Different management practices influence growth of small plants in species‐rich hay meadows through shading

Aims The intensification of grassland management can cause a loss of biodiversity via alteration of the structure and micro‐environmental conditions within the sward. The species richness of hay meadows protected within the Natura 2000 network is often endangered by high levels of fertilisation and relatedly, increased cutting frequency, which leads to decreased light availability for small plants and seedlings at ground level. The purpose of this study is to analyse how management practices and the interaction of fertilisation and cutting regime affect light distribution in grassland canopies as well as the growth of small plants. Location South Germany. Methods This was investigated by measuring the photosynthetically active radiation (PAR) and dry matter yield (DMY) of the first growth cycle over 2 years at two sites of a 5‐year‐old hay meadow trial. To calculate the relative light intensity, PAR was measured above the canopy and at ground level. Two factors, fertilisation (none, PK, NPK) and date of first cut (based on phenological stages), were manipulated. Results Our results show that the date of the first cut had no influence on light availability during the first growth cycle, whereas fertilisation decreased light availability for small plants due to a denser canopy. Fertilisation increased the DMY of the first growth cycle significantly. We show that NPK fertilisation (35 kg N, 35 kg P2O5 and 120 kg K2O ha−1 a−1) decreased both the number and proportion of small plant species. Conclusion NPK fertilisation can lead to a loss of biodiversity. These results are of relevance for the improvement and management of species‐rich hay meadows. Because of its effect on competition for light, the supply of plant‐available nitrogen is a key driver in obtaining or restoring biodiversity in species‐rich hay meadows. Therefore, careful site‐adapted fertilisation is a basic requirement in maintaining the ecological value of grassland. Intensifying grassland management can cause a loss of biodiversity via alteration of the light availability for small plants. This was investigated by measuring the photosynthetically active radiation and dry matter yield of the first growth cycle at two hay meadow sites. Our results show that NPK fertilisation decreased light availability to small plants due to a denser canopy.