An experimental investigation to characterise soil macroporosity under different land use and land covers of northeast India

Abstract

Saturated macropore flow is the dominant hydrological process in tropical and subtropical hilly watersheds of northeast India. The process of infiltration into saturated macroporous soils is primarily controlled by size, network, density, connectivity, saturation of surrounding soil matrix, and depthwise distribution of macropores. To understand the effects of local land use, land cover and management practices on soil macroporosity, colour dye infiltration experiments were conducted with ten soil columns (25 × 25 × 50 cm) collected from different watersheds of the region under similar soil and agro-climatic zones. The sampling sites included two undisturbed forested hillslopes, two conventionally cultivated paddy fields, two forest lands abandoned after Jhum cultivation, and two paddy fields, one pineapple plot and one banana plot presently under active cultivation stage of the Jhum cycle. Digital image analyses of the obtained dye patterns showed that the infiltration patterns differed significantly for different sites with varying land use, land cover, and cultivation practices. Undisturbed forest soils showed high degree of soil macroporosity throughout the soil profile, paddy fields revealed sealing of macropores at the topsoil due to hard pan formation, and Jhum cultivated plots showed disconnected subsoil macropores. The important parameters related to soil macropores such as maximum and average size of macropores, number of active macropores, and depthwise distribution of macropores were estimated to characterise the soil macroporosity for the sites. These experimentally derived quantitative data of soil macroporosity can have wide range of applications in the region such as water quality monitoring and groundwater pollution assessment due to preferential leaching of solutes and pesticides, study of soil structural properties and infiltration behaviour of soils, investigation of flash floods in rivers, and hydrological modelling of the watersheds.

Hydrological Modelling Using a Rainfall Simulator over an Experimental Hillslope Plot

“…The developed model framework is based on the physical processes on the hillslopes, where topmost surface layer interacts with the rainfall. At a hillslope site, surface runoff can be generated by any of three (1) infiltration excess; (2) saturation excess; or (3) variable source area processes [4]. If the soil is saturated, then saturation excess overland flow or retention excess flow occurs from the vegetated hillslope areas and the agriculture fields, most common near the toe of the slopes where the accumulated water from the entire hillslopes is enormous in volume [30].…”

“…It is important to quantify soil macroporosity and trace the dominating flow paths within continuous soil macropores to interpret the underlying flow mechanisms. The experimentally-derived quantitative data of soil macroporosity can have wide range of applications in various study domains such as water quality monitoring and groundwater pollution assessment due to preferential leaching of solutes and pesticides, study of soil structural properties and infiltration behavior of soils, investigation of flash floods in rivers, and hydrological modelling of the watersheds [4]. To understand the flow behavior of infiltrated water in active macropore structures of saturated undisturbed soil columns, dye tracing experiments and subsequent digital image processing exercises were carried out for the experimental plot in the present study.…”

An insight into the runoff generation processes in wet sub-tropics: Field evidences from a vegetated hillslope plot

“…Soil bulk density and saturated hydraulic conductivity of homogeneous soil matrix were in the range of 1.095-1.245 g/cc and 37-70 mm/h, respectively. Dye staining experiments conducted with the soil samples of the experimental plot indicated the presence of dense and well connected network of small diameter (1-2 mm) soil macropores (Shougrakpam et al, 2010). Therefore, very high infiltration rate, predominantly through the preferential pathways of the hillslope soil, was anticipated (Sarkar et al, 2008b).…”

Effects of a deep-rooted crop and soil amended with charcoal on spatial and temporal runoff patterns in a degrading tropical highland watershed

“…For example, several studies reported that land use change from natural vegetation to agricultural lands increased overland flow during the rainy monsoon phase and reduced baseflow during the dry phase in this region (Bewket and Sterk, 2005;Feoli et al, 2002;Taddese, 2001;Zeleke, 2000). In other countries as well, clearing of forests resulted in decreased infiltration rates and lower percolation to the sub-soils (Hanson et al, 2004;Mendoza and Steenhuis, 2002;Nyberg et al, 2012;Shougrakpam et al, 2010). Identification of the dominant runoff mechanism in relation to not only topography but also land use in the Ethiopian highlands is therefore essential for the development of effective soil and water conservation methods in this region.…”