Determination of evaporativity and prediction of in situ estimated soil water properties

A field study on evaporativity and hydraulic properties of soil at low (December) to high (April-May) evaporative demand periods was carried out in two soils viz. Aeric Haplaquept and Typic Paleustalf, dominant in Deras command area, Orissa. Water release capacity of Aeric Haplaquept was maximum. Total water loss (WL) was strongly related with cumulative pan evaporation (CPE) and varied from 1.68 to 1.82 times with soil type. The cumulative evaporation (CE) was related linearly with square root of time. The flux was 24 to 69 per cent higher in Aeric Haplaquept than Typic Paleustalf. Field estimated hydraulic conductivity, K(θ) and soil water diffusivity, D(θ) showed exponential increase with time and were 2 to 22 and 3 to 12 times higher in Typic Paleustalf than in Aeric Haplaquept. Both K(θ) and D(θ) followed exponential relationship of the form K(θ) = K_se^{β(θ−θ_s)}, and D(θ) = αe^βθ, where K_S was hydraulic conductivity at saturation (θ_s), θ as soil moisture at a particular pressure head and ‘β’ and ‘α’ were constants.