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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]

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]