In-Situ Measurement of Unsaturated Hydraulic Conductivity Function by Point Source Field Dripper Method Using Newly Developed Micro Irrigation Simulator for wheat Field

Abstract

Unsaturated hydraulic conductivity function (Kh) is an important soil parameter stating water transmission characteristics within the soil mass. It is essentially required in designing of drip irrigation systems. There are many laboratory and in-situ measurement techniques available for the measurement of Kh. These methods have associated limitations. Soil particle distribution curve had been also used for Kh estimation which is laborious and associated with own limitations. A point source field dripper model (PSFDM) using Wooding [1] theory was first time used by Shani et al. [2] for Kh measurement in the field. Experimental set up used earlier had great limitations of controlling dripper discharge by maintaining appropriate pressure in drip line. Hence an experimental set up (micro-irrigation simulator) was developed for in-situ measurement of Kh which simulates real field drip conditions. Experiments was conducted to measure steady state saturated fronts against 2.02, 4.04, 7.56 and 8.31 lph dripper discharges maintaining one atmospheric pressure in drip line in recently harvested wheat field. Inverse saturated radii (r-1) were plotted against water flux density q (cm hr-1).  Slope and intercept of the plotted line was worked out and Ks and α were calculated using steady state PSFD theory. Ks value was calculated as 50.03 cm/day and α as 0.1048 cm-1 using PSFD model of Shani et al. [2] and 60.00 cm/day and 0.0984 cm-1 using PSFD model of Warrick [3]. Ks value measured by using inverse auger hole method was 8.694 cm/day and by infiltrometer test 19.13 cm/day. The PSFDM is relatively new method and is useful for measuring Kh of tilled zone. Kh values are much higher than the values of Kh of untilled soil at deeper depths due to compaction. The developed experimental set up has great compatibility with PSFD theory.