Optimizing soil moisture in subsurface irrigation system based on porous clay capsule technique

Abstract 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 materials. The raw material used for making clay capsules is obtained from the calcareous soil of Nasr Abad village of Gorgan, Iran. The ratio of rice bran to calcareous soil 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 by a discharge-pressure automation instrument. The results showed a significant relationship between discharges of porous clay capsules and organic matter mixed with raw material. Also, the results show that with increasing organic matter percentage in the clay capsule component, the discharge of clay capsules increased. The relationship between discharges of G10, G15, and G20 with hydrostatic pressure is linear, and in G2, and G5, this relationship becomes non-linear. Meanwhile, the soil wetting shape followed a spherical trend due to the slow seepage of clay capsules. But the soil wetting shapes in G10, G15, and G20 were completely spherical, and in G5 and G2 trended to ellipsoid vertically. Finally, this is of significance for irrigating plants in arid and semi-arid regions.