Transforming jhum to plantations: Effect on soil microbiological and biochemical properties in the foot hills of North Eastern Himalayas, India

Slash and burn cultivation (jhum), a major form of traditional agriculture in the hills of north eastern Himalaya has now slowly shifted towards more stable forms of land use. This land use change in the region may have direct effect on soil quality which is an important concern for sustainable land use system. Our aim was to elucidate the impact of different land use from jhum cultivation on soil biological and biochemical properties. We have assessed the impact of such changes by comparing current jhum with replacement by plantations and forests for lengths of time varying from 15 to 30 years. The conversion to plantations (teak, arecanut and rubber) and secondary forests significantly increased the soil's water holding capacity (WHC) and soil organic carbon (SOC) contents. The SOC accumulation improved the moisture storage and increased soil microbiological processes such as microbial biomass C and N (MBC and MBN), percent of MBC to SOC, basal respiration and soil enzymes (acid and alkaline phosphatase, arylsulphatase, β–glucosidase, dehydrogenase and urease). The substrate use efficiency (metabolic quotient: qCO2) under jhum (J) was 21.5%, 25.8%, 27.8%, 39.9% higher than secondary forest (F), arecanut (A), rubber (R) and teak (T) respectively in the surface soil layer (0–15 cm) indicating microbial stress due to recent disturbances. The soil quality as defined by the geometric mean (G) over the soil depths followed the order F > R > A > T > J. Principal component analysis (PCA) was useful in discriminating the importance of soil microbiological and biochemical properties for land use change. In conclusion, land use change from jhum to forest and plantations (rubber and arecanut) conserved and improved soil quality.