Sarhad J. Agric. Vol. 23, No. 2, 27 IMPACT OF WATER TABLE DEPTHS ON THE PHYSICAL PROPERTIES OF SALT AFFECTED SOIL AND YIELD OF SUGARCANE IN MARDAN SCARP AREA Gul Daraz Khan*, Moin Shah*, M. Tariq**, Muhammad Zubair khan* and Naveedullah* ABSTRACT A field study was conducted to study the impact of different Water Table Depths (WTD) on selected soil physical properties of salt affected soil and yield of sugarcane in Mardan SCARP area from September 2 to May 21. Five drainage units (16, 17, 18, 122 and 129) were selected in which observation wells were installed to monitor the water table depths. Field tests were conducted to determine steady state infiltration rate and the hydraulic conductivity at the selected plans. Sugarcane yield data were collected through sampling in the drainage units having different characteristics. All the required data were collected at the head (H), middle (M) and tail (T) of the selected collectors in each drainage unit. The average WTD of plans 16, 18 (farmers controlled collectors), 122 (badly managed blocked collector), 17, and 129 (well-managed free flowing collectors) were 1.67, 1.53, 1.16, 2.17 and 1.9 m, respectively from the ground surface. There was a rising trend in WTD at the tail of the controlled collectors. The average WTD of free flowing drainage units were relatively deeper than controlled ones. On the other hand steady state infiltration rate and average hydraulic conductivity were in the range of 9.36 14.8 mm h -1 and.31 1.98 m day -1, respectively and were highest for well managed free flowing plans, and lowest for badly managed blocked plan. Average yield of sugarcane in all the above mentioned drainage units were in the range of 36.99 52. t ha -1 and was highest in one of the farmers blocked drainage unit and lowest in badly managed blocked drainage unit. The yield of sugarcane was optimum at a WTD of 1.2-1.9 m and lowest at <1 m or >2 m from the ground surface. The overall results indicated that an optimum sugarcane yield can be obtained in Mardan SCARP area by maintaining water table from ground surface in the range of 1.2 1.9 m. INTRODUCTION Salinity control and reclamation projects (SCARP) in different parts of the country was started to lower the water table and to reclaim the irrigated saline waste area into productive ones. In the beginning vertical drainage system was introduced in the highly permeable aquifer of Punjab by boring 13, deep tube wells. But in low permeable aquifer of the country like Mardan irrigated areas, horizontal subsurface tile drainage system was preferred to be installed over vertical drainage system. This area encompasses 5, hectares of 54,5 total cultivable command area of the lower swat irrigation canal. After implementation of this type of subsurface drainage system, water table got much lower than the design one (1.1 m) in some areas, which created two main problems i.e. high water demand and attack of termites on crops. To overcome these problems some farmers tried to control the main collectors in a struggle to restore the water table for maximum ground water contribution to the crop water requirements. Thus they intervened in the already implemented system of SCARP. Indigenous work indicated that the yield in the non-waterlogged area was double as compared to the waterlogged conditions (Kakar, 2). Similarly, Khan et al. (1997) also compared the yield of sugarcane before and after the Mardan SCARP implementation, which was 33.96 and 58.26 t ha -1, respectively. Gupta and Yadav (1995) also reported that sugarcane yield was significantly decreased at a depth of 2 cm below the surface. Therefore, the present study was designed to assess the impact of different water table depths as influenced by the farmers intervention and maintenance status of the selected plans, in relation to some physical properties of soil such as infiltration rate, hydraulic conductivity and movement of water into and through the soil profile and yield of sugarcane. As Kahlown and Iqbal (1999) reported that a water table depth of greater than 2 m was found more favorable for cotton, 1 to 2 m for wheat and sugarcane, and less than 1 m for rice. Moreover, Shermohammadi and Skaggs (1984) determined the effect of surface condition, initial water content and shallow water table on infiltration rate. They observed that infiltration rate was higher in deep water table than in shallow water table. However, in the present project impact of water table depth in different types of managed subsurface system has been studied. The first subsurface drainage system has been controlled with a technique to raise its water level. In second one the open drain of the collective system was blocked due to deposition of silt, which clogged the relative upstream adjoining closed system, known as badly managed due to improper operational strategies of the system. The third type drainage system is operating according to basic design of the system. However, these three types subsurface drainage systems have been assessed with respect to physical properties such as infiltration rate and hydraulic conductivity in relation to sugarcane yield with the main objective, to study the impact of different water table depths on the selected physical * Department of Water Resources Management, NWFP Agricultural University Peshawar Pakistan. ** Department of Soil and Environmental Sciences, NWFP Agricultural University Peshawar Pakistan.
Gul Daraz Khan, et al. Impact of water table depths on the physical properties 352 properties of soil and yield of sugarcane in Mardan SCARP area. MATERIALS AND METHODS Site Selection Sub-surface tile drainage system at Mardan SCARP was installed from 1982-1987 in contract 1 area and from 1987 1992, in contract II area of Mardan. Contract I area consists of 36 drainage plans (11-136), where as contract II area consists of 88 drainage plans (2-25 and 3-338). The contract I area had shallow water table depth (-1.22 m) before implementation of the sub-surface drainage system as compared to contract II area having deeper water table depth (1.22 2.13 m). The contract I was further divided into two sub-groups of water table. The first part was mostly abandoned while the second one was still on optimum in terms of multi cropped growth and yield. In order to analyze the physical properties along with yield of sugarcane at different water table depths in plans 16, 17, 18, 122 and 129. Plans 16 and 18 have been selected from the area controlled by the farmers with a view to raise the water table in their fields for maximum ground water contribution. Plans 17 and 129 had well managed open collectors, while the collector of plan 122 was partially closed due to badly managed poor conditions of the open drain. In the plans 16 and 18 collectors were controlled by the farmers with a view to raise water level in their fields for maximum ground water contribution to the crop water requirements. Determination of Infiltration Rate Infiltration rate was measured with the help of double ring infiltrometer in the field. Double ring infiltrometer consists of two concentric rings. It was placed at the ground surface and a metal lid was placed on the top of the rings, the lid was then hammered to press the rings few centimeters into the ground. A float containing the scale was fixed on the top of the inner ring, which indicates the water infiltrated into the soil. The inner ring was covered with the plastic sheet to prevent any infiltration while pouring the water into the ring. The outer ring was filled with water first and then the inner one. The plastic was then removed and initial reading was taken. The second and third readings were taken with 3 seconds intervals. The fourth reading was taken after 1 minute. The fifth, sixth, seventh and eighth reading were taken at two minutes interval each. The other four reading were taken at five minutes intervals. The next four readings were taken for 1 minutes interval. After that 2 and 3 minutes readings were taken three times each. The last reading was taken after 1 hour. In this way at least five hours were spent on single test only. Computation of Cumulative Infiltration Cumulative infiltration and infiltration rate were computed by adding the difference in infiltration depth and by dividing the depth of water infiltrated into the soil with the time. Equations were developed to relate infiltration with time with the help of Kostiakov s equation, which is: Where F = a T b F = Cumulative infiltration (mm) a and b = constant T = time (min) Determination of Hydraulic Conductivity Auger hole method was used to determine hydraulic conductivities. It can be used to measure the hydraulic conductivity in situ below a water table. Fifteen hydraulic conductivity tests were carried out three each at head middle and tail of the selected collector in each plan number. A hole was bored into the soil with an auger to a certain depth below the water table. A float was attached to a lightweight steel tape and steel tape was then fixed to a standard rod. Standard rod was pressed into the soil near the hole up to a certain mark so that the level readings could be taken at fixed height above the ground surface. When the water in the hole reached equilibrium with ground water, its depth from the reference point above the ground surface was measured. A part of water was then removed with the help of bailer. The steel tape with float was then lowered into the hole as quickly as possible. The groundwater then began to seep into the hole and the rate at which it raised was measured. Measurements were continued until recovery of the water in the hole equaled to about 2% of the depth of water initially bailed out. The same procedure was repeated twice for a single bore hole. Calculation of hydraulic conductivity Data collected from auger hole field tests were transferred to the computation sheet. Depth of the static water table (E) from the ground surface was computed by subtracting the length of the standard rod from the total length of tape and rod between float bottom and zero mark. Depth of water from the static water table to the bottom of the hole (H) was calculated by subtracting the static water table depth (E) from the total depth of the hole (H+E). Then.8 Yo was determined by multiplying the first draw down depth by.8. all the draw down depths which were lower than.8 Yo were discarded. Y was
Sarhad J. Agric. Vol. 23, No. 2, 27 353 computed by taking average of the first and last selected draw down depths, whereas Y was determined by subtracting the last draw down depth from the first one. Similarly, t was determined by the difference of the last and first selected time intervals. The hydraulic conductivity was calculated in m/day by using the following formula. K = H ( r 4* r * Y Y + 2)(2 ). Y t H Where K = hydraulic conductivity (m day -1 ) r = radius of the bore hole (cm) Y = difference of first and last draw down depths (cm) Y = average of first and last draw down depths (cm) H = water table depth from the static water table to the bottom of the hole (cm) t = difference of last and first selected time interval (sec.) Sugarcane Yield The yield data for sugarcane crop was collected at the head, middle and tail of each area in the experimental site. The samples on one square meter from the truly represented locations were physically harvested after maturity of crops in each field. Analytical balance was used for measuring the practical weight of each sample. Statistical Analysis The entire data for each parameter was subjected to correlation and regression, using a computer program Microsoft Excel (Steel et al., 1997). The different parameters like water table depth, infiltration rate and hydraulic conductivities were directly used or generated from the baseline instrumental data. RESULTS AND DISCUSSION Effect of Farmers Intervention Status on WTD Observation wells were installed at the head, middle and tail of the selected collector in all five plans such as 16, 18, 17, 129 and 122. The trend in change of WTD at various selected locations in the plans is shown in Figure 1. 3 W T D ( H ) W T D ( M ) W T D ( T ) 2.5 2 1.5 1.5 1 2 2 1 6 1 8 1 2 9 1 7 P la n s Fig. 1 Water table depths in the selected plans Plans 16, 18 and 122 showed similar trend of change in WTD. However, here the WTD is lowest from the ground surface at the middle and highest at the tail of collector. The reason is that the collectors in these plans were blocked and were discharging no or very little amount of water to the open drain. Water drained from the middle and head cumulated at the tail portion of collector. This resulted in rise of water level at the tail. The water level at head was close to ground surface than at middle for the obvious reason of seepage from canals. The plans 17 and 129, well managed open collectors, showed similar trend in change of WTD at the head, middle and tail of collector. In theses plans water level is going on deeper and deeper along the collector from head towards the tail. Because, the water table is highest at the head of the collector due to seepage from the canal and lowest at the tail due to deep open drain.
Sarhad J. Agric. Vol. 23, No. 2, 27 354 Table I. Impact of different water table depths on the physical properties of soil and yield of sugarcane Plans WTD (m) Infiltration rate (mm h -1 ) Hydraulic conductivity (m day -1 ) Yield (t ha -1 ) 122-H 1.1 9.3.9 34.34 122-M 1.5 1.1.74 44.65 122-T.9 8.68.6 31.98 16-H 1.9 13..97 4.26 16-M 2.1 13.1 1.4 39. 16-T 1.2 12.4.79 41.45 18-H 1.6 13.5 1.5 53.23 18-M 1.8 14. 1.6 52.12 18-T 1.2 13.7 1.2 5.65 129-H 1.5 14. 1.67 53. 129-M 1.9 14.4.69 52.32 129-T 2.3 14.6 1.7 39.2 17-H 1.5 14.7 1.78 49.24 17-M 2.3 14.7 2. 43. 17-T 2.7 15. 2.16 41.54 Effect of Water Table Depth on Infiltration Rate Steady state infiltration rate and WTD at head, middle and tail of the selected collector for each plan is presented in Table I. Results showed that the value of steady state infiltration rate was lowest (average value of 9.36 mm h -1 ) in badly managed plan, and highest in well managed plans (average values of 14.8 and 14.2 mm h -1 ). The plans having controlled collector (16 and 18) had average infiltration values of 12.8 and 13.7 mm h -1. The infiltration rate was lowest in plan 122, because of its silty clay nature in the top layers. Moreover, low infiltration rate was due to deep WTD (Shermohammadi and Skaggs, 1984). Another cause may be the lack of proper drainage by the partially closed collector. Whereas the causes for highest infiltration rate in plan 17 may be the deep water table depth and presence of termites that improved structure by decomposing green manure and farm yard manure to organic matter to restore well maintained status of the plan. The overall relationship between steady state infiltration and depth to water table from ground surface is shown in Figure 2. Results shows that there was no significant correlation between WTD and steady state infiltration. However, the steady state infiltration rate increased with increase in water table depth from ground surface. This could be due to the improvement of structure by microorganisms and deep root establishment of the crop in a larger space provided by deeper water table depth. Infilteration rate (mm h-1) 18 16 14 12 1 8 6 4 2 y = 2.6576x + 8.5259 R 2 =.4626.5 1 1.5 2 2.5 3 Fig. 2 Relationship between infiltration rate and WTD in the selected plans
Sarhad J. Agric. Vol. 23, No. 2, 27 355 Effect of Water Table Depth on Hydraulic Conductivity Hydraulic conductivities at the head, middle and tail of the selected plans are given in Table I. Results showed that hydraulic conductivity is minimum (average value of.31 m day -1 ) for plan 122, and maximum (average value of 1.98 m day -1 ) for plan 17, where as the average hydraulic conductivity values for plans 129, 18 and 16 were 1.35, 1.43 and 1.4 m day -1 respectively. There are some valid reasons for the low, especially in plan 122 hydraulic conductivity. One of the reasons for low hydraulic conductivity values is soil texture (silty clay loam and silty loam) in the top 15 cm layer. However, soil texture is not the only reason for difference in hydraulic conductivity in the selected plans, especially that of 122 and 17, because almost all the selected plans have either silt loam, clay loam or loamy soil texture (Khan and Awan 1992). But, the more important reason for low hydraulic conductivity in plan 122 may be some chemicals properties causing clay dispersion and pores plugging. This was in agreement with the findings of Abu-Sharar (1985). On the other hand the hydraulic conductivity of plan number 17 was maximum because of deeper WTD. The deeper WTD provided more space for microorganisms and termite activities that decompose green manure and farmyard manure to organic matter, which in turn improves soil structure and hence hydraulic conductivity. Deep WTD also provides larger space for root establishment to a greater depth, improving the soil structure for with increased hydraulic conductivity. Thus it can be said that some specific reasons of higher hydraulic conductivity values of plan 17, 129 (free discharging collectors) were those of deep water table depth from the ground surface and lowest chemical cumulation due to dynamic hydraulic properties. Figure 3 demonstrates the overall status of hydraulic conductivity with WTD in the selected plans. The above relation shows a significant correlation between WTD and K values at 5 % level of significance. The value of K increases with increase in WTD from the ground surface. Similar results were reported by Khan and Awan (1992 ). K. Saturation (m day-1) 2.5 2 1.5 1.5 y =.8969x -.2898 R 2 =.5241.5 1 1.5 2 2.5 3 Fig. 3 Relationship between saturated hydraulic conductivities and water table depths in the selected plans Effect of Water Table Depth on the Yields of Sugarcane The impact of different WTD ranges on the yield of sugarcane has been studied in general and specifically for the selected plans (Table I). The drainage unit 122 (badly managed) has average sugarcane yield of 36.99 t ha -1, at an average WTD of 1.16 m. Here, the yield was lowest at tail (31.98 t ha - 1 ) of the collector due to the shallow WTD of.9 m, comparatively highest than all the plans. The yield was relatively higher having 44.65 t ha -1, though values are appreciably high, but still within the safe limit at middle of the plan 122. The cause of good yield at this location could be due to suitable WTD for the crop that result in high ground water contribution to crop water requirements. Plan 18 (controlled by the farmer) had remarkable yield of 52. t ha -1 at an average WTD of 1.53 m. In this plan the WTD was in the best suitable range at all locations and hence maximum ground water contribution to the crop water requirements was ultimately observed. Plan 16 has relatively higher values of yield at tail and middle than at head for more or less the same above-mentioned reasons. Plan 129 (well-managed open drainage unit) has its highest yield of 53. and 52.32 t ha -1 at head and middle portion, respectively. The reason was maximum ground water contribution for the crop water requirement from the suitable WTD level in the fields. In plan 17 (open collector) yield of sugarcane
Sarhad J. Agric. Vol. 23, No. 2, 27 356 was highest at head with an average value of 49.24 t ha -1 at a WTD of 1.5 m. The yield of the same plan decreased at the middle and tail portion due to lowering of WTD from the surface. Here, the average yield at middle and tail was 43. and 41.54 t ha -1 at 2.3 and 2.7 m WTD, respectively. The farmers at tail had a complaint of water shortage to their crop and termite in their fields (From a blocked Questionnaire Performa with farmers). Figure 4 depicts the overall relationship of sugarcane yield with WTD. Results showed that yield of sugarcane was the highest between the range of 1.2-1.9 m and the lowest at a WTD of less than 1 m. Similarly, there was a decreasing trend of crop yield when WTD increased beyond 2 m. These results are closed to the findings of Kahlown and Iqbal (1999). On the basis of above results it can be said that sugarcane crop need a suitable range of WTD, for high ground water contribution to the crop water requirements and yield. 6 5 y = -15.363x 2 + 54.73x -.2636 R 2 =.3863 Yield t ha-1 4 3 2 1.5 1 1.5 2 2.5 3 Fig. 4 Relationship between sugarcane yield and WTD (-3 cm) of soil in the selected plans CONCLUSION Hydraulic conductivity and infiltration rate of the soil increased with the lowering of WTD. The hydraulic conductivity and infiltration rate of physically managed free flowing drainage unit (12) was 85 and 37% less than that of the well managed free flowing drainage unit (17). Sugarcane yield were optimum at WTD of 1.2-1.9 m and lowest at WTD <1 m or > 2 m. REFERENCES Abu-Sharar, T.M. 1985. Stability of soil structure and reduction in hydraulic conductivity as affected by electrolyte concentration and composition. Ph.D. Thesis, Univ. of California, Riverside (Dissertation. Abst. DAO 57568). Gupta, R. and R.L. Yadav. 1995. Contribution of groundwater to evopotranspiration of sugarcane during summer. Indian Sugar. 4:12, 887-89. Kahlown, M.A. and M. Iqbal. 1999. Impact of water logging and salinity on crop yield. Pak. Water and Power Dev. Authority. Public. No. 217. pp. 98-19. Kakar, M.A. 2. Diagnostic study of water logging and salinity at Surizai Peshawar. M.Sc.(Hons). Thesis, submitted to NWFP Agric. Univ., Peshawar - Pakistan. Khan, J.M. and S. Awan. 1997. Development of drainage database for Mardan SCARP and brief analysis of the hydraulic conductivity data. In: Water management in NWFP. Ed. D. Hammond Murrey-Rust, Edwar J. Vander Veld and Habib-ur-Rehman. Deptt. of Water Mgt. NWFP Agric. Univ., Peshawar - Pakistan. Khan, M.J., D.H. Murray Rust and T. Sarwar. 1997. Agricultural impact assessment of SCARP, Mardan. Water management in NWFP. Deptt. of Water Mgt, NWFP Agric. Univ., Peshawar - Pakistan. pp. 144-157. Shermuhammadi, A. and R.W. Skaggs. 1984. Effect of soil surface conditions on infiltration for shallow water table soil. Transactions of the ASAE. 27(6). Steel, R.G.D., J.H. Torrie and D.A. Dickey. 1997. Principles and procedures of statistics. A biometrical approach. 3rd. ed. McGraw Hill Co., Inc. New York, USA.