Influence of crop rotation system on the spatial and temporal variation of the soil organic carbon budget in northern Kazakhstan

To optimize regional crop rotation systems to mitigate soil organic carbon (SOC) depletion, monitoring the spatial and temporal variation of the SOC budget is of major importance. This study evaluated the influence of crop rotation and topography on the spatial and temporal variation of the SOC budget under cereal cropping in northern Kazakhstan using a geostatistical method, predicted equations of CO₂ emission and Moderate Resolution Imaging Spectroradiometer satellite images. The study was carried out in large-scale upland fields (7,915 ha) located in Shortandy, Aqmorinskaya Oblast, from 2001 to 2005. Under the assumption that all crop residue was incorporated into the soil, average annual C input as plant residues in cereal and abandoned fields ranged from 1.0 to 1.6 Mg C ha⁻¹ year⁻¹, with higher values in wet years. Average annual CO₂ emission in the cereal fields and the fallow fields ranged from 1.0 to 1.2 Mg C ha⁻¹ year⁻¹ and from 0.7 to 0.8 Mg C ha⁻¹ year⁻¹, respectively. In relation to topography, CO₂ emission was higher on the north-facing slope than the south-facing slope, with the highest values on the higher plateau, and the average annual carbon budget ranged from -0.1 to 0.3 Mg C ha⁻¹ year⁻¹. It should be noted that all fallow fields consistently had a negative carbon budget. The 5-year carbon budget for different crop rotation systems ranged from -0.5 (fallow-based rotation) to 0.6 (wheat-based 5-year continuous cereal cropped) Mg C ha⁻¹. These results have some uncertainly because of the low predictive ability of the regression; however, the results indicated that fallow-based and barley-based crop rotation systems were depletive and conversion of the wheat-fallow system to continuous wheat cropping would sequestrate 0.1-0.3 Mg ha⁻¹ year⁻¹ of carbon into the soil.