REDUCING SOIL SALINITY AND IMPROVING CROP YIELD IN SALINE HEAVY CLAY USING A FILLED TECHNIQUE

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1 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt 113 REDUCING SOIL SALINITY AND IMPROVING CROP YIELD IN SALINE HEAVY CLAY USING A FILLED TECHNIQUE Yasser Ahmed Hamed Civil Engineering Department, Faculty of Engineering, Suez Canal University Port Fouad - Port Said, Egypt Yasser_ham@hotmail.com ABSTRACT Soil salinity is a major cause for reducing the quality and quantity of crop yield. The objective of this paper is to investigate the effect of a new technique using filled drains with organic materials and soil together with open drains to reduce soil salinity and increase crop productivity in heavy clay soil. Two plots 35 x 1 m were chosen, one with a filled drain in the centre of the plot and the other without. Bulk soil salinity measurements were taken by the WET sensor. The salinity maps show that there is a significant decrease in soil salinity all over the plot with the filled drain while the decrease was not significant at the other strip. The results also show an increase in quantity and quality of the crop yield at the filled drain strip. Keywords: Soil salinity Drainage WET sensor Clay soil Egypt 1. INTRODUCTION FAO (19) referred that the major problem for Egyptian soils is the increasing soil salinity. It was stated that a decline of 3% of the soil productivity is attributed to this unfavourable process. High salt contents in soil decrease the osmotic pressure and cause water to flow out of the plant to achieve equilibrium. Less water can thus be absorbed by the plant and this causes stunted growth and reduced yield. Too high salt contents may also cause leaf tip and marginal leaf burn, bleaching, and/or defoliation (Perfetti and Terrel, 199). The natural concentration of salt is largely influenced by the geologic formation underlying the area (James and Evison, 1979). Low salinity is expected in non-faulted areas underlain by igneous geologic formations (Perfetti and Terrel, 199). High levels of dissolved solids often occur in areas underlain by ancient marine sediments. Salt concentration is expected to be high in arid and semiarid areas where evaporation usually exceeds precipitation. However, high salt concentration may also be found in semi-humid areas. As water evaporates from existing water bodies, salt concentrations increase. Because precipitation itself contains minute traces of salt, evaporation after a rain leaves salt in the soil. This salt may be carried in irrigation return flow or in overland flow during the irregular rains (Perfetti and Terrel, 199).

2 11 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Leaching is a process of displacing soil solution by incoming irrigation water and thus is strongly dependent on the soil water-holding capacity. This can clearly be shown for rainfall leaching as the same amount of rainfall will displace the pore volume of a sandy soil having a low water holding capacity by a greater factor than of a soil having a high water-holding capacity, resulting in a more thorough removal of accumulated salts (Shalhevet, 199). Leaching interacts closely with crop growth, irrigation methods, and soil-physical properties. The net downward movement of water and salt controls salt accumulation in the soil generates drainage water, and influences drainage requirements and drainage water quality. The greater the salinity of the irrigation water, the greater the leaching, or drainage, required to maintain salinity in the soil at levels which are not toxic to crops (Oster, 199). The area which suffers from primary or secondary salinity in Egypt was estimated to be about, ha representing approximately one-third of the entire area of the arable land in the country. The introduction of perennial irrigation without complementary drainage has great influence on the progress of salinization. Under the present system of intensive perennial irrigation, groundwater levels in many areas no longer recede seasonally, but remain at high levels throughout the year, and many areas have concentrated salts in the root zone to levels that significantly reduce the crop production (Younes et al., 1993). A major irrigation project, the El-Salam Canal project, was planned for the re-use of wastewater and drainage water from two main drains in the Eastern Delta. This water, added to water extracted from the Damietta branch of the Nile, is used for irrigation of a new area of, Feddan in North Sinai and, Feddan west of Suez Canal. However, many of the service areas of this project are suffering from high level of soil salinity. The area located west of Suez Canal is characterized by heavy clay soil and saline groundwater table (3 ds/m) at depth cm. Water flow to the surface from the water table by capillary rise and evaporate leaving salt behind causing the increase of soil salinity. Hamed et al. (7) investigated the effect of spatial soil salinity distribution and land alignment on two crops grown on heavy clay soil in a site adjacent to our study area. They used the same methodology and the same device for measuring bulk soil salinity (the WET sensor). They concluded that one of the important causes of the high soil salinity at this area is the shallow saline (3 ds/m) groundwater table located. 1 m from the surface. They suggested that management of the area has to be improved not to increase salinity hazards or to decrease crop yield significantly. An obvious and simple measure is to increase the number of open drainage channels. However, this will reduce the cultivated area. So, they recommended that in order to keep the cultivated area, sub-surface drain pipes may be required. Since sub-surface drain pipes will be very expensive, the need for an effective and cheap equivalent method is crucial. The purpose of this study is to investigate a new technique for reducing soil salinity and improving crops yield (quantity and quality) in a heavy clay soil by using a filled

3 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt 115 ditch together with open drainage channels. To this end measurements of bulk electrical conductivity was taken several times during one year at two fields, one with a central filled ditch and one without, to study temporal and spatial variation. Crop quality and quantity was also monitored during the same period.. MATERIAL AND METHODS.1 Area description Two strips 35 m x 1 m were chosen at a site located west of Suez Canal, 1 km south of Port-Said city Egypt (Fig. 1). The two strips are m apart. Strip has a filled ditch at its center while strip 1 is an ordinary strip. The dimensions of the filled ditch are the same as the open ones at the two edges of the strip. A filled ditch is an old open ditch filled with residues of grass and trees and original soil. The mixture of the soil and the organic material was manually prepared carefully outside first (organic materials 3 %) and impeded into the ditch on layers. Each layer thickness is 5 cm in order to keep the mixture homogeneity for all the ditch volume. The site is located within the El-Salam Canal project service area. The field site has been used for agriculture before constructing this technique for one year but with very poor yield. The soil is heavy clay. Soil properties for the two strips are described in Tables 1 and. Table (1) Soil properties for strip (1) Depth ( cm ) Clay (%) Silt (%) Fine sand (%) Bulk density (kg/m 3 ) Table () Soil properties for strip () (with filled ditch) Depth ( cm ) Clay (%) Silt (%) Fine sand (%) Bulk density (kg/m 3 ) The material in the filled ditch consists of -7 % heavy clay soil which has the same properties as soil for strip and 3- % organic material (grass and wood residue). The annual precipitation for the area is 75 mm and the mean potential evaporation per

4 11 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt day is 3.3 mm. The land was covered by saline lake water until years ago. The samples locations are shown in Fig. (). Cultivation depth (tillage depth) at both strips is -3 cm. Below this depth the soil is little evolved and characterized by prismatic clay structure with some cracks. These cracks are formed by shrinkage resulting from desiccation of the clay.. Measurements of the bulk soil salinity Measurements of the bulk soil salinity were made three times per month during one year from the beginning of May 5 to the end of April 5 in the two strips. Three crops have been cultivated at this period (Maize, Rice and Clover). In every strip twenty measurement points were chosen through a grid 3x1 m with intervals 1 and.5 m between points (Fig. ). Three readings were taken by the WET Probe (Delta-T Devices) in every point at depths 1,, and 3 cm from the soil surface. The readings were taken at the same points three times per month four days after irrigation. Irrigation water salinity was measured every time. Soil samples were also collected at depths 1, 1,, and 5 cm at four points located at the middle of each side of each strip. Soil samples were sent to the laboratory and analyzed to determine the soil properties (Tables 1 and ) Contour maps of the bulk soil salinity for both of the sites and for all depths were drawn by using Surfer software (Golden Software Inc. Colorado, USA)..3 Analyzing Crop Yield Quantity and Quality Photos for each strip were taken by a digital Camera one week before a Clover yield was harvested. Photos were analyzed using Adobe Photoshop CS. The ratio of the green area was calculated in each strip in order to calculate the ratio of vegetation and consequently the quantity of the yield in each strip. At the same time, four representative vegetation samples were taken from the filled ditch strip (strip ) and one representative vegetation sample was taken from strip 1 in order to analyze the crop yield quality.

5 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt 117 Field site Fig. 1. Location of the field site

6 11 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Minor Drain Ditch 1 m Filled Ditch Ditch 35m Field Canal North Measurement point Fig.. The layout of the strips; the filled ditch is only at strip (). Theoretical Considerations The WET sensor measures the dielectric properties of soils, and gives the water content, electrical conductivity, and temperature. The sensor consists of a probe that is inserted in the soil, and a handheld logging unit, HH Moisture Meter. When the WET sensor is inserted into the soil and takes a reading it generates a MHz signal which is applied to the central rod and produces a small electromagnetic field within the soil. The water content, electrical conductivity and composition of the soil surrounding the rods determines its dielectric properties. The WET sensor detects dielectric properties from changes relative to the MHz signal, and sends the information to the HH. The sensor measures the capacitance (C) and conductance (G) of the material surrounding the probe. These values can be translated to conductivity EC b (bulk soil electrical conductivity) and permittivity b (which represents the dielectric properties)

7 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt 119 using calibration tables that is preinstalled in the HH. The temperature is measured by a small sensor in the tip of the central rod. The EC b and b are used in the calculations of (water content) and EC p (pore water electrical conductivity) using the following formulas (Hilhorst, ): ε < ' b ε ε ε > ε ' b ' b water water EC EC EC p p p EC ε = ε SP b ' b b ' b = EC b water EC ε = ε SP water ' ε b ε 3 water (1) () (3) where water =.3.( T ), T = temperature, and SP is a soil parameter that can be calculated from a calibration experiment (see Hamed et al. 7). The subscript s denotes readings in soil and w in water. In the previous study, Hamed et al. (7) and during the field study it became apparent that the extremely high EC b of the saline clays affected the permittivity, resulting in very high values of ' b. This makes the sensor indicate a water observation, and no real calculation of EC p is made. Due to this problem all evaluations in this paper were based on the measured EC b -values. We repeat the same procedure in the current paper. 3. RESULTS AND DISCCUSION 3.1 Hydrological Impacts Figure 3 shows a schematic diagram showing the difference of water table levels between the two strips. In strip 1, as the result of long distance between the ditches (1 m), the water table is gradually approaching the surface and became very close to the surface at the centre. Consequently, soil salinity gradually increases as a result of flowing upward of saline water from the water table by capillary rise. In case of existence of a filled ditch at the middle of the two ditches, the hydrology of the strip will be changed (as shown from Fig. 3). The groundwater will be lowered and hence soil salinity will be decreased especially at the middle distance of the strip (filled ditch location) which will have the minimum groundwater level.

8 117 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Open ditch 1 m Open ditch 1.m Max water table level Strip 1. m. m Open ditch Filled ditch Open ditch 1.m Max water table level Strip Fig. 3. Schematic diagram showing the difference of water table levels between the two strips 3. Soil Salinity The change in flow patterns in the unsaturated and saturated soil described above also had affects on the salinity distribution of the two plots. Figures - show the contour maps of the bulk soil salinity for 1,, and 3 cm depths for both of the strips for initial condition, 3,, 9, and s period. For strip, the salinity range for depth 1 cm decreased from.9 1. ds/m to ds/m. For depth cm, the soil salinity range decreased from ds/m to. -.7 ds/m and finally for depth 3 cm the salinity decreased from ds/m to.5-.7 ds/m. For strip 1, the salinity range for depth 1 cm decreased from..9 ds/m to.7.9 ds/m. For depth cm, the soil salinity range decreased from -9.5 ds/m to 3.. ds/m and finally for depth 3 cm, from. 1. ds/m to ds/m. The salinity range of the irrigation water is ds/m. From the graph, soil salinity decreases significantly close to the filled ditch for the three depths for strip. This decrease is directly linked to the increased drainage through the more permeable soil in the filled ditch. The decrease in soil salinity spread also all over the strip area. It is probably due to the overall lowering of the saline groundwater table as a result of using a filled ditch between the two open ditches. Lowering of the groundwater table will decrease the amount of saline water flow upwards to the surface by capillary rise which will evaporate and leave the salt at the surface.

9 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Strip 1 Strip Fig.. Bulk soil salinity distribution for both of the strips for 1 cm depth (initial condition, 3,, 9 and period

10 117 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Fig. 5. Bulk soil salinity distribution for both of the strips for cm depth (initial condition, 3,, 9 and period

11 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Fig.. Bulk soil salinity distribution for both of the strips for 3 cm depth (initial condition, 3,, 9 and period

12 117 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Strip 1 also displays a decrease in salinity due to the irrigation for all depths. However, the decrease is less significant compared to strip. From the salinity maps you can also see that the salinity distribution is more random and does not change much over time. Figure 7 shows a comparison between the mean cross sections between strip 1 and strip for different depths (1,, and 3 cm) and for different time (initial condition, 3,, 9, and ). For strip and for all the depths, the bulk soil salinity decreased significantly with time at the filled ditch location (centre of the strip) and more uniformly for the remaining strip area. Consequently, it will help leaching salt by continuous irrigation with relatively low salinity irrigation water. On the other hand, for strip 1, the decrease of soil salinity is less significant for depths 1 and cm and is scattered for depth 3 cm. For all depths the general pattern is that the salinity is highest in the centre of the strip where the groundwater table is closest to the soil surface. Figure shows a comparison between strip 1 and strip for a longitudinal section along the middle of the strip (located at the centre of the filled ditch for strip ()). Again, the bulk soils salinity decreased significantly and uniformly at the area along the filled ditch (strip ) for all the depths. On the other side, the soil salinity distribution by time is relatively random for strip Yield Quantity Photos 1 and show a comparison between the vegetation for Clover crop (yield quantity) between the two strips. For strip (down), the photo shows that more than % of vegetation located mainly at the area along the filled ditch. It is probably due to the decrease in soil salinity along the filled ditch. Moreover, the organic material at the filled ditch (grass and trees residues) may act like fertilizers to the soil at this area contributing for improving the crop yield. While photo shows that strip 1 is barely vegetated (less than 1%), vegetation occurs only along the edges adjacent to the ditches and the drain. It is probably due to the high soil salinity along strip and the leaching of salt in areas near the ditches and drain which contribute for decreasing soil salinity and improving yields in these areas. The same trends of results were obtained for the other two crops (Maize and Rice).

13 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Depth (1cm) (strip ()) 1 1 Depth 1 cm (strip(1)) Depth (cm) (strip ()) Depth cm (strip(1)) Depth (m) Depth (3 cm) (strip()) Depth 3 cm (strip(1)) Fig. 7. Comparison between the mean cross sections between strip (1) and strip () for different depths (1, and 3 cm) and for different time (3,,9 and )

14 117 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Depth 1cm (strip()) initial condition s s s s Depth 1 cm (strip(1)) Depth cm (strip()) 1 Depth cm (strip(1)) Depth 3 cm (strip()) Depth 3 cm strip (1) Fig.. Comparison between strip (1) and strip () for a longitudinal section along the middle of the strip (located at the centre of the filled ditch for strip ())

15 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Yield Quality Figure 9 shows a comparison of yield quality (for clover yield) between the two strips. For strip 1 there is almost no vegetation but only small with worst quality (B) for areas adjacent to the ditches. For strip (with filled ditch), the quality of vegetation is highly improved. The highest quality (A) was found at area located at the filled ditch. It is probably due to the decrease in soil salinity and the existence of organic material at the filled ditch which may act like fertilizes. The quality of the crop is decreased gradually (C and B) away from the filled ditch and vegetation vanishes at.5 m away from the centre of the filled ditch. It is probably due to the increase in soil that salinity vanishes away from the ditch. Near the open ditch on the other side, the vegetation is increased with good quality (D). It is probably due to the decrease in soil salinity along the strip and the leaching of salt to the near opened ditch. The same trends of results were obtained for the other two crops (Maize and Rice).. SUMMARY AND CONCLUSION A new technique of using filled ditches instead of open was investigated in terms of its effect on decreasing soil salinity and improving yield quantity and quality in heavy clay soil. A strip 35 x 1 m with a filled ditch at its centre was compared with a strip with the same dimensions without filled ditch. The strips are surrounded by opened drains and two ditches from three sides and a field canal with the fourth side. Twenty measurement points were chosen for each strip. Bulk soil salinity measurements were recorded at every point at three depths 1,, and 3 cm from the soil surface. Both of the salinity maps and the cross sections and longitudinal sections maps showed that soil salinity have decreased significantly along and near the area of the filled ditch. Moreover, the decrease of soil salinity also spread along the strip area with filled ditch. The reason is the leaching of salts at the area of the filled ditch. Moreover, the existence of the filled ditch altering the saline ground water level and decrease it. Consequently, the saline water which was flow upward by capillary rise was decreased and contributes for decreasing soil salinity all over the strip. On the other hand, the high salinity level at the strip without the filled ditch was only decreased as a result of washing by irrigation water which is not enough since the risk of saline water which moves upward from the shallow groundwater was still exist. The distance between the opened ditches is the strip width (1 m) which contributes for shallow saline ground water at the middle area of the strip. Photos of the crop yield (Clover) shows that the vegetation (crop quantity) at the filled ditch strip was more than the vegetation at the ordinary strip by at least times. The quality of the filled ditch strip is much more than the quality of the ordinary strip especially at the area along the filled ditch. The improve of quantity and quality of the crop yields is probably due to the decrease in soil salinity and the existence of organic materials (3-%) at the filled ditch which may act like fertilizes.

16 117 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt A B C D 1., A C B no-vegetation D Cross section in Strip () m.5 B no-vegetation B Cross section in Strip (1) Fig. 9. Comparison of yield quality between strip (1) and strip ()

17 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt 1179 The crop yield quantity and quality was monitored one year after the experiment for a series of crops (Maize, Rice and Clover) and the same results were recorded. The study proved that the technique of using filled ditch of organic material mixed with the original soil in between open drainage channels was useful and effective for reducing soil salinity and improving the crop yield quantity and quality. Since the vegetation is poor in areas between the filled ditch and the opened one, it is recommended to use another filled ditches in between. The current spacing is 5 m between the filled ditch and the opened one which will be.5 m if another filled ditch was used in between. It is expected that the crop quantity and quality will be improved by adding new filled ditches. However, it is recommended to continue conducting studies and investigation for the new methodology. Studies should also continue in order to investigate sustainability which is considered a corner stone for the new technique. For two years (one year of experiment and one for monitoring crop yields) the technique was approved its success. At the end of our experiment, the farmer started to use this technique in new reclamation area which has given satisfactory results up till now. Acknowledgements The field work was financially supported by the Swedish Research Council (SIDA). The analysis of the data was funded through a scholarship to the author from the Swedish Institute. Special thank to Prof. Ronny Berndtsson, Dr. Magnus Persson and Dr. Mohamed El-Kiki, for their help. REFERENCES Dalton, F.N., Herkelrath, W.N., Rawlins, D.S. and Rhoades, J.D., 19. Time-Domain Reflectometry: Simultaneous Measurements of Soil Water Content and Electrical Conductivity with a Single Probe. Science, FAO, 19. The Land Resource Base. Rome : FAO (ARC//3). Hilhorst, M.A.,. A pore water conductivity sensor. Soil Science Society of America Journal,, Hamed, Y. and Berndtsson, R., 7. Effect of land alignment and spatial soil salinity distribution on Clover and Sugar beet yield. Archives of Agronomy and Soil Science 53(), James, A. and Evison, L., Biological Indicators of Water Quality. John Wiley and Sons, Ltd., NY. Oster, J.D., 199. Irrigation with poor quality water. Review article, Agric. Water Mgmt., Vol. 5,

18 11 Twelfth International Water Technology Conference, IWTC1, Alexandria, Egypt Perfetti, P.B., and Terrel, C.R., 199. Water Quality Indicators Guide: Surface Waters. USDA Misc. Publ. SCS-TP-11. U.S. Gov. Print. Office, Washington, D.C. Roth, K., Jury, W.A., Fluhler, H. and Attinger W., Transport of Chloride Through an Unsaturated Field Soil. Water Resour. Res. 7, Shalhevet, J., 199. Using water of marginal quality for production: major issues. Agric. Water Mgmt., Vol. 5, Topp, G.C., Davis, J.L. and Annan A.P., 19. Electromagnetic Determination of Soil Water Content: Measurements in Coaxial Transmission lines. Water Resour. Res. 1, Ward, A.L., Kachanoski R.G. and Elrick D.E., 199. Laboratory Measurements of Solute Transport Using Time Domain Reflectometry. Soil Sci. Soc. Am. J. 5, Younes, H.A., Gad, A., and Abdel Rahman, M., Utilization of different remote sensing techniques for the assessment of soil salinity and water table levels in the Serry Command area, Egypt. Egypt, J. Soil Sci. 33, No.,