Soil moisture management for determination of depth and space of drainages insecond cropping of paddy by using HYDRUS 2D/3D Model

Depletion of excess soil moisture from root zone is one of the objectives of the implementation of drainage systems. In this study the ability of HYDRUS 2D/3D model to soil moisture transport management for determining of depth and space of drains in second cropping of paddy fields of Sari Agricultural Sciences and Natural Resources University in For the three growing season (2014-2017) is assessed. So, two kinds of fields were constructed: Field A with subsurface drainage systems and drain depth of 0.9 m and drain spacing of 30 m and field B having drain spacing of 15 m and alternate drain depths of 90, 65 and 90 cm. Sensitivity analysis and calibration were first performed with the aim of verifying the HYDRUS model. The sensitivity analysis indicated that the software had maximum sensitivity to the saturated volumetric water content. Four scenarios were considered for field A in HYDRUS model which consist of: middle drain in 1- the depth of 40, 2- in the depth of 90, 3- two middle drains in the drain of 40 and 4- two middle drains of 65 cm. Scenario 4, 3, 2 in field B and scenario 1 showed the maximum of soil moisture depletion respectively. The maximum loss of soil moisture was observed in scenario 4 by 18.75 percent and minimum loss of soil moisture was occurred in scenario 1 by 0.22 percent. Also, evaluation of results showed that scenario 3 and scenario 4 depleted the soil moisture during the period of 2-days and 4-days, respectively earlier in respect to of first level of soil and reached to field capacity. Also, results showed that scenario 4 is the best in contrast to scenario 1 which has the worst.