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• The agri-horticulture (AH) system exhibited the highest Carbon management index (CMI). • CMI increased at higher altitude in dry temperate Himalayas. • Passive carbon pool was higher under AH system than agriculture (A) by 16.2 %. • The highest Lability index was reported in A indicating lower stability than AH. Globally, land use management consistently changes the dynamics of labile and recalcitrant (non-labile) soil organic carbon (SOC) fractions. However, the effects vary depending on altitude, soils and management practices. The dry temperate north-western Himalayan region is characterized by the presence of diverse land use systems, however the comparison of these SOC fractions across various land use regimes is not well-documented in the area. This study reported the differences in labile and non-labile SOC fractions under the major land-use systems viz., Agriculture (A), Horticulture (H), Agri-horticulture (AH) and Grass fallow (OF) land in various soil-depth classes (0–20, 20–40 and 40–60 cm) along three altitudinal ranges i.e., 2200–2500, 2500–2800 and 2800–3100 m above mean sea level (m. a.m.s.l.) across the dry temperate region of north-western Himalayas. The lability index and carbon management index of the soils were determined using these fractions. The analysis affirmed the highest accumulation of active fractions viz., very-labile (2.66 mg g−1), and labile C fraction (2.55 mg g−1) under AH, while the highest recalcitrant fractions i.e., less-labile (3.34 mg g−1) and non-labile C fraction (7.46 mg g−1) was documented under H. Moreover, the Carbon Management Index (CMI) followed the order of AH > A > H > OF. All the SOC fractions, pools and CMI significantly increased with increase in altitude but declined at lower soil depths. The Pearson correlation analysis revealed that the CMI was positively correlated with the active C fractions i.e. C frac 1 (r = 0.96; p < 0.05) and C frac 2 (r = 0.9; p < 0.05). The higher active carbon pool and CMI (6.9–16 % and 4.1–15.7 % higher, respectively) under the AH may be due to the greater organic matter inputs to the soil under the agri-horticulture land use system. The findings of this study suggest that the soil can be managed sustainably by the adoption of stable land use systems such as agri-horticulture (owing to their higher CMI values) in the highly fragile dry temperate ecosystem of the north-western Himalayas. [ABSTRACT FROM AUTHOR]

Abstract 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: q CO 2) 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. Highlights • SOC and WHC increased from jhum to rubber, arecanut and forest. • MBC and MBN were higher under forest, rubber and arecanut than teak and jhum. • The q CO 2 was highest under jhum for the surface soil layer. • PCA analysis was helpful in determining the higher soil quality under forest, rubber and arecanut than teak and jhum land use. [ABSTRACT FROM AUTHOR]

• Natural factors override land-use impact on streams in the Himalayas. • Effects of 30–40% deforestation of mountain catchments propagate downstream. • Land use in the Himalayas affects streams over a dozen kilometers in the piedmont. • Erosion control in the Himalayas can reduce the flood hazard in the piedmont. Three pairs of small, fourth- to sixth-order catchments (approximately 5–80 km2), draining the margin of the Darjeeling Himalayas into the piedmont, were selected for a comparison of the land-use impact on the morphology and sedimentology of their stream channels. Each pair experienced similar annual rainfall and comprised similar metamorphic bedrock, steep topography, and brown soils; the members of each pair contrast with respect to their land-use structure as they comprise large forest cover (forest >90%) and a significant contribution of agricultural land with tea plantations (forest <63%), respectively. A set of rainfall, cross-sectional, and sediment data were collected for the characterization of the stream channels. The obtained results revealed that, under extreme rainfall and high denudation rates as well as frequent flash floods, the geomorphic response to land-use changes involving agricultural expansion at the expense of forest cover was less pronounced in the mountain channels than in the piedmont. Significant differences between the studied pairs of mountain streams draining forested and agricultural catchments were observed only at bankfull width and baseflow depth in fourth-order streams and baseflow depth in fifth-order streams. Local environmental factors such as bedrock channel boundaries, steep topography, high material supply to river networks, and selective sediment mobilization during extreme rainfall and floods override the effects of land use and exert dominant control over stream channels in mountain catchments. However, the effects of agricultural activity in mountains are propagated downstream. In the agricultural catchment in the piedmont, a local rapid decrease in river slope and an increase in water infiltration into alluvia facilitates the deposition of eroded material. In addition, the stream in the agricultural catchment exhibited a rise in the riverbed with the expansion of a braided channel over a dozen kilometers below the Himalayan front in the piedmont, while the streams in the forested catchment revealed a distinct tendency towards incision. The present-day channel morphologies and sediment patterns observed in forested catchments are most likely similar to those that existed in the studied rivers prior to the development of tea plantations and settlements in the mid-19th century. [ABSTRACT FROM AUTHOR]

Large-scale land degradation occurs in the foothill Himalayas mainly because of soil erosion, accelerated by tillage and poor management practices in agricultural lands and encroachment of land under forest cover. Land use exerts both direct (through C additions) and indirect (through its impact on soil erosion) influence on soil carbon. Partitioning of Total Carbon (TC) in organic and inorganic forms in degraded soils was studied, and compared these with soils under agriculture, horticulture and forest systems. Highest Total Organic Carbon (TOC) was recorded in forest soils followed by horticultural systems, whereas the least was observed in degraded and agricultural systems while Inorganic Carbon (IC) decreased in the sequence of: degraded lands > forest > agriculture ≥ horticulture. TOC stocks in the upper half-a-meter layer were 163.9 Mg ha−1 in forest soils followed by horticulture (144.7 Mg ha−1) while in case of TC, the degraded lands closely followed forest soils. The contribution of IC to TC was about 39% in degraded lands, which was about twice that of its contribution in forest soils. TOC decreased with soil depth whereas IC increased with depth. The increase in IC with depth was minor for agricultural and horticultural soils, whereas it was about 84% for degraded and about 61% for forest soils. Our study highlights the impact of erosion on dynamics of soil carbon and its partitioning and suggests the need to promote better carbon sequestering land use systems towards conservation of top carbon rich soil and promoting sustainability in hill ecosystems particularly in Himalayas. • Total carbon was partitioned into organic and inorganic forms. • Highest TOC was recorded in forest soils, whereas maximum IC was in degraded. • IC was 39% of the TC in degraded lands, which was twice that of in forest soils. • Degraded soils were at par with agricultural soils with respect to TOC. • Increase in IC carbon with depth was 84% for degraded lands. [ABSTRACT FROM AUTHOR]