| Summary: | Plants are constantly exposed to solar radiation. Thus, the observed raised levels of UV-radiation lead also to a raised exposure for plants. In the recent years, so-called 'non-parasitic leaf spots' (NPLS) have led to yield losses for barley of up to 40 %. It is assumed that this disease is caused by raised UV-radiation levels. For this reason a model has been developed to calculate UV-exposure within plant stands for longer periods. By use of plant-specific parameters this model can be applied for different plant types, for forests as well as for crops like barley. The model calculates the variation of irradiance due to different sun positions, and due to atmospheric parameters such as total ozone content, aerosol amount and properties, as well as clouds. The model takes into account the plant growth, which is important for annual plants like barley. As an example, the UV-exposure has been modelled for a real barley stand in southern Germany for the growing season of the year 2002. The plant-weighted UV-irradiances have been calculated on a hourly basis for 10 levels within the canopy, and from this the UV-exposure as the cumulative UV-radiation of all preceding days. Since plants have repair mechanisms for damage due to UV-radiation, additionally UV-impact was modelled by accounting mainly for UV-exposure during the most recent days under the assumption that its impact on the plant decays exponentially.
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