Evapotranspiration affects condensed tannin levels and MPP differently in four grassland mixes

Summary in the original language of the document

Dairy farming faces challenges of summer fodder scarcity and methane emissions. To address these issues, one may incorporate plants rich in condensed tannins (CT) into temporary grassland mixes. However, knowledge regarding the link between CT, milk production and climate remains limited in a field context. We conducted an experiment with four grassland mixes (grass, grass and legumes, grass and plants rich in essential oils, grass and plants rich in tannins) replicated four times over six rotations. CT content, dry matter yields, and botanical composition were analysed. We calculated milk production potential (MPP) based on nutrient analysis of the plant material and obtained potential evapotranspiration (PET) data. Results showed no CT difference across mixes in low PET rotations. However, during a high PET rotation CT contents in the tannin-rich mix were higher than the others. MPP remained stable over time for the legume mix, the mix with plants rich in essential oils, and tannins but decreased significantly for pure grass. CT content in the tannin mix was strongly correlated with Lotus corniculatus abundance. Our study suggests that plants produce the most CT during peak PET in summer, but forage production is highest during lower PET in spring. Thus, tannin rich mixes may primarily mitigate methane emissions in summer. Importantly, MPP from tannin mixes did not decrease with increasing PET, highlighting the potential protective role of condensed tannins on plants during summer drought.