. Moreover, to determine the effect of water reused in combination with subirrigation technique on the salinity of water table and soil in addition to the crop yield. Site requirements for sub-irrigation Sub-irrigation system will likely be the most effective and economical alternative on sites that satisfy the following requirements (Evans and Skaggs [8]):

3 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt Improved drainage (at least in its natural state). 2. Relatively flat surface slope of less than 1 percent. 3. Moderate to high hydraulic conductivity. 4. High natural water table. 5. An adequate available water supply to be used during the driest parts of the growing season. a b c Figure (1) Three Water Table Management Practices: a) Conventional Subsurface Drainage, b) Controlled Drainage, and c) Sub-irrigation After Ohio State University [13] METHODOLOGY Experimental site Experiment was conducted at Maruit Experimental Station (MES) in an area of 10 feddan. MES is located south of Alexandria City in the western delta and has a sandy silt loam to clay loam texture, Abbott et al. [2]. The field hydraulic conductivity was measured using the auger hole method and the average value is 2.0 m/day. The

4 976 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt main source of the irrigation water for (MES) is supplied from the mixed drainage water by Maruit pumping station with fresh water taking from Nubaria main canal. MES has a surface irrigation system, which consisted of one main canal and six subcanals (plain concrete rectangle section). Irrigation water was supplied through the surface irrigation canal. The water is distributed between the plots by opening the gate at the entrance of one plot and closing the gates of other plots as Figure (2). MES is served by a subsurface drainage system that was installed in May The collector drains (PVC corrugated plastic pipe) have been installed at about 1.5 m depth and all laterals drains (PVC corrugated plastic pipe covered by synthetic envelope materials) have been installed at a depth of 1.2 m with an average space of 32 m. The lateral drains were sloped at 10% and exit directly to the main collector through a manhole. Treatment factor Two water table management treatments were applied in MES, conventional free drainage of drains 1.2 m deep with surface irrigation (SI) treatment and sub surface irrigation treatment (SSI) at a design water table depth at 0.6 m (British Columbia [4]). Subsurface drainage / sub-irrigation operation and management Irrigation water is applied to (SSI) treatment from the sub-canal to the first (inlet) manhole at the beginning of the PVC collector of the subsurface drainage system, Figure (3), then flowed to all laterals (field drains) and upward to root zone by capillary flow. The outlet of the collector has a control device (gate) to maintain the water table at depth of 0.6 m under the soil surface (Figure 4). The water table depth was monitored daily in the observation wells, and irrigation water was added when the water depth was deeper than 60cm. In the occurrence of rainfall and shallower water table depth, free drainage was applied.

5 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt 977 Figure (2) Layout of Maruit Experimental Station

6 978 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt Figure (3) Sub-irrigation Path Measurements The field measurements were carried out for the winter season of and the measurements included water table depth, irrigation and water table salinity, rainfall and soil salinity. Irrigation water salinity It was measured before each irrigation gift by a handheld electrical conductivity meter in deci Siemens per meter (ds/m). Water table depth It was measured daily in a set of 64 observation wells that installed and distributed in three rows along the lateral length (¼ L, ½ L and ¾ L) in the experimental field for both treatments. A sounder and a tap measured the water table depth. Average water table depth was calculated for the observations wells that installed above laterals in (SSI) treatment while it was calculated for the observations wells that installed between laterals in (SI) treatment.

7 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt 979 Figure (4) Controlled Gate for Sub-irrigation Technique Water table salinity The water table salinity or the electrical water conductivity was measured for both treatments two times a weak by an Ec apparatus in ds/m unit, for detecting the effect of sub-irrigation technique on water table salinity. Rainfall It was recorded in case of its occurrence using the manual rain gauge in the experimental field. Soil salinity Soil samples were taken from both treatments (SI and SSI) each two weeks to a depth of 0.6 m at an interval of 0.15 m for chemical analysis to follow up any change in its salinity. In addition to, fifty soil samples that were taken before cultivation for the determination of the initial salinity. The soil salinity was determined in the laboratory of Drainage Research Institute. Crop yield Observation of wheat growth was followed and four crop samples were taken from each treatment at harvest time to determine the average wheat crop yield. Locations crop samples are illustrated in Figure (2).

8 980 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt RESULTS AND DISCUSSION Water table depth The average water table depth and rainfall for both treatments (SI) and (SSI) along the winter season ( ) are represented in Figure (5). In the rainfall period, the water table depth has peak values with shallower depth. The statistical analysis shows that the average water table in SSI treatment reaches the design depth (60 cm) in 40 % of the measures and this due to the existence of rainfall and some seepage from the control device. Moreover, subsurface irrigation technique was applied for the first time and more experience and training for the water table manager is required. Figure (5) Average Water Table Depth (m) for Surface Irrigation (SI) and Subsurface Irrigation (SSI) Treatments Water table salinity The water table salinity for both treatments was represented in Figure (6). It ranges from 4.57 to 6.37 ds/m with an average value of 5.28 ds/m for SI treatment while the water table salinity for SSI treatment ranges from 4.2 to 6.25 ds/m with an average value of 5.25 ds/m. It is obvious from these results that there is no difference between the water table salinity for both treatments and these results were confirmed with the result of the statistical analysis of the T-Test which improved that there is no significant difference between the salinity of the water table for both treatments (SI and SSI) at (P = 0.36). In general the water table had high salinity degree and this due to the high irrigation salinity that had an average value of 4.87 ds/m.

9 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt Water Table Salinity (ds/m) Water Table Salinity(SSI) Water Table Salinity(SI) 14/12/ /12/ /03/04 01/10/04 20/1/ /1/ /10/04 17/2/ /2/ /3/ /3/2004 Date Figure (6) Water Table Salinity for Surface Irrigation (SI) and Subsurface Irrigation (SSI) Treatments Soil salinity Figure (7) shows the average soil salinity for both treatments (SI and SSI) along the soil depth, The figure shows that the pattern of soil salinity for SSI treatment started with high value of 3.11 ds/m at the upper layer and decreases with depth to a value of 2.57 ds/m and this result is confirmed with the logical, where the irrigation water passes through the subsurface drainage system upward by capillary flow, and the opposite is true concerning SI treatment where the low value of 2.35 ds/m at surface layer and increases to a value of 2.6 ds/m with depth as the salt transported to the lower layer due to leaching process. The soil salinity for SSI treatment is higher than that of SI treatment, but its value was still less than the threshold of wheat cultivation of 6 ds/m, FAO [9] and DWIP [6]. Moreover, the value of irrigation water salinity ranged from 4 to 6.4 ds/m with average value of 4.87 ds/m because the irrigation water is a mixture between fresh water and agricultural drainage water. The statistical analysis using the Mann - Whitney U Test shows that there is significant difference between the soil salinity of the two treatments SI and SSI at (P = 0.014). Crop yield Figure (8) shows the average Sakha 8 wheat yield for both sub-surface irrigation (SSI) and surface irrigation (SI) treatments. In case of (SSI) treatment, the wheat yield was ardab/fed.; this exceeds the yield of surface irrigation treatment (SI) by 15%. This result strongly related to the finding of Abdel Ghaffer and Ragab [3], they reported that with sub-irrigation, the soil moisture content had not lower value than that with surface irrigation and free drainage. However, the soil salinity for SSI treatment is higher than that of SI treatment, but its value was still less than the threshold of wheat cultivation of 6 ds/m, FAO [9] and DWIP [6]. By reviewing the wheat crop yield (Sakha 8) for Alexandria Governorate, it was 13.7 ardab/fed. for year

10 982 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt 1999, Statistical agriculture [13]. Moreover, the wheat yields using low water (Ecie = 2.15 ds/m) and soil salinity (Ecie = 5.11 ds/m) in west of delta for year 1995 equal ardab/fed. and the average Sakha wheat yield in the west of Delta (El- Mahmoudia district) was ardab/fed. for 1996 season, DWIP [6]. Generally, more than factor affected the wheat crop yield. The main factor is the application of adequate amounts of water at the proper growth stage to obtain potential crop yield of wheat. Brown et al. [5] and Evans et al. [7] reported that higher yield with sub-irrigation could be achieved with more aggressive use of sub-irrigation (i.e. higher design water table depth). Average Soil Salinity (ds/m) SI 10 SSI 20 Depth (cm) Figure (7) Average Soil Salinity for Surface Irrigation (SI) and Subsurface Irrigation (SSI) Treatments Acverage Wheat Yeild (Ardab / Fed SSI (Subirrigation ) Wheat Yeild (Shakha 8 ) SI (Surface Irrigation) Figure (8) Crop Yield for Surface and Subsurface Irrigation Treatments

11 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt 983 CONCLUSIONS Intensive monitoring and management is necessary for effective operation of dualpurpose drainage /sub-irrigation system. The sub-irrigation technique did not increase the water table salinity as there was no significant difference between the water table salinity for both treatments at P = The combination of sub-irrigation technique with reused water hadn t affect water table salinity, soil salinity and wheat crop yield. The wheat grains yield in case of sub-irrigation treatment (Sakha 8) was greater than that of surface irrigation by 15% and equal to ardab/fed. RECOMMENDATIONS The long-term effect of sub-irrigation with reused water on water table salinity, soil salinity and crop yield should be studied. The long-term impacts of sub-irrigation technique should be applied and tested under different field conditions with respect to soil type, crop, and weather. The drainage water quality should be studied under sub-irrigation technique. REFERENCES 1. Abbott, C.L, AL.o Cascio, S. Abdel-Gawad, J. Morris and T. Hess, Guidelines for Controlled Drainage. HR Wallingford, Drainage Research Institute and DFID Department for International Development, Technical Report OD 147, Abbott, C.L., Abdel-Gawad, S., Wahba, M.S., and L. o Cascio, Field Testing of Controlled Drainage, and Verification of the Wasim Simulation Model. HR Wallingford Technical Report OD/TN 102, Wallingford, Oxon. OX108 BA, UK, Abdel Ghaffer, E. and M.A.M. Ragab. Potential Impact of Sub-Irrigation on Soil Properties in West Delta.Q.52 P.1.02, International Congress on Irrigation and Drainage, Nineteenth Congress, Beijing British Columbia, Controlled Drainage /Sub-irrigation. Drainage Fact Sheet. Order No British Columbia, Ministry of Agricultural and Food, Brown, L.C., A. Ward, and N.R. Fausey, Water Table Management Systems. Available at: DWIP, Final Report on Drainage Water Irrigation Project. Drainage Research Institute and Louis Berger International, Inc. and Pacer Consultants, 1997.

12 984 Tenth International Water Technology Conference, IWTC , Alexandria, Egypt 7. Evans, R.O., J.W. Gilliam, and R.W. Skaggs, Controlled drainage management guidelines for improving drainage water quality. Publ. AG-443. Raleigh, N.C: North Carolina Cooperative Extension Service, Evans, R.O. and R.W. Skaggs, Agricultural water management for coastal plain soils. North Carolina Cooperative Extension Service. Publication Number AG 335, FAO, The use of Saline Water for Crop Production; Irrigation and Drainage Paper 48, ICID, Amendments to the constitutions, Agenda of the International Council Meeting at Rabat. International Commission on Irrigation and Drainage, Morocco. ICID, New Delhi, pp. A , Larry C. Brown, Andy Ward, and Norman R. Fausey, Water Table Management Systems. Department of food agricultural and Biological Engineering. The Ohio State University and USDA-ARS Soil Drainage Research Unit Columbus, Ohio-State University. Agricultural Drainage, Bulletin 871 USA, Statistical agriculture, Economic Sector affair. Agriculture and reclaiming lands, 1999.