Estimating Soil Hydraulic Properties Using Field Drippers

A field dripper method is proposed to estimate the soil hydraulic properties based on unsaturated hydraulic conductivity function of Gardner (1958). In this method, water is applied at a constant rate to a point on relatively level and dry soil using field drippers, which create a ponded zone. For low dripper discharges a hemispherical saturated soil geometry is most common. The area of saturated zone increases with time and approaches a constant circular area quickly. Steady state solution of two dimensional soil water flow in homogenous and isotropic soil is developed and applied for estimating unsaturated hydraulic conductivity function, which is of great importance in drip design. Other hydraulic parameter ‘α’ (an empirical constant, which is relative measure of capillary and gravity) can also be determined based on assumed relationship. It is a reliable, quick and practicable field method. A comparison of hydraulic parameters (Ks and α) measured and estimated by other methods for three soils show good agreement with field dripper method. In sandy loam soil, the proposed dripper method gives 10.5, 2.7 and 1.8 per cent higher Ks values over inverse auger hole, cylinder infiltrometer and cavity methods, respectively. In silty clay loam soil Ks values obtained by cylinder infiltrometer and inverse auger hole methods are 12.1 and 55.8 per cent lower than field dripper method. In loam soil, the values of Ks obtained by dripper and cavity method have close agreement. The values of ‘α’ estimated by field dripper method was within the range of values obtained by other workers, but was higher than the values obtained from different laboratory methods, i.e. Diffusivity method, steady state method and data generated by empirical equations.