Estimating S-index, unsaturated hydraulic conductivity and diffusivity through RETC in Indian Agricultural Research Institute farm

The hydraulic properties of vadoze zone like hydraulic conductivity, diffusivity and soil water retention characteristics are required to study soil water, nutrient and pollutant dynamics and their management. Surface layer of ten master profiles of Indian Agricultural Research Institute (IARI) farm, New Delhi were studied for different physicochemical and hydraulic properties. All ten master profiles were grouped under the order Inceptisol, subgroup Typic Haplustept and hyperthermic soil temperature regime. The soil water retention data were measured for all the sample layers and fitted to van Genuchten model using RETC software. The R² value of fitted curve varied between 0.98 to 0.99 with residual sum of squares from 0.001 to 0.003. The θr value varied between 0.0332 to 0.0760 cm³ cm⁻³ and the saturated water content between 0.4665 to 0.3613 cm³ cm⁻³. In the present study, α ranged between 0.0018 to 0.0164 cm⁻¹. The n value varied between 1.381 to 2.437. Combined for all profiles the prediction equation developed for K(θ) is K(θ) = 1.17×10⁶×θ^11.93 and D(θ) is D(θ) = 2.07×10⁷× θ^7.71 with R² value of 0.77 both for K(θ) and D(θ). The Sindex varied between 0.068 to 0.128. The S-index was significantly positively correlated with θr (r = 0.73*), θs (r = 0.64*), n (r = 0.97**) and significantly negatively correlated with α (r = -0.80**). The S-index value for all the 10 master profiles were more than 0.050 indicating very good physical quality for all the 10 master profiles of IARI experimental farm.