UNRAVELLING THE EFFECTS OF SHIFTING CULTIVATION ON PHYSICOCHEMICAL AND HYDRAULIC PROPERTIES OF SOIL AND WATER RESOURCES

Abstract

The aim of this study was to understand the impact of shifting cultivation on soil and water resources of the vadose zone. A micro-catchment situated in the Aizawl district of Mizoram state in Northeast India was selected for this study. Three sites were chosen in the catchment, each representing a different stage of cultivation viz 1) non-jhum land (NJL) or fallow land, 2) newly burnt jhum land (NBJL), and 3) cultivated jhum land (CJL). The study focused mainly on assessing the impacts of jhum cultivation on physicochemical and hydraulic properties of the vadose zone soil-water resources, including changes in the organic matter content, pH, nutrients level and soil texture and structure. By selecting jhum sites with similar topographical conditions, this study provides a better understanding of the effects of jhum cultivation on physicochemical properties of the local soil and water resources. To assess the effects of jhum cultivation at three different stages of jhum, soil samples were collected from multiple depths, including the top surface, 5 cm, and 55 cm of the vadose zone. Water and sediment samples were also collected from three streams flowing downstream from these three jhum sites. Findings reveal that both mean hydraulic conductivity and surface infiltration values were highest at NBJL. Furthermore, soil indices including Soil Aggregate Stability Index (SASI), Soil Sealing Index (SSI), and Forestier Index (FI) were estimated to understand the properties of surface soils and their micro and macro-nutrients availability. According to the SASI analysis, all soil samples from the jhum sites exhibited a stable soil structure. The SSI results indicated that the surface soils had no risk of thrust or erosion due to Jhum practice. The FI assessment revealed that the vadose zone soils possessed abundant nutrient reserves. Soil texture in all three areas was found almost similar, with maximum percentages of medium to fine sand and the texture varying from sandy loam to loamy sand. TOC (%) of surface samples were highest at CJL at 8.73% compared to 7.62 % at NBJL and 7.47 % at NJL. To study the seasonal variability of sediment quality, pre-monsoon, and monsoon comparison of all the stream sediment analysis was conducted. Macro and Micro-nutrients (phosphorus, potassium, calcium, magnesium, manganese, iron, sodium, and zinc) were quantified for soil and sediment samples to study the changes in their concentration at various stages of the jhum. The result of this study would help in managing the soil-water resources of the region with a better understanding of the sustainability of jhum cultivation.