Effect of Intermittent Water Application from Trickle Source on The Water Movement and Moisture Distributionin Layered Soil

Abstract

Efficient design of trickle irrigation system depends on the shape and volume of wetted soil, which are affected by many factors. Among these factors are water application rate, soil profile type, initial soil moisture, and continuous or intermittent water application. The aim of this research is to study the effect of intermittent water application on the wetting pattern and soil moisture distribution for homogeneous and layered soils under trickle source.  Thirty experiments were conducted to monitor the advance of the wetting front in the soil profiles. Measurements of soil moisture content were also made at selected locations to evaluate the moisture distribution in soil. A rectangular box with inside dimensions of 147 cm*90 cm*5 cm was used to build the soil profile. One of the faces of the box is transparent. Two different soils were used; a sandy loam and a   silty clay loam. The soils were air dried, sieved, and packed inside the box in accordance with their apparent densities which have been measured in the field. Four types of soil profiles were built; the first was sandy loam soil, the second was silty clay loam soil, the third was (silty clay loam/ sandy loam) layered soil, and the fourth was (sandy loam/ silty clay loam) layered soil. Three water application rates were used for each soil profile. Three continuous or intermittent applications were used; continuous applications, equally intermittent applications (120 minutes ON with 120 minutes OFF), and different intermittent applications ([1]20 minutes ON with 240 minutes OFF). In addition, several cylindrical infiltration tests were conducted to describe some characteristics of each soil. Empirical relations to predict each of vertical (under trickle source) and horizontal (at soil surface) wetting front advance were found in this study. Empirical relations to predict the percentage of applied water volume in horizontal strips as a function of soil depth and in vertical strips as a function of horizontal distance from the trickle emitter were also found.    The study showed that the wetted soil volume increases as either the water application rate increases, or the intermittent application ratio increases. Also, it showed that the ratio of horizontal advance to vertical advance of wetting front increases as either the water application rate increases, or the intermittent application ratio decreases. The study demonstrated that the accumulated ratio of water application volume at a certain soil depth from trickle source increases as the intermittent application ratio decreases. Also, it demonstrated that the accumulated ratio of water application volume at a certain horizontal distance from trickle source decreases as the intermittent application ratio decreases.