Effects of agronomic practices on the soil carbon storage potential in arable farming in Austria

Abstract

According to the Kyoto-Protocol for carbon dioxide mitigation the direct human induced sequestration potential of carbon in agricultural soils may in the future be included for calculating net changes in greenhouse gas emissions. Therefore we used long-term experiments on arable land in Austria differing strongly in climate and soil conditions to explore the effects of agronomic practices on changes in soil organic carbon content. Optimal mineral N fertilizer input increased the carbon stocks on an average to 2.1 t ha⁻¹compared with no N fertilization in a 36 years period. Additional farm yard manure application (10 t ha⁻¹ y⁻¹) enhanced carbon storage to about 5.6 t ha⁻¹ after 21 years. Site-specific influences must be considered. Losses of 2.4 t carbon per ha were caused by additional irrigation of sugar beet and maize in a rotation with cereals in a 21 years period. The incorporation of all crop residues resulted in an increase of 3.4 t ha⁻¹ organic carbon in topsoil after 17 years. In the uppermost soil layer (0–10 cm) minimum and reduced tillage treatment enhanced carbon stocks to about 4.7 t ha⁻¹ and 3.2 t ha⁻¹ compared to conventional soil management within a decade. Based on these results, only a limited soil carbon sequestration potential can be inferred: Manuring and incorporation of crop residues are well-proven practices on arable land and therefore no additional human induced carbon sequestration might be achieved. The adoption of minimum tillage on Phaeozems, Chernozems and Kastanozems could, roughly calculated, result in a supplementary carbon storage of about 0.6% of the entire present annual carbon dioxide emission in Austria. However, the storage of carbon in topsoil means only a mid-term sequestration. By changing practices in short-terms, these amounts of carbon might be a source of additional carbon dioxide in the future.