Influence of drought stress on nutritive value of perennial forage legumes

In the next decades, forage legumes are likely to become more important. However, predicted climate change may increase the risk of droughts and thus influence their agricultural performance. Decreases in yield due to water shortage are well documented, while influences on nutritive values are inconsistent. Therefore, we examined the effects of drought on crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and water-soluble carbohydrates (WSC) of six legumes, birdsfoot trefoil (Lotus corniculatus L.); marsh birdsfoot trefoil (Lotus uliginosus Schkuhr); black medic (Medicago lupulina L.); yellow alfalfa (Medicago falcata L.); sainfoin (Onobrychis viciifolia Scop.) and white clover (Trifolium repens L.) in monoculture and in mixture with perennial ryegrass (Lolium perenne L.) in a container experiment in a vegetation hall. Moderate and strong drought stress was applied during three periods in two years. Mean volumetric soil water content at the end of the moderate drought stress period was 11 vol. % and 6 vol. % under strong stress. The effect of drought on nutritive values was considerably less pronounced than on yield. While the impact of moderate stress on nutritive quality was negligible, we found decreases in CP, NDF and ADF and increases in WSC under strong stress. This may indicate that water scarcity could even increase fodder quality and digestibility. However, the choice of legume species and stand (monoculture or mixture) had stronger effects on nutritive values than drought. We conclude that the reaction of temporary drought on nutritive values seems to be less important for the selection of suitable forage legumes species than other agronomic properties under conditions of climate change.