Modelling of wetting pattern under trickle source in sandy soil of Nirjuli, Arunachal Pradesh (India)

Abstract

Wetting pattern can be obtained by either direct measurement of soil wetting in field, which is site specific, or by simulation using some models. Use of numerical or analytical flow models for design purpose is considered cumbersome and impractical in many situations. Therefore, present study was undertaken to develop a model for wetting pattern under trickle source in sandy soil of Nirjuli, Arunachal Pradesh. In the present study, the drip irrigation system was operated to record observed wetting front advance (vertical and horizontal) of emitters with flow rates of 2, 4 and 10 l h⁻¹. A fixed quantity of 4 l of water was applied to the bare dry soil kept in a container of perspex sheet (1 m × 1 m × 0.9 m). The wetting front advance was observed just after irrigation and its subsequent redistribution after 1, 2, 4, 6, 9, 12, 15, 18, 24 and 48 h respectively after irrigation. Using Buckingham π theorem, a semi-empirical model was developed to simulate the wetting front pattern under trickle point source at the end of irrigation. Performance of the model just after irrigation was evaluated by comparing estimated values against observed values using F test, t test, ME and RMSE values. The redistribution of the wetting front geometry with respect to elapsed time was modelled with regression analysis using four models viz. linear, logarithmic, exponential and power. Power function was found to be the best fit for horizontal wetting front (W) as well as vertical wetting front advance (Z) based on the highest R ² value.