Methodological approaches and baseline of ground-based monitoring of soil organic carbon content and storage in arable light chestnut soils (kastanozems), volgograd region

Numerical values of baseline evaluations of soil organic carbon (SOC) content, storages, soil bulk density, characteristics of their spatial variability and differential vertical distribution within layer 0–40 cm characterized the whole humus layer for the monitoring test polygon at the territory of experimental station “Oroshaemaya” in Volgograd Region (Russia) at the south of Volga Upland are submitted. Mentioned indicators characterize arable land in crop rotations on rain-fed and irrigated soils and 50-year fallow at 7 dynamic plots with loamic agrochestnut soils and accumulative-carbonate agrozems formed from pale-brown sandy loams (Haplic Kastanozems (Loamic, Aric)). To select monitoring objects, a multi-time soil line coefficient map and a retrospective analysis of remote sensing data for 40 years and soil survey were used. Each dynamic plot 30 × 30 m includes 9 individual points with differential soil sampling by depth from thin 5- or 10-cm layers. Variation coefficient in space increases from 5–10 to 30–40% due to increasing of the layer depth. On arable land, a uniform vertical distribution of SOC content within arable topsoil is justified. On fallow, accumulative type of vertical distribution SOC content with maximum near surface in light-humus postagrogenic horizon with sod is regenerated. Experimental evaluations of SOC content and storages are comparable with existing materials on light-chestnut soils at interfluve of Volga and Don. The selected objects are representative for monitoring. For the 0-30 cm layer, the minimum significant difference in SOC storages averages 3.4 t/ha with a variation from 2.7 to 4.6 t/ha. The comparison of SOC stocks of different dynamic plots is significantly influenced by the vertical distribution of soil bulk density, which depends on anthropogenic impact.