" Simulation of soil wetting pattern with subsurface drip irrigation from line source D.K. Singh a, *, T.B.S. Rajput b , D.K. Singh b , H.S. Sikarwar c , R.N. Sahoo d , T. Ahmad c a Irrigation and Drainage Engineering Division, Central Institute of Agricultural Engineering, Bhopal 462 038, Madhya Pradesh, India b Water Technology Center, Indian Agricultural Research Institute (IARI), New Delhi 110 012, India c Indian Agricultural Statistics Research Institute, New Delhi 110 012, India d Division of Agricultural Physics, IARI, New Delhi 110 012, India 1. Introduction One of the important aspects of planning and management of subsurface drip irrigation (SDI) system is soil moisture movement pattern under it. It plays the great significance in deciding depth of lateral placement below soil surface, emitter spacing and system pressure for delivering required amount of water to the plant. Wetting pattern can be obtained by either direct measurement of soil wetting in field, which is site- specific, or by simulation using some models. In most of models the Richards equation governing water flow under unsaturated flow conditions have been used to simulate soil water matric potential or water content distribution in wetted soil. The hydraulic conductivity in unsaturated flow equations is highly nonlinear. It depends on soil water matric potential, which is transferred to soil water content using water retention function. It displays high spatial variability (Warrick and Nielson, 1980). Numerical and analytical methods have been used to solve unsaturated flow equations. Detailed information on hydraulic properties of soil are lacking and make it difficult to define it for field soils as well as expensive and time consuming. Also, ill-defined and complex agricultural water management 83 (2006) 130–134 article info Article history: Accepted 15 November 2005 Published on line 27 December 2005 Keywords: Subsurface drip irrigation Dimensional analysis Model efficiency Simulation model Wetting pattern abstract The information on depths and widths of wetted zone of soil under subsurface application of water plays the great significance in design and management of subsurface drip irrigation (SDI) system for delivering required amount of water and chemical to the plant. A simulation model was developed using semi-empirical approach and dimensional analysis method for determining geometry of wetted soil zone under line sources of water application placed below the soil surface. The predicted values of wetted depth and width were compared with those obtained through field experiments conducted under sandy loam soil. Experimenta- tion included determination of maximum depths and widths of wetted zone after 0.5, 1, 2, 3, 5, and 7 h of water application under laterals, porous pipes, and drip tape placed at 0.05, 0.10 and 0.15 m depths below soil surface. Statistical analysis revealed that there was no significant difference between predicted and observed values of wetted width and depth. The effect of discharge, depths of placement of lateral and duration of water application on wetted width and depth were similar for predicted and observed values. Predictability of model was expressed in terms of model efficiency, which was estimated as 96.4 and 98.4%, respectively, for prediction of wetted width and depth. This shows that developed model can be used to simulate wetting pattern under SDI system with line source of water application. # 2005 Elsevier B.V. All rights reserved. * Corresponding author. E-mail addresses: dksingh@ciae.res.in, dharmendradksingh@rediffmail.com (D.K. Singh). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/agwat 0378-3774/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2005.11.002