Relationship between concentrate feeding strategy and grassland phytodiversity on dairy farms

Permanent grassland provides various ecosystem services ranging from livestock feed provision to biodiversity preservation. With increased use of concentrate supplementation in dairy cow rations the importance of permanent grassland as the main feed resource in dairy production systems has decreased, although in Germany a large area of permanent grassland is still utilized by dairy farmers. How phytodiversity can be improved by adaptations at the production-system level other than by organic farming has rarely been examined. We hypothesize that in systems based on lower levels of concentrate feed supplementation farmers adjust their management to the different conditions of grassland sites in interaction with the distinct nutritional needs of the different animal groups in a more differentiated way. Thus, due to higher management diversity, a higher farm-level phytodiversity should be found on those farms. We examined the effect of feeding strategy (low level (LC) vs. typical regional concentrate feeding level (HC)) considering two types of farming systems (organic vs. conventional) in three grassland-dominated regions of Germany on management diversity as well as on overall species number per grassland sampling site (α diversity), per farm (γ diversity) and on the heterogeneity between the sampling sites of each farm (β diversity). The underlying sample comprised 388 vegetation surveys on permanent grassland of 28 farm pairs (HC+LC), whereof 15 were organic and 13 were conventional farm pairs. Phytodiversity indices differed significantly between Concentrate Categories or between Concentrate Categories in interaction with the Farming System. In conventional farming systems grassland phytodiversity at site and farm level (α and γ diversity, respectively) were significantly higher on LC farms than on HC farms and conventional HC farms had less high nature value plant species in their grasslands. On organic farms these parameters were comparable to the conventional LC farms for both Concentrate Categories. In the northern study region phytodiversity indices were overall smaller than in the southern and central study regions. Across regions, management diversity as expressed in the number of grass products on farm level and plant species heterogeneity between sampling sites (β diversity) were higher on LC than on HC farms irrespective of farming systems which was underlined by a significantly positive relationship. On LC farms 4.8 ± 0.9 and on HC farms 4.1 ± 1.3 grass products were produced. Our results indicate that a feeding strategy with low concentrate input is one way to improve grassland phytodiversity, especially in conventional farming systems under central European conditions.