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Peak oil is forcing our society to shift from fossil to renewable resources. However, such renewable resources are also scarce, and they too must be used in the most efficient and sustainable way possible. Biorefining is a concept that represents both resource efficiency and sustainability. This approach initiates a cascade use, which means food and feed production before material use, and an energy-related use at the end of the value-added chain. However, sustainability should already start in the fields, on the agricultural side, where the industrially-used biomass is produced. Therefore, the aim of my doctoral thesis is to analyse the sustainable feedstock supply for biorefineries. In contrast to most studies on biorefineries, I focus on the sustainable provision of feedstock and not on the bioengineering processing of whatever feedstock is available. Grasslands provide a high biomass potential. They are often inefficiently used, so a new utilisation concept based on the biorefining approach can increase the added value from grasslands. Fodder legumes from temporary and permanent grasslands were chosen for this study. Previous research shows that they are a promising feedstock for industrial uses, and their positive environmental impact is an important byproduct to promote sustainable agricultural production systems. Green Biorefineries are a class of biorefineries that use fresh green biomass, such as grasses or fodder legumes, as feedstock. After fractionation, an organic solution (press juice) forms; this is used for the production of organic acids, chemicals and extracts, as well as fertilisers. A fibre component (press cake) is also created to produce feed, biomaterials and biogas. This thesis examines a specific value chain, using alfalfa and clover/grass as feedstock and generating lactic acid and one type of cattle feed from it. The research question is if biomass production needs to be adapted for the utilisation of fodder legumes in the Green Biorefinery approach. I have attempted to give a holistic analysis of cultivation, processing and utilisation of two specific grassland crops. Field trials with alfalfa and clover/grass at different study sites were carried out to obtain information on biomass quality and quantity depending on the crop, study site and harvest time. The fresh biomass was fractionated with a screw press and the composition of press juices and cakes was analysed. Fermentation experiments took place to determine the usability of press juices for lactic acid production. The harvest time is not of high importance for the quality of press juices as a fermentation medium. For permanent grasslands, late cuts, often needed for reasons of nature conservation, are possible without a major influence on feedstock quality. The press cakes were silaged for feed-value determination. Following evidence that both intermediate products are suitable feedstocks in the Green Biorefinery approach, I developed a cost-benefit analysis, comparing different production scenarios on a farm. Two standard crop… Advisors/Committee Members: Wiggering, Hubert (advisor).