Evaluation of soil water retention characteristics using pedotransfer functions of Alfisols in Meghalaya

Soil water retention characteristics particularly saturated hydraulic conductivity (Ks) is an important variable in a hydrological cycle. Determination of Ks in soils is a difficult and time consuming process. Hence, pedotransfer functions (PTFs) were used for estimating hydraulic properties of rice soils from six rice-growing districts namely Ri-Bhoi, Jaintia Hills, East Khasi Hills, West Khasi Hills, West Garo Hills and South Garo Hills of Meghalaya, India. Soil water retain ed (θ) at varied matric potentials (h) was measured in the laboratory and various water retention functions proposed by different researchers were fitted to the laboratory measured data. It was also observed that the h-θ relationship proposed by van Genuchten (VG) fitted better for these soils. Pedotransfer function (PTF) ‘Rosetta’ (hydrus 2D software's code or module for estimation of unsaturated zone hydraulic parameters) was used to predict VG parameters from basic soil data. The estimated parameters suggested that the soils were unique in hydraulic behaviour. It was observed that the residual soil-water content θr and saturated soil-water content θs were lower in magnitude as compared to the class values. Observed and predicted values of soil-water retention were compared to evaluate the performance of Rosetta. The coefficient of determination (R2 = 0.90) values suggested that it could predict soil-water retention in lower suction range with relatively greater accuracy. Comparatively better predictions were obtained with basic data on texture, bulk density and field capacity as an input.