Red clover has a fundamental role in organic plant and dairy production. This research project comprises of three studies focusing on yield production of red clover-grass leys, prediction of the red clover content of red clover-grass leys on a farm level, and in laboratory as a research method, and improving accuracy of energy and protein values of red clover in organic milk production. The first study aims at improving persistency of red clover-grass leys. This will be studied with special emphasis on plant physiological and canopy structure effects on yield production, resistance to pathogens and overwintering of red clover-grass leys. Best-fit varieties of red clover will be identified with help of a biadditive model based on variety tests all over Finland. Whether resistance of pathogens is affected by possible changes in pathogen strains in clover-grass canopies of different age, will be studied with molecular biological methods. Means of biological control of the pathogens will also be studied. The second study aims at 1) finding out the extent of variation in the quality and quantity of the yield and extent of biolocical fixation of red clover-grass swards, 2) finding out the soil properties affecting the variation and how these parameters could be controlled, 3) developing mehtods to estimate the clover content of the ley on farm and laboratory. Experiments will be carried out at two experimental sites with spatial variation technique. The third study aims at 1) developing laboratory methods for evaluating the energy value of red clover for practical purposes, 2) refining the red clover growth model to improve the harvesting time service provided by http://www.agronet.fi/artturi 3) studying factors that affect intake of red clover and supply of amino acids and energy from red clover 4) more reliable energy and protein values of red clover for practical purposes and 5) recommendations for supplementary feeding of dairy cows fed red clover diets under organic conditions. The laboratory methods (in vitro cellulase, gas production, NIR) for evaluating energy value of red clover will be tested against in vivo data obtained with sheep as a model animal. Rumen metabolism of feed nutrients will be studied using dairy cows fitted with rumen cannulas. The flow of dietary constituents from the rumen will be measured using omasal sampling technique and digesta flow markers. The microbial flow will be measured in reference to 15N as a microbial marker.