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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]

• Pasture land had the greatest SOC, AC, and PC pools. • Pasture and garden fields had higher INV enzyme activity than undisturbed forests. • Pasture and maize + C3 land uses had the most SOC in 2–4.75 and 0.053–0.25 mm aggregates. • Physical protection proves that aggregation stabilizes soil organic carbon. • According to CMI, agricultural and horticultural operations reduced the amount of soil organic carbon storage. Deforestation and agricultural operations greatly impact soil organic carbon (SOC) and its fractions. In order to decrease carbon dioxide emissions, prevent threats to ecosystem stability, and apply efficient land use planning for sustainable soil management, it is essential to have a deep understanding of variations in soil organic carbon pools and their fractions. Soil samples were collected from six land uses of the undisturbed forest, pasture, orchard, and agricultural lands (cultivated with Oat, Maize, and three-carbon plants including wheat and soybean, which are indicated by the plant names of Oat, Maize + C3, and Maize + C3 (R) (R = rotationally)) with three replications at 0–30, 30–60, and 60–100 cm depths. The objective of this study was to evaluate the effect of land use on SOC, active carbon (AC), passive carbon (PC), dissolved organic carbon (DOC) content and pools, its fractions, carbon management index (CMI), soil respiration (SR), soil microbial biomass carbon (MBC), invertase (INV), and cellulase (CEL) enzymes activities in Dasht-e Naz region of northern Iran. Results illustrated that the different forms of organic carbon and enzyme activities were sensitive to land use change. The highest values of SOC (167.197, 39.179, 33.211 Mg ha−1), AC (24.596, 1.955, 1.637 Mg ha−1), and PC (142.6, 37.224, 31.575 Mg ha−1) pools were observed in the pasture land at all three depths. the highest value of DOC was seen in the pasture land at 0–30 and 60–100 depths and in the orchard at 30–60 cm depth. The values of SR (1.001 mg CO 2 g dry soil−1 week−1), MBC (1367.7 µg organic carbon g soil−1), and CEL enzyme activity (648.04 µg glucose g dry soil−1 24 h−1) in the undisturbed forest were significantly greater relative to other land uses in 0–30 cm depth, along with significantly higher INV enzyme activity in the pasture and the orchard lands. The largest amount of SOC in 2–4.75 and 0.053–0.25 mm aggregates in all depths was related to the pasture and Maize + C3 land use, respectively. The concept of physical protection confirms the importance of aggregation in the stabilization processes of soil organic carbon, as a physical shield against microorganism attacks. The results of CMI demonstrated that the carbon storage capacity decreased due to the agricultural and orchard lands establishment in the region. Also, the change of land use towards pasture land increased the amount of organic carbon, preventing soil degradation. [ABSTRACT FROM AUTHOR]

Different land use management practices e.g. native forest vegetation, pastures and the agricultural management practices (e.g. tillage, cropping system, crop residue mulching and fertilizer and manure application) influence the soil organic carbon pools, which has short term and long term implications on soil carbon dynamics. Field experiments were conducted in a sandy loam soil of the Indian Agricultural Research Institute, New Delhi research farm during the kharif season (July to October) of 2012 and 2013 with the objective to study the short term (2 years) impact of irrigation, crop residue mulch and nitrogen management in maize on soil organic carbon pools and to identify the best management practice in terms of Carbon Management Index (CMI). Maize (cv. HQPM 1) was grown in a split-split plot design with two levels of irrigation (irrigated and rainfed) as main factor, two levels of mulch (No mulch and wheat residue at a rate of 10 Mg/ha as mulch) as sub factor and three levels of nitrogen (0, 75 and 150 kg N/ha) as subsub factor. The results showed that total organic carbon (TOC) increased by 40.5% in irrigation treatment compared to the rainfed treatment for the 0–5 cm soil depth after 2nd year of cropping. Application of crop residue mulch significantly increased the TOC concentration by 14.9% at 0–5 cm soil depth compared to the no mulch treatment. Crop residue mulch also significantly increased carbon stratification ratio (SR) by 9.2% compared to no mulch treatment for the same depth. Nitrogen application at 150 kg/ha significantly increased TOC concentration at 0–5 cm soil depth by 22.2% and 7.8% over control and 75 kg/ha, respectively. Water stable aggregate associated carbon concentration in large macro-aggregates and micro-aggregates increased significantly by 16.7% and 11.8%, respectively due to crop residue mulching. Application of crop residue mulch resulted in significant increase in labile and non-labile pools of carbon at 0–5 cm soil depth compared to the no mulch treatment, and among the labile pools of carbon, the maximum increase was recorded in very labile (VL) pools. The Carbon Lability Index (CLI) decreased whereas Carbon Pool Index (CPI) and Carbon Management Index (CMI) increased due to irrigation and crop residue mulch application. Application of 75 kg N/ha resulted in significantly higher CMI than that of 150 kg N/ha at 0–5 and 5–15 cm soil depth. So maize may be grown under irrigated condition with wheat residue mulch at a rate of 10 Mg/ha and 75 kg N/ha to achieve higher total organic carbon pool and labile pools of carbon, better Carbon Management Index. [ABSTRACT FROM AUTHOR]

To evaluate the changes in the pool of organic carbon fractions, aggregate stability and activity of enzymes, degraded red soil was amended with three different rates (0.5, 1.0 and 2%) of oak wood biochar (W0.5, W1.0, W2.0) and bamboo biochar (B0.5, B1.0, B2.0), with control as 0%. After 372 days, the incubated soils were analyzed for total organic C (TOC), potassium permanganate oxidizable C (POXC), light fraction organic C (LFOC), water soluble organic C (WSC), hot-water extractable C (HWC) and microbial biomass C (MBC), macroaggregates (>0.25mm), dehydrogenase, β-glucosidase and urease. The highest macroaggregates, POXC, LFOC, HWC, MBC and enzyme activities were measured in the lowest rates (W0.5 and B0.5). MBC positively correlated with all labile organic C and macroaggregates, indicating that microbial activities result in mineralization of organic matter (OM) and contribute on bonding agent for macroaggregation. The C/N of the experimental soil negatively correlated with most of labile organic carbons and macroaggregates, which could be the effect of limited N availability on labile organic carbon fraction and aggregation. As compared to the control, lability index (LI) (changes in the lability of soil carbon) increased in W0.5 and B0.5 by 4 and 6%, respectively, whereas the carbon management index (CMI) (changes of the total carbon in the soil and its lability) increased by ranges of 50 to 286% in the treatments, and implies sequestration of organic C in soil. The high CMI is largely caused by high C sequestration and low lability differences between the treatments. Our results suggest that biochar application increases total organic carbon, stimulates microbial activities, in turn increases macroaggregation, and thus soil quality. [ABSTRACT FROM AUTHOR]