Anim. Prod. Aust. 2002 Vol. 24: 249-252 249. HERBAGE MASS PRODUCTION OF GRASS-WHITE CLOVER IN COMPARISON TO ALL-GRASS PASTURE A.T. TESFA A , P. VIRKAJÄRVI B and M .TUORI A A Department of Animal Science, University of Helsinki, P.O. Box 28, FIN-00014 Finland B Agricultural Research Centre, North Savo Research Station, Halolantie 31 A, 71750, Maaninka, Finland SUMMARY Grass-white clover sward (GWC) was compared to all grass swards (AG) in terms of its herbage mass (HM) production (kg DM ha -1 ) and animal performance. The GWC sward received 40 and AG sward 106 kg N ha -1 in two applications. Herbage mass (pre-grazing) and sward height (pre- and post grazing) was measured. The grazing season was divided in to 3 periods. Twelve autumn calving cows were turned to pasture on June 6 th and grazed until August 7 th . The cows were given 5 kg of barley- oats (1:1) mixture with 250 g of mineral supplement cow -1 d -1 . The GWC had higher herbage mass (HM) compared to AG. The live herbage mass (LHM) of GWC sward contained 13.3 % white clover without strong seasonal trends and meadow fescue made largest contribution of the sward. Towards the end of the experiment, couch grass (Elymus repens (L.) Gould) made the highest contribution in AG sward. The content of dicotylenodous weeds in AG sward was only half of that in GWC sward. AG sward had higher (P<0.001) CP and (P<0.001) NDF during period 2 compared to GWC. The difference in CP content remained higher (P<0.001) in AG. The in vitro organic matter digestibility (IVOMD) for AG sward was higher (P < 0.001) during period 2 but lower (P<0.03) during period 3. There were no differences in milk yield or milk composition between sward groups except for higher (P= 0.01) milk urea content from cows on AG swards. No difference in renneting capacity of the milk was found between swards. Keywords: white clover, herbage mass, herbage height, milk yield and composition. INTRODUCTION White clover (Trifolium repens L.) is considered as the most important temperate zone legume species that can persist under both frequent cutting and intensive grazing. It is best suited for maritime climate with mild winters and abundant rainfall during the growing season. The ability to fix atmospheric N, high nutritive value and significant impact on animal performance, emphasise white clovers importance in low input grazing systems. However, white clover has not played an important role in Scandinavian agriculture. This is mainly due to over-wintering risks, poor tolerance to low precipitation and the inability to compete with N-fertilised grasses in intensive production systems. As organic farming has gained acceptance by many farmers, white clover performance has also been studied under Scandinavian conditions, with short growing seasons, long snow cover period and rapid spring development. Such studies include white clover in mixtures for silage (Nykänen-Kurki 1994) and over-wintering and frost hardiness (Svenning et al. 1993). However, most of these trials were carried out as 'cutting only' experiments, with few grazing trials (Sormunen-Christian & Nykänen- Kurki 1995). Grazing processes such as trampling, selective grazing and deposition of dung and urine are known to influence both dry matter production and botanical composition of the sward (Laidlaw and Vertes 1993). There is a need for information on white clover production potential under grazing and animal performance in Nordic climates. This paper reports a study on herbage mass production and animal performance conducted on a low N-fertilised grass white clover based sward in comparison to a conventional N-fertilised all grass sward. MATERIALS AND METHODS Swards The experiment was conducted at the University of Helsinki Research Farm, Viikki. The grass-white clover (GWC) sward was established with 5 kg white clover, cultivar Lena, 8 kg timothy grass (Phleum pratense L.), and 15 kg meadow fescue (Festuca pratensis Huds.) per ha. The all-grass (AG) sward was established on the adjacent paddock with 5 kg red clover, 8 kg timothy grass and 15 kg meadow fescue per ha. Red clover had disappeared by the beginning of the experiment. The soil was