Vadose Zone evolution under shifting cultivation practices in Northeast India.

Shifting cultivation is one of the old methods of farming practiced in various countries, including India, where land is cleared by slash and burn. In India, shifting cultivation, locally known as Jhum, is extensively practiced in its North-eastern states. Since using fire removes the forest land, it is said to have various implications on the vadose zone properties, along with an increase in sediment yield from runoff. The available literature on the effect of Jhum cultivation includes general studies on areas with different intensities of Jhum. Still, the Jhum sites have significant topography and geography variations, making it difficult to evaluate the effects of Jhum cultivation accurately. Therefore, to understand the impacts of Jhum in Northeastern regions in India, three Jhum sites are selected in a micro-catchment under similar topographical conditions in the Aizawl district of Mizoram state in India. Three sites represented various stages of Jhum cultivation, namely Non-Jhum land (NJL) or fallow land, Cultivated Jhum Land (CJL), and Newly Burnt Jhum land (NBJL). The Impacts of Jhum on various physicochemical properties of the vadose zone soils are reviewed thoroughly under multiple stages of Jhum. Hydraulic conductivity measured using Inversed Augur Hole Method gave maximum hydraulic conductivity at NBJL, followed by NJL and CJL. Water and sediment samples were collected from the downhill streams at selected gauging sites near the three Jhum sites. Soil samples were also collected from the selected sites at different depths viz top surface, 5 cm, and 55 cm, such that the impact of Jhum is quantified at various stages after clearing the forest land, along with variation in soil properties with depth. Laboratory analysis of the soil samples showed that Soil Organic Matter (SOM) and Soil Organic Carbon (SOC) values decreased as we moved from the surface to 55 cm below the ground at all three sites. Soil structure in all three areas was similar, with maximum percentages of medium to fine sand suggesting only minor changes due to burning. Further, pre-monsoon and post-monsoon comparison of all the soil/sediment and water quality characteristics is done. Estimation of Macro-nutrients with few micro-nutrients is also done for soil and sediment samples to study the changes in nutritional characteristics of soil at various stages of Jhum. The result of this study would help in managing the soil-water resources of the region and understanding the sustainability of this form of agriculture.