Optimizing Soil Moisture in Subsurface Irrigation System Based on Porous Clay Capsule Technique

Water, a limited resource in most parts of the world, has always been a threat to arid and semi-arid zones. Using the sub-irrigation method with the clay capsule technique is one of the most practical strategies for conserving water and reducing water consumption in arid and semi-arid areas. A clay capsule is one of the porous pipes in a sub-irrigation system that can release water near the root zone. This paper has attempted to improve the physical and hydraulic properties of clay capsules based on changing the percentage of organic matter in the raw material (G0). The raw material used in making clay capsules is obtained from the calcareous soil of Nasr Abad village of Gorgan, Iran. The ratio of rice bran husk flour to G0 as improving hydraulic properties was 1:2, 1:5, 1: 10, 1:15, and 1:20 (kg of rice bran to kg of air-dried soil). The produced clay capsules were named G2, G5, G10, G15, and G20 respectively. The water discharge and soil water distribution of clay capsules were measured at 10, 25, 50, 80, and 100 kPa of hydrostatic pressures with a discharge-pressure automation instrument. The findings revealed a positive and significant relationship between increasing organic matter levels and the discharge of porous clay capsules. Unlike in G2 and G5, the relationship between discharges and hydrostatic pressure is linear in G10, G15, and G20. Meanwhile, the soil wetting shape followed a spherical trend due to the slow seepage of clay capsules. However, the soil-wetting shapes in G10, G15, and G20 were spherical and trended to vertical ellipsoids in G5 and G2. This method is of high importance for irrigating plants, especially in arid and semi-arid regions, and can efficiently manage the water shortage problem.