IMPACT OF CONTROLLED AND FREE DRAINAGE ON SOIL SALINITY IN MARDAN SCARP, THROUGH LONG TERM SIMULATION OF SOLUTE TRANSPORT MODEL ( LEACHC)

Abstract

Field study was conducted to determine the impact of controlled and free drainage on soil salinity from September 2004 to September 2005 in drainage unit 106 for long term simulation of solute transport of Mardan Salinity Control and Reclamation Project (SCARP) NWFP Pakistan. Leaching Estimation and Chemistry (LEACHC) model was calibrated for 44 days. The model was simulated for one, two and five years respectively, under controlled and free drainage at one meter water table depth. Simulation indicated different patterns of salinity related to water table depths under each condition. In controlled condition, the salt trend to accumulate at the upper part of root zone mainly due to evaporation. While the salinity under free condition showed fluctuation according to the actual field condition. Result indicated that at controlled drainage of 1.0m watertable depth, soil electrical conductivity (EC) increased to 2.42 dS/ m, 3.97 dS/ m and 6.14 dS/ m after 1, 2 and 5 years of simulation at 12.5 cm depth, while 1.78, 1.92 and 2.27 dS/m at depth of 62.5 cm respectively. At 2.0 m watertable depth EC increased to 1.9 dS/ m, 2.2 and 3.8 dS/m at a depth of 12.5 cm, while at a depth of 62.5 cm EC reached to 1.8, 1.98 and 3.8 dS/m respectively. For free drainage EC decreased from 0.94 dS/m to 1.13 dS/m at depths of 12.5 and 62.5 cm respectively. The soil salinity was increased with rising of water table under controlled drainage and it decreased in case of free drainage. It is concluded that LEACHC is a valid model for simulation of solute transport and it is applicable to soil salinity status of Mardan SCARP.