Infiltration characteristics of lateritic vadose zones: Field experiments and modeling

Abstract

Lateritic vadose zone, mostly found in tropical humid regions, is very complex and hence behaves in a different way than other vadose zones. Until now, little is known about the impact of agricultural practices on the infiltration dynamics of such vadose zones. To this end, the present study was conceived to explore infiltration characteristics of lateritic soil-water zones by conducting 72 double-ring infiltration experiments at multiple sites considering both plot and field scales having paddy-wheat cultivation practices. Furthermore, five infiltration models, two empirical (Kostiakov and Kostiakov-Lewis) and three process-based (Philip Two-Term, Swartzendruber and Brutsaert) were fitted to the site-specific infiltration data and their performance was critically evaluated for modeling infiltration behavior of the lateritic vadose zone. Results indicated that the mean ‘quasi-steady infiltration rate’ of the Experimental Plot measured before paddy cultivation was about 0.23 ± 0.2 mm/min, which decreased by around 80% after paddy cultivation and then increases by more than 200% after wheat cultivation. Similarly, at the field scale, the ‘quasi-steady infiltration rate’ decreases by about 60% after paddy cultivation. The Swartzendruber model followed by the Brutsaert model provided the most reliable estimates of saturated hydraulic conductivity. The Swartzendruber, Brutsaert and Kostiakov-Lewis models showed a greater fitting ability in predicting ‘cumulative infiltration’ under all cultivation practices at both plot and field scales. In contrast, all the five infiltration models predicted infiltration rate with a lower accuracy than the cumulative infiltration. It is concluded that the infiltration characteristics of lateritic vadose zones are greatly influenced by cultivation practices as well as by macro-pores and low-permeability layers present in the soil profile. Given the significant field heterogeneity, future studies should explore the efficacy of other process-based infiltration models [e.g., the Smith and Parlange (1978) model, the Kutílek and Krejča model (1987), and the modified Green-Ampt models] in predicting the infiltration characteristics of lateritic terrains.