Deriving Equation to Estimate Movement of Water in Soil for Subsurface Drip Irrigation

Abstract

Subsurface drip irrigation is an efficient irrigation method because it applies water directly to the crop root zone, but one of the disadvantages of this method is the positive pressure which is formed in the soil at dripopening especially in fine soils where the drip discharge is larger than the soil infiltration capacity which leads to decrease the discharge rate because the positive pressure will reduce the operation pressure of the drip. In this study, water was applied to ahole surface which filled with gravel to a needed depth,than distributed from the holebottom to all direction through the soil. Wetting front was observed during water supply and redistribution periods . Eighteen laboratory experiments for watching advance of wetting front at different times, by using cuboid-shaped container, dimensions (50*50*70) cm. two side of this container are plastic sheets, soil was compacted in the container to achieve bulk density. Two soils were used in the experiments, sandy loam with initial water content (3% and 6%), discharge (0.5, 1.04 and 2.14) L/hr, and silty clay with initial water content (5% and 8.5%), discharge (0.54 and 1.08) L/hr. For the both soils (5 and 10)cm radius of gravel container with 20cm depth was used, the container have holes from bottom and side at 5cm high to water exit. The volume of water applied was 4.5 L. The study presents equation to estimate fully shape of wetting pattern,by using dimensional analysis techniques, the effective variables on wetting front movement had been transfered to dimensionless groups, and by using the (SPSS)software a relationship was found between distance from center of hole to wetting front and time for all direction.