physical properties of soils under sub-surface

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PHYSICAL PROPERTIES OF SOILS UNDER SUB-SURFACE DRAINAGE SYSTEM HAMID GUL, R.A KHATTAK, DOST MUHAMMAD and ZAHIR SHAH Department of Soil & Environmental Sciences, Khyber Pakhtunkhwa Agricultural University, Peshawar – Pakistan.

ABSTRACT The suitability of soil for crop production may be determined by its physical properties. These properties, for example, affect crop production through nutrients supply, water infiltration, and water holding capacity. In addition, they play an important role in influencing the behavior of plant growth. Keeping in view the significance of soil physical environment in relation to plant growth, this study was designed to determine and evaluate the physical properties of soils at various depths located in the Mardan SCARP area of Khyber Pakhtunkhwa Province (Pakistan) during 2003-04. The analysis of variance indicated non-significant changes in sand, silt and clay fractions with cropping sequence, but showed significant changes in sand and clay with soil depth. Sand particles decreased while clay increased with increasing soil depth. Soil permeability, leaching fraction and hydraulic conductivity, on the other hand, showed significant changes with cropping sequence and depth. Soil permeability and leaching fraction, for example, were greatest after maize than after or before wheat and both fractions increased with increasing depth. These results suggested that soil physical properties changed with increasing depth. Although cropping did not significantly influence the particle size distribution, it exerted significant influence on soil permeability, leaching fraction and hydraulic conductivity. It is important to note that this study will be useful to devise soil management practices for the Mardan SCARP area. Key Words: Soil permeability, leaching fraction, hydraulic conductivity, sand, clay, silt Citation: Gul, H., R.A. Khattak, D. Muhammad and Z. Shah. 2011. Physical properties of soils under sub surface drainage system. Sarhad J. Agric. 27(2): 225-232 INTRODUCTION The physical properties of soils play an important role in influencing the behavior of plant growth. Soil texture, for example, determines not only the nutrient supplying ability of soil solids but also the supply of water and air to plant life. On the other hand, leaching of solutes from agricultural soils is a serious environmental problem. The drainage characteristics have direct correlation with soil properties such as soil texture, structure, hydraulic conductivity and soil permeability. The root-zone salt balance can be controlled through management, and the irrigators can control the amount of salt applied, by adjusting the irrigation rate and salinity of irrigation water. The amount of salt leaching from the root-zone impacts the salt balance. The leaching fraction contributes to leaching salts from the root-zone and by changing the fraction can control the amount of salts leached and consequently the resulting soil salinity in the root-zone. The leaching fraction attainable under field conditions is affected by soil type. Hydraulic conductivity is an important soil property and depends upon soil particle size, the pore spaces in the soil and the difference in hydraulic head. Unlike the earlier Salinity Control and Reclamation Projects (SCARP) in Pakistan, the problems of water logging in Mardan were tackled by installation of tile drains. This was because of low hydraulic conductivities in the area that made it unlikely that the normal approach using deep tube wells for drainage would be successful. Low hydraulic conductivities restrict flow of water through natural drains and therefore, there are problems of persistent standing water on fields following periods of heavy rain falls. Hirekhan et al. (2007) reported that the sand content in the upper 1.8 m soil varied from 70 to 75% and the hydraulic conductivity of this layer was 1.0 m d-1. In the layer below 1.8 m soil texture varied from sand to loamy sand and the hydraulic conductivity of this layer was 7.5 m d -1. The average hydraulic conductivity of the profile was in the range of 2.0-2.5 m d -1. Ayers and Wescot (1989) reported that leaching fraction was affected by soil type, climate, irrigation management practices and irrigation water salinity. They also noted that in some instances, the leaching fraction could be much lower than leaching requirement, resulting in soil salinization and loss of crop productivity. Oosterbaan and Nijland (1994) reported that the hydraulic conductivity of the surface clay ranged from 0.005 to 0.01 m d -1 when measured with inverse auger hole method. They also observed that the hydraulic conductivity of weathered calcareous parent material ranged from 0.05 to 0.1 m d -1 when measured with normal auger hole method. Khattak and Perveen (1987) after analyzing soil samples collected from Peshawar and Charsadda reported that the texture of the soil samples of Mardan district ranged from sandy loam to clay and that of Peshawar and Charsadda ranged from sandy loam to silty clay loam. Bhatti (1997) reported that soils of Khyber Pakhtunkhwa Province (Pakistan) contained an average of 21 % sand. In the area under study (Mardan SCARP), the Canadian Drainage Team (1984) reported

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soil permeability of 0.15 to 2.13 m d-1 with an average of 1.01 m y-1 before the installation of the project. Sposito (1989) reported that the increase in Ca and K losses with increasing N rates could be associated with the formation of soluble complexes which promoted their mobility. Naeem (1998) observed that sand content decreased and clay content increased with increasing soil depth. This paper reports changes in physical properties of soil including particle size distribution, permeability, leaching fraction and hydraulic conductivity with cropping sequence and soil depth in Mardan SCRAP area. MATERIALS AND METHODS The following scientific approach was adopted to evaluate the physical characteristics from the selected sites in Mardan SCARP area during cropping seasons covering the period from 2003 to 2004. Soil Samples Collection To assess the soil’s physical characteristics as influenced by location, depth and timing of sampling, ten fields in each of the two sites were selected randomly. Wheat was grown in these fields in Rabi season (November to May) and maize in Kharif season (July to October) during 2003-2004. After dividing the area into 10 different sampling units, 3 pits with 1 x 2 m2 up to a depth of 270 cm were dug in each sampling unit for composite sampling at 0-45, 45-90, 90-135, 135-180, 180225 and 225-270 cm depths. Sixty samples from 10 locations with 6 depths in each site were collected during a given sampling time. The composit surface soil samples from the same sampling units at both sites were collected three times i.e. before wheat sowing (October 2003), after wheat harvest (May, 2004) and after maize harvest (October 2004). The samples were collected in properly labeled plastic bags and were transferred to Soil and Environmental Sciences Laboratory, Agriculture University, Peshawar for further processing. These soil samples were analyzed for soil texture, permeability, leaching fraction and hydraulic conductivity using standard analytical procedures.

Soil texture Soil texture was determined by the bouyoucos hydrometer method using USDA textural triangle (Gee and Bauder, 1986). Leaching Fraction Leaching fraction (LF) was determined from the amount of irrigation and drainage waters using the formula: Waterleach ed below root zone LF  Depth of water applied Hydraulic Conductivity Soil hydraulic conductivity was determined in undisturbed soils by the method described by Ritzema (1994). Hydraulic conductivity was calculated with the following formula:

Where

K=C

Ho - Ht t

K = Hydraulic conductivity (m d-1) C = a geometric factor of the soil t = time elapsed since the 1st readings of the level of the rising water in the hole (sec) Ho = Ht when t is equal to zero Ht = depth of water level in the hole below the reference level as time t (cm) Soil Permeability The soil permeability was determined in disturbed soil (< 2 mm particle size) packed in a special apparatus as described by Richard (1954). Statistical Analyses All the data were subjected to the analysis of variance (ANOVA) technique using simple factorial Randomized Complete Block design based on the number of variables in the particular study. The statistical analyses were performed by using MSTATC, SAS and Statistix computer programs. The Least Significant Difference (LSD) test was used to differentiate the effects of various factors (Steel and Torrie, 1980).

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RESULTS AND DISCUSSION Soil Particles Size Distribution Across sampling time, the average sand fraction ranged from 9.72 to 20 g 100-g-1 at site 1 and 2.00 to 22g 100-g-1 at site-2 (Table I). Sampling time did not significantly affect the sand fraction of the soil. However, the effect of depth was significant. The sand fraction progressively and significantly decreased with increasing soil depth (Fig. 1). Given the standard deviations for the mean of fields, depth and location, the observed variations may not seem large. However, a difference of few percent in sand, silt and clay can affect permeability and leaching of nutrients. Textural class of a given soil normally does not change with time but spatial variability within field and with depth in a given profile is well recognized and is not uncommon. The results are supported by the finding of Naeem (1998). Table-I

Changes in soil sand fraction (%) with sampling time and soil depths at two sites during 2003-04 under sub-surface tile drainage system ( n = 10) Time of sampling Grand Sampling depth Mean Before wheat After wheat After maize ----------------------------------------------------------Site-1, Fazliabad ----------------------------------------------------------------Depth (cm) Min Max Mean S.D. Min Max Mean S.D. Min Max Mean S.D. 0-45 12.00 15.00 14.20 0.88 13.00 17.00 14.28 1.06 13.95 15.30 14.49 0.47 14.32 45-90 12.00 16.00 13.96 1.11 12.00 14.00 13.43 0.66 13.50 14.50 14.01 0.31 13.80 90-135 11.90 17.00 13.56 1.56 11.00 15.20 13.00 1.13 12.30 15.00 13.26 0.84 13.27 135-180 11.00 18.00 13.09 2.02 10.00 15.00 12.66 1.30 11.00 14.37 12.43 1.06 12.73 180-225 11.28 20.00 12.94 2.64 9.72 17.00 12.22 1.88 10.78 13.00 11.67 0.72 12.28 225-270 10.00 19.00 11.92 1.30 10.00 16.40 11.62 1.86 10.00 11.22 10.63 0.50 11.39 Mean 11.36 17.50 13.28 1.59 10.95 15.77 12.87 1.32 11.92 13.90 12.75 0.65 12.97 Site-2, Manga Dargai 0-45 18.00 21.40 20.37 1.02 17.00 22.00 19.69 1.86 19.00 21.40 20.41 0.80 20.16 45-90 2.00 21.00 17.88 5.66 16.40 21.40 19.54 1.65 19.00 20.00 19.52 0.44 18.98 90-135 16.00 21.00 19.34 1.32 18.00 20.75 19.18 0.99 18.23 20.26 19.12 0.61 19.21 135-180 16.00 20.00 18.64 1.11 16.00 21.00 18.62 1.65 16.00 19.42 18.26 0.98 18.50 180-225 15.00 19.12 17.71 1.33 15.60 20.00 17.92 1.40 15.64 18.70 17.14 1.02 17.59 225-270 15.00 18.64 16.66 1.30 14.00 19.33 16.45 1.69 15.00 18.00 16.27 0.83 16.46 Mean 13.67 20.19 18.43 1.96 16.17 20.75 18.57 1.54 17.15 19.63 18.45 0.78 18.48 Averaged across depths and locations (RxDxL, n = 120) Before wheat 2.00 21.40 15.85 a 3.52 After wheat 9.72 22.00 15.72 a 3.34 After maize 10.00 21.40 15.60 a 3.26 LSD (p< .05) 0.55 Average across sampling times and locations (RxTxL, n = 60) 0-45 12.00 22 17.24 a 3.13 45-90 2.00 21.4 16.39 b 3.12 90-135 11.00 21 16.24 b 3.19 135-180 10.00 21 15.62 c 3.31 180-225 9.72 20 14.94 d 3.27 225-270 10.00 19.33 13.92 e 3.33 LSD (p< .05) 0.53 * Values with same letter(s) do not differ significantly at p < 0.05

Fig. 1.

Decrease in % sand with increase in soil depth (values are averages across location and sampling times)

The soils were predominantly silty. The mean silt values as determined in the three sampling periods were 70.07±2.69, 71.89±3.21 and 68.50±1.08 g 100-g-1 soil at site 1 and 67.08±1.5, 67.09±1.92, 68.51±1.10 g 100-g-1 at site 2 (Table II). Site-2 contained relatively (2 to 3 %) less silt as compared to site-1. The silt fraction, however, was not significantly affected by the sampling time or soil depth. Small changes in silt over a given field with time could be associated with uneven distribution of silt particles added through canal irrigation which contained appreciable amount of silt or silt might have been added through seasonal runoff in monsoon.

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Table-II

Changes in soil silt fraction (%) with sampling time and soil depths at two sites during 2003-04 under sub-surface tile drainage system ( n = 10) Sampling Time of sampling Grand depth Mean Before wheat After wheat After maize Site-1, Fazliabad Depth (cm) Min Max Mean S.D. Min Max Mean S.D. Min Max Mean S.D. 0-45 67.44 72.00 70.08 1.27 67.00 78.00 72.10 3.34 66.59 70.05 68.78 1.08 70.32 45-90 67.56 72.00 70.52 1.38 69.00 78.00 72.71 2.87 66.88 70.40 68.52 1.06 70.58 90-135 66.66 71.10 69.92 1.32 69.00 78.00 72.63 3.48 66.70 70.00 68.29 1.06 70.28 135-180 67.89 72.00 69.90 1.25 68.00 78.00 71.88 3.17 65.86 70.20 68.15 1.34 69.98 180-225 65.00 96.70 71.19 9.08 68.00 77.00 71.10 3.45 67.00 70.22 68.39 1.02 70.23 225-270 64.00 71.35 68.80 1.87 68.00 76.00 70.90 2.94 67.58 70.00 68.86 0.94 69.52 Mean 66.43 75.86 70.07 2.69 68.17 77.50 71.89 3.21 66.77 70.15 68.50 1.08 70.15 Site-2, Manga Dargai 0-45 64.67 70.00 67.69 1.65 65.00 71.00 67.50 1.72 65.90 70.00 68.36 1.21 67.85 45-90 66.00 69.00 67.35 1.20 65.00 68.00 66.88 1.08 67.02 70.03 68.47 0.99 67.57 90-135 65.94 68.14 67.28 0.68 64.00 70.00 67.50 1.84 67.20 69.17 68.23 0.67 67.67 135-180 64.00 69.00 67.33 1.57 61.00 70.00 66.83 2.62 67.00 71.02 68.13 1.22 67.43 180-225 62.00 68.76 66.52 2.06 59.00 68.00 66.34 2.65 67.00 70.96 68.81 1.38 67.22 225-270 63.00 68.00 66.32 1.87 64.00 70.00 67.47 1.64 67.90 71.00 69.09 1.11 67.62 Mean 64.27 68.82 67.08 1.50 63.00 69.50 67.09 1.92 67.00 70.36 68.51 1.10 67.56 Averaged across depths and locations (RxDxL, n = 120) Before wheat 62.00 96.70 68.57 b 3.29 After wheat 59.00 78.00 69.49 a 3.56 After maize 65.86 71.02 68.51 b 1.09 LSD (p< .05) 0.55 Average across sampling times and locations (RxTxL, n = 60) 0-45 64.67 78 69.09 a 2.40 45-90 65.00 78 69.08 a 2.47 90-135 64.00 78 68.97 a 2.59 135-180 61.00 78 68.70 a 2.69 180-225 59.00 96.7 68.73 a 2.83 225-270 63.00 76 68.57 a 2.99 LSD (p< .05) 0.79 * Values with same letter(s) do not differ significantly at p < 0.05

Fig. 2. Increase in % clay with increase in soil depth (values are averages across location and sampling times)

The data for the given location and mean values for field and depth of samples indicated that site-1 had higher amount of clay particles as compared to site-2 (Table III). . The clay fraction was not significantly influenced by the sampling time. However, it was progressively and significantly influenced with increasing soil depth. As pointed out earlier, small changes with time could be associated with impact of irrigation waters containing more silt size particles which induced changes in the clay distribution in a given field. Increases in the clay content with depth (Fig. 2) suggested downward movement of clay particles with drainage waters in the high coefficient tile drainage system exerting internal downward pressure.

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Table-III

Changes in soil clay fraction (%) with sampling time and soil depths at two sites during 2003-04 under sub-surface tile drainage system ( n = 10) Sampling Time of sampling Grand depth Mean Before wheat After wheat After maize Site-1, Fazliabad Depth (cm) Min Max Mean S.D. Min Max Mean S.D. Min Max Mean S.D. 0-45 14.00 18.00 15.73 1.07 9.00 16.00 13.62 2.86 15.81 18.11 16.73 0.71 15.36 45-90 13.00 18.44 15.52 1.67 10.00 17.00 13.86 2.77 16.00 18.72 17.47 0.85 15.62 90-135 14.00 19.00 16.52 1.47 9.00 18.00 14.37 3.31 17.30 19.13 18.46 0.63 16.45 135-180 13.00 19.00 17.02 1.94 10.40 20.00 15.46 2.89 18.80 20.20 19.39 0.48 17.29 180-225 15.00 20.00 18.54 1.73 11.00 21.00 16.68 3.52 18.87 20.98 19.83 0.66 18.35 225-270 16.00 22.00 19.28 1.46 12.24 21.00 17.43 3.22 20.00 21.52 20.71 0.56 19.14 Mean 14.17 19.41 17.10 1.56 10.27 18.83 15.24 3.10 17.80 19.78 18.76 0.65 17.03 Site-2, Manga Dargai 0-45 10.00 14.00 11.94 1.17 10.00 15.00 12.81 1.34 10.00 13.00 11.43 0.95 12.06 45-90 10.00 14.00 12.97 1.42 10.60 15.60 13.58 1.46 10.00 13.30 12.11 1.09 12.89 90-135 12.00 16.00 13.38 1.32 10.00 16.00 13.33 1.70 11.83 14.00 12.65 0.71 13.12 135-180 11.40 16.00 14.03 1.47 11.00 19.00 14.55 2.01 12.80 14.70 13.61 0.68 14.06 180-225 13.06 20.00 16.17 2.34 13.00 22.00 15.94 2.55 12.70 15.00 14.05 0.93 15.39 225-270 15.22 20.00 17.02 1.46 13.00 20.00 16.08 1.75 13.00 16.00 14.64 0.99 15.92 Mean 11.95 16.67 14.25 1.53 11.27 17.93 14.38 1.80 11.72 14.33 13.08 0.89 13.91 Averaged across depths and locations (RxDxL, n = 120) Before wheat 10.00 22.00 15.68 a 2.64 After wheat 9.00 22.00 14.81b 2.82 After maize 10.00 21.52 15.92 a 3.21 LSD (p< .05) 0.38 Average across sampling times and locations (RxTxL, n = 60) 0-45 9.00 18.11 13.71 e 2.43 45-90 10.00 18.72 14.25 ed 2.50 90-135 9.00 19.13 14.78 d 2.56 135-180 10.40 20.2 15.68 c 2.51 180-225 11.00 22 16.87 b 2.51 225-270 12.24 22 17.53 a 2.53 LSD (p< .05) 0.55 * Values with same letter(s) do not differ significantly at p < 0.05

Fig. 3. Increase in soil permeability with increase in soil depth (values are averages across location and sampling times)

Soil Permeability Soil permeability data revealed relatively higher values for site-2 as compared to site-1; (Table-IV). This observation negatively correlated to the clay content, which was higher in site-1 and lower in site-2. The permeability of these soils could be considered as low to medium, with values mostly ranging from 0.42 to 0.67 mm d-1 in site-1 and from 0.46 to 0.67 mm d-1 in site-2 with grand mean of 0.55 and 0.57 mm d-1, respectively. It is important to note that the soil permeability tended to progressively increase with increasing soil depths (Fig. 3), and when averaged across replications x depth x location, it increased with depth with 0.01 mm d-1 increments (Table-V) Through the increase in clay content with depth should have minimize the soil permeability with depth but since the the increase in clay content was too low (fraction of percent) to affect it at large. The soil permeability was also influenced significantly by the sampling period. It appeared that soil permeability increased gradually and significantly with cropping.

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Changes in soil permeability (mm d-1) with sampling time and soil depths at two sites during 2003-04 under subsurface tile drainage system ( n = 10) Time of sampling Sampling depth Grand Mean Before wheat After wheat After maize Site-1, Fazliabad Depth (cm) Min Max Mean S.D. Min Max Mean S.D. Min Max Mean S.D. 0-45 0.42 0.63 0.52 0.06 0.43 0.50 0.47 0.02 0.42 0.52 0.47 0.04 0.49 45-90 0.46 0.58 0.54 0.05 0.46 0.60 0.51 0.04 0.47 0.54 0.51 0.02 0.52 90-135 0.45 0.67 0.55 0.07 0.46 0.60 0.54 0.04 0.50 0.60 0.56 0.04 0.55 135-180 0.43 0.63 0.54 0.06 0.48 0.62 0.58 0.04 0.57 0.64 0.60 0.03 0.57 180-225 0.47 0.67 0.55 0.07 0.43 0.66 0.60 0.07 0.62 0.64 0.63 0.01 0.59 225-270 0.48 0.60 0.52 0.04 0.49 0.65 0.61 0.05 0.54 0.67 0.63 0.04 0.59 Mean 0.45 0.63 0.54 0.06 0.46 0.61 0.55 0.04 0.52 0.60 0.57 0.03 0.55 Site-2, Manga Dargai 0-45 0.48 0.61 0.55 0.05 0.48 0.56 0.52 0.03 0.48 0.55 0.52 0.02 0.53 45-90 0.47 0.62 0.53 0.05 0.52 0.60 0.56 0.03 0.52 0.61 0.57 0.03 0.55 90-135 0.46 0.64 0.55 0.06 0.50 0.60 0.56 0.03 0.50 0.60 0.56 0.03 0.56 135-180 0.48 0.63 0.57 0.04 0.54 0.61 0.58 0.03 0.56 0.63 0.59 0.03 0.58 180-225 0.48 0.60 0.54 0.04 0.55 0.67 0.63 0.04 0.57 0.67 0.62 0.03 0.60 225-270 0.50 0.60 0.56 0.04 0.58 0.66 0.63 0.03 0.60 0.66 0.64 0.02 0.61 Mean 0.48 0.62 0.55 0.05 0.53 0.62 0.58 0.03 0.54 0.62 0.58 0.03 0.57 Averaged across depths and locations (RxDxL, n = 120) Before wheat 0.42 0.67 0.54 c 0.05 After wheat 0.43 0.67 0.56 b 0.06 After maize 0.42 0.67 0.58 a 0.06 LSD (p< .05) 0.01 Average across sampling times and locations (RxTxL, n = 60) 0-45 0.42 0.63 0.51 e 0.05 45-90 0.46 0.62 0.54 d 0.05 90-135 0.45 0.67 0.55 c 0.05 135-180 0.43 0.64 0.58 b 0.04 180-225 0.43 0.67 0.59 a 0.05 225-270 0.48 0.67 0.60 a 0.04 LSD (p< .05) 0.01 * Values with same letter(s) do not differ significantly at p < 0.05 Table-IV

Fig. 4.

Increase in leaching fraction with increase in soil depth (values are averages across location and sampling times)

Leaching Fraction (LF) The mean values of LF for the 3 sampling periods was 0.23±0.04, 0.25±0.04 and 0.24±0.04, for site 1 and 0.22±0.04, 0.23±0.03 and 0.24±0.04 for site 2 (Table V). There was an increase in LF with cropping. The observed values of LF are considered ideal for avoiding salt build up in soil (Sposito, 1989). The LF increased somehow with increasing depth up to 135 cm but declined with further increase in depth (Fig. 4). Hydraulic Conductivity (HC) The mean hydraulic conductivity determined in the surface soils (0 – 45cm) was 1.18±0.13, 1.07±0.13 and 1.22±0.12 mm d-1 in site 1 and 1.35±0.09, 1.20±0.05 and 1.26±0.10 mm d-1 in site 2 for the three consecutive soil sampling (Table VI). The mean values for site-2 were larger than the mean values of site 1. for the corresponding periods. The higher HC values in site-2 might be due to lower clay content than in site-1 in the given surface soil. Hydraulic Conductivity decreased somehow with the cropping.

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Table-V Changes in soil leaching fraction (mm d-1) with sampling time and soil depths at two sites during 2003-04 under sub-surface tile drainage system ( n = 10) Sampling Time of sampling Grand depth Mean Before wheat After wheat After maize Site-1, Fazliabad Depth (cm) Min Max Mean S.D. Min Max Mean S.D. Min Max Mean S.D. 0-45 0.16 0.28 0.22 0.03 0.18 0.32 0.22 0.05 0.18 0.22 0.20 0.01 0.21 45-90 0.17 0.30 0.23 0.04 0.19 0.31 0.27 0.05 0.20 0.29 0.26 0.03 0.25 90-135 0.20 0.32 0.28 0.03 0.17 0.32 0.23 0.04 0.19 0.37 0.25 0.06 0.25 135-180 0.16 0.30 0.21 0.05 0.17 0.29 0.23 0.04 0.18 0.33 0.25 0.05 0.23 180-225 0.15 0.28 0.23 0.04 0.21 0.30 0.25 0.03 0.19 0.30 0.22 0.04 0.23 225-270 0.16 0.25 0.20 0.03 0.22 0.32 0.28 0.04 0.18 0.31 0.25 0.05 0.24 Mean 0.17 0.29 0.23 0.04 0.19 0.31 0.25 0.04 0.19 0.30 0.24 0.04 0.24 Site-2, Manga Dargai 0-45 0.16` 0.24 0.19 0.02 0.15 0.22 0.20 0.02 0.18 0.28 0.21 0.03 0.20 45-90 0.18 0.32 0.27 0.04 0.23 0.31 0.27 0.03 0.19 0.32 0.25 0.04 0.26 90-135 0.13 0.30 0.23 0.05 0.21 0.30 0.25 0.03 0.18 0.30 0.25 0.04 0.24 135-180 0.18 0.29 0.21 0.04 0.18 0.30 0.24 0.04 0.18 0.30 0.25 0.04 0.23 180-225 0.16 0.30 0.21 0.04 0.19 0.27 0.22 0.03 0.19 0.30 0.26 0.04 0.23 225-270 0.16 0.27 0.22 0.03 0.19 0.30 0.22 0.03 0.18 0.32 0.23 0.06 0.22 Mean 0.16 0.29 0.22 0.04 0.19 0.28 0.23 0.03 0.18 0.30 0.24 0.04 0.23 Averaged across depths and locations (RxDxL, n = 120) Before wheat 0.13 0.32 0.22 b 0.04 After wheat 0.15 0.32 0.24 a 0.04 After maize 0.18 0.37 0.24 a 0.05 LSD (p< .05) 0.01 Average across sampling times and locations (RxTxL, n = 60) 0-45 0.15 0.32 0.21 c 0.03 45-90 0.17 0.32 0.26 a 0.03 90-135 0.13 0.37 0.25 a 0.03 135-180 0.16 0.33 0.23 b 0.04 180-225 0.15 0.3 0.23 b 0.04 225-270 0.16 0.32 0.23 b 0.03 LSD (p< .05) 0.01 * Values with same letter(s) do not differ significantly at p < 0.05 Table-VI Changes in soil hydraulic conductivity (mm d-1) with sampling time and soil depths at two sites during 2003-04 under subsurface tile drainage system ( n = 10) Sampling Time of sampling Grand depth Mean Before wheat After wheat After maize Site-1, Fazliabad Depth (cm) Min Max Mean S.D. Min Max Mean S.D. Min Max Mean S.D. 0-45 0.96 1.30 1.18 0.13 0.91 1.28 1.07 0.13 0.93 1.34 1.22 0.12 1.16 Site-2, Manga Dargai 0-45 1.16 1.46 1.35 0.09 1.13 1.27 1.20 0.05 1.11 1.40 1.26 0.10 1.27 Averaged across locations (RxL) Before wheat 0.96 1.46 1.26 a 0.14 After wheat 0.91 1.28 1.13 b 0.11 After maize 0.93 1.40 1.23 a 0.12 LSD (p < .05) 0.06 Average across sampling times and locations (RxTxL, ) 0-45 0.91 1.46 1.21 0.13 * Values with same letter(s) do not differ significantly at p < 0.05

CONCLUSION It can be concluded that there were considerable variations in the physical properties of soil at both sites which were subjected to heavy sub surface drainage system. Although cropping did not significantly influence the particle size distribution, it significantly influenced the soil permeability, LF and HC. The physical properties of soil changed significantly with increasing depth. It is therefore recommended that scientific soil management with advanced technologies be adopted. REFERENCES Ayers, R.S. and D.W. Weskot. 1989.Water Quality for Agriculture. FAO report of the United Nations. FAO, Rome. Bhatti, A.U. 1997. Irrigated soils of Khyber Pakhtunkhwa: Water Management in Khyber Pakhtunkhwa. pp 96-111. In D. Hamm, M. Rust, J. Edward, V. Vander and H. Rehman (Eds). Agric. Univ. Peshawar and Deptt.. of Irrig. & Soil & Water Conservation, Wageningen Agric. Univ., The Netherland. Canadian Drainage Team. 1984. Mardan SCARP Sub-surface drainage design analysis. Report prepared by Canadian drainage team in consultation with HAZRA/NESPAK consultants for Mardan SCARP and submitted to WAPDA Pakistan. 224 pages.

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