Increasing demand for food, feed and bioenergy provokes an increased demand for cropland. This leads to intensification of grassland and conversion of e.g. grassland to cropland. By converting grassland to cropland the enhanced mineralization of organic soil matter leads to high emissions of the greenhouse gases CO2 and, in a much lower extent, N2O. the other way around, if cropland is converted to grassland a long-term carbon sink is established that accumulates high amounts of carbon. Nevertheless the conversion of cropland to grassland cannot compensate GHG emissions caused by conversion of grassland to cropland. Due to the soil structure and characteristics C-sequestration in the soil is higher for grassland than for cropland and within the grasslands it is substantially higher for old, humus-rich and boggy sites (e.g. fens or peatbogs) than for young grassland on mineral soils (Schuler et al. 2014). GHG emissions from converting grassland to cropland are more than 12.5 times per areaunit higher for organic than for mineral soils (own calculations after UBA 2014). Avoiding conversion of grassland into cropland avoids on average 10 tCO2-equ/ha*a considering a time-period of ten years (Osterburg et al. 2009).
Purpose of the Technology: The aim of grassland preservation is to avoid/reduce GHG emissions and maintain and develop a carbon sink. Furthermore, grassland habitats have higher biodiversity than croplands and are, in general, less intensively managed. Thus, inputs of fertilizers and pesticides are lower, which is beneficial for water quality regardless of how intensively the grassland is managed. Unlike cropland, grassland is not ploughed or harrowed annually, resulting in better soil protection and a lower risk of erosion; the latter because of the year-round vegetation cover.
Establishment / maintenance activities and inputs: During a research project, the interdependencies between climate change and land use were analysed, and different strategies for sustainable land use management in Germany were modelled. Relevant land use measures which can contribute to the reduction of GHG emissions were evaluated with respect to climate mitigation, bioenergy by biomass, environmental and biodiversity protection (www.cc-landstrad.de). Grassland preservation is one land use practice which showed multiple advantages compared to cropland (after conversion from pasture): these were higher carbon sequestration and lower GHG emissions, better soil protection against erosion, and improved water storage capacity. The disadvantages and thus trade-off of grassland preservation are foregoing production of high-yielding cash crops, higher labour demand per hectare, and lower agricultural income. However, given the importance of preserving carbon stocks accumulated under grassland, the existing pastures should be retained wherever possible. The preservation of grassland is recommended everywhere, but especially for areas with organic soils/peaty soils - as high GHG emissions are the consequence otherwise.
