Impact of long-term nutrient supply on plant species diversity in grassland: an experimental approach on conventionally used pastures

Abstract

The research was initiated to determine the impact of long-term (16 years) differentiated N, P, K supply on the floristic diversity of conventionally used pastures classified as Lolio-Cynosuretum. At four different sites the factors N supply (0, 160 and 320 kg N ha^-1 a^-1), P supply (0.26 and 52 kg P ha^-1 a-1) and K supply (0.66 and 133 kg K ha^-1 a^-1) were tested in 27 different supply combinations in a factorial design with three replicates. Dry matter (DM) yields of the 1st cut, soil chemical values (pH, P and K concentrations) and the number of species were determined.
Site-independent N fertilisation had the largest influence on the diversity, reducing the number of species as a consequence of light competition due to an increase in biomass productivity as well as a decrease in soil pH-levels. Mostly, also the factor K had a significant effect. Recorded species numbers ranged from 7 up to 35 species 25 m^-2. On most sites a ‘humpback relationship’ (unimodal relationship) could be observed between productivity and the species number, with maximum species numbers reached with first cut yield levels between 2.5 and 3.5 t DM ha^-1. The humpback relationship between productivity and species richness however was not a curve, but an envelope filled with points, indicating that besides productivity also other factors influence the attained species number. In this view the highest number of species were recorded in case of a co-limitation of N and K, indicated by a N:K ratio in the above ground biomass between 1 and 1.5, as well as soil pH-levels between 4.5 and 5.5.