Profile distribution and edaphic controls of soil organic carbon in dominant soil orders of Chitwan, Nepal

Abstract Soil profile distribution of soil organic carbon (SOC) in different soil types provides information about the carbon (C) dynamics in terrestrial ecosystems, and is also important for understanding climate feedback mechanisms and for developing a proper farm level SOC management decision. However, there are limited studies on it when we consider soil horizons of dominant soil orders of Nepal, which mostly use a fixed depth approach rather than horizon-based approach while studying profile SOC distribution. We collected soils from master horizons (0 to 100 cm) of three dominant soil orders (Alfisols, Entisols, and Inceptisols) in Chitwan district of Nepal, to understand the controlling factors of SOC accumulation. Dominant soil order regions were identified using a soil map prepared by the National Land Use Planning Project where a pit of 1 m 3 was dug for each soil order and replicated four times. The highest SOC concentration (10.1 ± 0.6 g kg −1 ) was found in Alfisols followed by Entisols (8.8 ± 0.3 g kg −1 ) and Inceptisols (7.2 ± 8.9 g kg −1 ). Similarly, the highest SOC stock was found in the soil profile of Alfisols (200.01 ± 15.97 t ha −1 ) followed by Entisols (124.67 ± 12.20 t ha −1 ) and Inceptisols (113.27 ± 10.30 t ha −1 ) horizons. Surface (A) horizons of all three-soil order had significantly higher SOC than sub-surface (B and C) horizons. Regression analysis showed significant variability in SOC to clay content (R 2 = 0.45, p < 0.0001), sand (R 2 = 0.19, p < 0.001), and total nitrogen (N; R 2 = 0.835, p < 0.001). Principal component analysis showed that the controlling edaphic factors differ with the soil types considering SOC change in the whole soil profile. Overall, we found that soil pH, N, clay and sand contents are the major controlling factors that drive the SOC accrual in dominant soil orders of Nepal. Graphical Abstract