Soil Organic Matter Dynamics in Eurasian Steppes

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The CO_2 flux from soil surfaces in Eurasian steppes, including Kazakhstan, Ukraine and Hungary, varied widely. It was higher in some grassland ecosystems (southern Kazakhstan) than in most of the cropland. Nonetheless a rather simple relationship was obtained between the in situ annual soil respiration and bio-environmental factors (namely "humidity and SOM accumulation" and "biomass accumulation" factors). At the same time, the laboratory approach to fix decomposition rates of SOM showed an overall similarity of the rate constants within each respective ecosystem such as steppe or forest. This might be one of main reasons for an apparent success of simulation models ever established, in which several pools of organic materials are supposed primarily based on the difference in the order of decomposition rate constants.Lowering soil respiration under cropped ecosystems tended to alleviate an active degradation of SOM-related properties of soils, which was initially observed. A signific … More ant change after reclamation of natural grassland mostly appeared in the decrease of more labile fractions of SOM, such as light fraction C or C_0. In the regional scale, the value of C_0 was useful for predicting CO_2 emission. Chemozem soils seemed to be, relatively speaking, stable against changes in environmental conditions and/or land use, not like as forest ecosystems, in which accelerated decomposition of SOM was often observed after reclamation.The geostatistical analysis suggested that the overall accumulation of SOM in agro-landscape in northern Kazakhstan was primarily affected by the cumulative primary production as a result of soil moisture regime and land use/management. Such a variation caused by topography and water regime was also pointed out for Ukrainian steppe soils. The most important determinant for primary production is water availability, whereas that of decomposition is usually temperature in the steppe ecosystems investigated. Agricultural practices usually modifies soil water regime for achieving maximum crop production, followed by removal of primary production as harvest, but it does not essentially change the dynamics of SOM and/or nutrients. If the adverse effects of agricultural practices on SOM regime under steppe environment are actually limited, as suggested from different approaches, a site-specific agricultural management based on the spatial patterns of organic matter dynamics would be a suitable option in reality for harmonizing sustainable agricultural production with environmental conservation by reducing organic matter decomposition. Less