Soil and land use factors control organic carbon status and accumulation in agricultural soils of Lower Austria
Walter W. Wenzel, Olivier Duboc, Alireza Golestanifard, Christian Holzinger, K. Mayr, Johanna Reiter, Anna Schiefer
Abstract
Policies for restoring soil health and mitigating climate change require information on soil organic carbon (SOC) stocks and their spatial and temporal variation, and related sequestration potentials. Using the province of Lower Austria as environmentally diverse model region, we present a detailed analysis of SOC stocks, saturation potentials and deficits along with SOC monitoring data for the past three decades. Using the provincés soil database (sampling 1991) we estimated the saturation potential for mineral-protected C (Csat) by boundary line regression to the particle fraction <20 µm (f<20µm). Compared to published work, parameterization by Lower Austrian data yielded considerably larger Csat values which agree well with independent maximum organic C load estimates based on specific surface area. Csat is particularly small in topsoils of regions with non-calcareous igneous rock, but large on fine-textured quaternary and tertiary sediments, and weathering residuals of carbonate rock. During the past three decades, the medians of SOC in grassland topsoils (0–20 cm) increased significantly (p < 0.05) by 29.7% from 39.4 to 51.1 g kg−1, corresponding to annual accumulation rates of 0.87 Mg C ha−1. SOC in cultivated soils increased by 17.1% from 12.7 to 14.8 g kg−1 (0.20 Mg C ha−1 y−1). Because of the large initial C gap, the observed SOC accumulation is not related to Cdef but likely reflects improved soil management.