Nitrogen balance of hay meadows with and without fertilization

In a paired field experiment in Oensingen (Switzerland), a fertilised and an unfertilised meadow had been established in 2001 after conversion from arable rotation. Beside the carbon budget, also the entire nitrogen budget of the two grassland fields with all input and output processes have been measured since 2006. Although the nitrogen input to the unfertilised field was much smaller, the harvest yield was only slightly reduced. The calculation of the total nitrogen balance over two years showed an accumulation for the fertilised and a likely loss for the unfertilised field, which are to be localised in the soil organic matter. A fully analogous behaviour was also observed for the carbon balance of the two fields. Thus the fertilised meadow acts as a net sink for greenhouse gases – in contrast to the unfertilised meadow – but in turn it represents a larger source of the reactive nitrogen compounds like ammonia and nitrogen monoxide that contribute to air pollution problems.