Water stress due to increased intra-annual precipitation variability reduced forage yield but raised forage quality of a temperate grassland

Abstract

Due to climate change an increase in the intra-annual precipitation variability including extreme drought and heavy rainfall events is predicted to impact major ecosystem processes. Evidence suggests that crop and forage production will be affected by altered climate variability. Due to the growing human population and rising demand for high quality animal feed it is necessary to determine the consequence of increased precipitation variability on forage yield and quality in order to adapt or implement compensation strategies against possible negative effects.Here, we present data from a field experiment in which a temperate European grassland was subjected to altered intra-annual precipitation variability (low, medium, high) in interaction with management strategies namely fertilization and alteration of harvest date (delay by 10 days). We measured forage yield and root length, quantified parameters of forage quality (crude protein, crude fiber, crude ash, crude fat, sugar, neutral detergent fiber (NDF), acid detergent fiber (ADF), in vitro gas production) and estimated relative feed value, net energy for lactation and metabolizable energy. Additionally, we tested the influence of seasonality of extreme weather events on the responsiveness of forage yield and quality to management strategies.Increased intra-annual precipitation variability decreased forage yield of the grassland. Furthermore, the proportion of functional groups was altered toward less grass and more forb biomass with amplified precipitation variability. Increased crude protein content and reduced fiber content (crude fiber, NDF, ADF) with increasing precipitation variability improved the relative feed values. Crude protein content was enhanced by fertilization during drought but reduced by delayed harvest after the drought period. Fertilization reduced losses in grassland annual yield caused by extreme precipitation. Management strategies proved less effective if precipitation variability occurred later in the season than earlier in the season.A nitrogen dilution effect (decreased plant nitrogen concentration with increasing shoot biomass) likely influenced the grassland crude protein contents under altered precipitation regimes and might have masked possible effects of precipitation variability on plant nitrogen and therefore on quality of grassland species. Nevertheless, alterations in the plant community composition and plant senescence seem to be the main drivers of forage quality change. Fertilization during drought periods and harvest delay after drought periods were only partially successful as management strategies to sustain forage production in more extreme precipitation regimes of the future. Further strategies need to be developed that acknowledge the shift in plant species compositions as the main driver of changes in forage quality in the face of changing precipitation patterns.