Soil wetting pattern from porous clay capsules using dimensional analysis

Introduction The majority of the world's dry lands are still farmed by small scale. In these farms, low cost simple irrigation methods are paid attention by farmers and also international development programs. Efficient traditional methods of irrigation such as buried clay pot irrigation is one of the most important methods that could be of great use on small and medium sized farms and gardens that have not been well studied in Iran. Also, the information on shape of wetted zone of soil under buried clay pot plays the great significance in design and management of this type of irrigation system for many land farms at arid and semi-arid regions on small and medium sized farms and gardens. Clay pot or porous clay capsules irrigation is able to release water in near root zone with self- regulative. Several parameters such as saturated soil hydraulic conductivity, soil porosity, water supply, pressure head and irrigation time may affect on discharging and soil wetting shape under sub-irrigation with porous clay capsule.
Materials and Methods Present research was carried out in 2014 carried out on the field of agriculture of faculty of Tarbiat Modares University, to study simulated soil wetting shape under two different type of buried porous clay capsule (GBN and GN) in calcareous soil with clay loam texture. The soil are generally deep to moderately deep with clay loam texture, ~ 17% CaCO3 (lime) , 0.44% organic matter and a moderately soil permeability. The slope in this study area is 0.5 -1.5%. The GBN and GB have different size and discharge. In this paper, wetted radius and depth of GBN (3.5 cm diameter and 12 cm height) and GN (3.5 cm diameter and 3.5 cm height) porous clay capsules as a subsurface point source were measured at 10, 25, 50, 80, 100 kPa of hydrostatic pressure by discharge-pressure automation instrument which was designed for this purpose. The soil weting shapes measured after 24 hr of irrigation with GBN and GB of buried porous clay capsule under clay loam soil texture. In order to predict the water distribution of clay capsules, several parameters such as saturated soil hydraulic conductivity, soil porosity, water supply, pressure head and irrigation time were modeled by with Buckingham theorem in dimensional analysis technique. Residual errors analysis was used to validate the simulation model.
Results Discussion According to the experimental results, the soil water distribution shape in GN and GBN clay capsules types followed a spherical trend, which is due to the low discharge of clay capsules. The analysis results of residual errors showed that the average of ME, RRMSE and R2 were 9.82, 23.78, 89.48 and 10.92, 57.97, 90.4 for GB and GBN respectively. Therefore, dimensional analysis models have good accuracy in determining the wetted radius and depth of two clay capsule types. Tese shows that developed model can be used to simulate wetting pattern under porous clay capsule irrigation system with point source of water application. Also, the results showed that wetted radius and depth of GN at 100 kPa pressure head was similar to GBN up to 50 kPa. In other hand, irrigation engineers can selected and used GN insted of GBN for places with high pressure ability. Because, the run of smaller nozzle (clay capsule of GN) is earier in related to the GBN at fileds.
Conclusion Water distribution in soil is important for the design, operation, and management of irrigation system for arid and semi-arid regions. In order to, the four equation was developed to simulate soil wetted depth and width with Buckingham theorem in dimensional analysis technique under two types of buried porous clay capsule (GBN and GN) at point source of water application. It is important to know that, The discharge of clay capsules increased with increasing pressure head and the relationship between discharge and hydrostatic pressures trend to non-linear in GB and GBN.Based on our experiment results, these equations can be used as a reliable method to predict the wetted soil shape in clay loam soil and had good accuracy for practical project to provide aids for deciding depth and intervals of porous clay capsules and designing a subsurface irrigation scheme. In othe hands, the models simulated values were following distribution not different than observed ones in two porous clay capsule types. The main conclusion drawn from the two porous clay capsule size’s is that the soil wetted shape in GN type was similar to GBN type at high pressure head. This point is important to principles of irrigation engineering and managment.