Land use types and topographic position affect soil aggregation and carbon management in the mountain agro-ecosystems of the Indian Himalayas

The impacts of land use and topographic position can be evaluated through the carbon management index (CMI) that conceptualizes the carbon lability and soil aggregation. Soil aggregation patterns, carbon pools, and carbon management of the soil system not only affect the distribution of the mineral fraction of the soil but also the organic components. This study was conducted with the objectives of investigating soil carbon pools, soil aggregation, and CMI under seven land use types (dense forest, mixed forest, scrub forest, horticulture, agri-horticulture, irrigated, and rainfed cropping systems) under three topographic positions (summit, slope, and gully) in the mountain agro-ecosystem, of the Indian Himalayas. A total of 405 composite soil samples [7 land use types and 3 topographic positions and 21, 18, 33, 9, 12, 24, and 18 replications for the dense forest, mixed forest, scrub forest, horticulture, agri-horticulture, irrigated, and rainfed cropping systems, respectively] were collected for laboratory analyses. It was observed that the dense forest land use type has the highest Walkley-Black carbon (WBC), soil aggregation, total carbon (TC), and CMI values, while significantly (p < .05) lowest amount was observed with rainfed land use system. Land use type had minimum effect on nonlabile carbon (NLC), lability of carbon (LC), lability index (LI), and carbon pool index (CPI) of the agro-ecosystem. We conclude that the CMI value was in the range of similar to 31 to 88%, 24 to 82%, and 23 to 74% for summit, slope, and gully topographic positions of land use types, respectively. An average CMI was significantly (p < .05) the highest in the dense forest (similar to 48%) followed by scrub forest and mixed forest (similar to 43 and 40%, respectively). Meanwhile, irrigated land use had significant (p < .05) lowest CMI (similar to 25%). Overall, results indicated that land use types and topographic positions significantly influenced with lability of the carbon. These results suggest that restoration of degraded rainfed and irrigated agriculture lands to agri-horticulture, dense, mixed, and scrub forest lands decrease in intensity of land use could increase carbon and soil aggregation sustainability in the study area as well as other similar mountainous agro-ecosystems.