The effect of the first cutting date and cutting frequency on the clover-grass stand growth and development and on the relationships between plant species were studied at the University of Helsinki in 1974—76. The second study objective was the relationships between several growth factors and the yield components of the stand. The third study area comprised the energy value changes and the photosynthetic activity of the stand during different phases of the growing season. The most rapid growth and development occurred within the temperature range of 400—500° C (∑ > 0° C). The late first cutting date increased yields most in the 2 and 3-cutting systems and least in the 4-cutting system, due to two summer cuts during the dry period of the season. Due to the regrowth ability of the species and lack of water in midsummer leading easily to dormancy there was a negative correlation between the first and the second cut and a positive correlation between the following successive cuts. The most important variables in the regression model describing DM production in the first, second, third and fourth cut were temperature sum in degree days, precipitation during the week before the previous cut, amount of precipitation between cuts and the physiological activity of the stand, respectively. The energy value of spring and autumn DM yield was higher than that of midsummer. The average photosynthetic efficiency was 0.95 % in 1974 and 0.47 % in 1975. The DM content of the yield in spring decreased until the temperature sum of 420° C (∑ > 0° C) and then increased linearly. The DM content, protein content, digestibility of DM and protein yield in the total yields were mostly influenced by the first cut if made when the slope showed either decreasing or increasing values of DM content. Otherwise a late first cutting date or low cutting frequency lowered the quality of the forage. In the mixture the spring growth of timothy ceased by the end of June and was replaced by red-clover. The regrowth of timothy ceased by the middle of July and was replaced by meadow fescue. The growth of red clover was the most uniform throughout the entire growing season
