The dynamics of botanical composition of pure and mixed grass swards on peaty soil

Major part of forage grass varieties used for (re-)seeding Estonian grasslands is imported. Little is known about their performance is severe microclimatic conditions on peat soils as official testing takes place on mineral soils. A field trial comprising 7 pure-sown grass species (8 domestic, 11 foreign varieties) and 9 mixtures composed of local varieties was sown to drained peaty soil. The aim was to determine the sward components, which preserve there. Changes in grass sward composition were observed in 2005-2007. Among pure stands, Estonian Alopecurus pratensis variety ʹHaljasʹ, Phleum pratense ʹTiaʹ and ʹTikaʹ, Bromus inermis ʹLehisʹ maintained the highest percentages (86.0-92.8) of cultivated species by the third harvest year. Only B. inermis survived a harsh winter with negligible winterkill. The frost devastated the stands of Festulolium, Festuca pratense and F. arundinacea. ʹLehisʹ turned out to be the most winter and drought resistant also in mixed grass swards. If added at a rate of 30 kg ha-1 to the mixtures with P. pratense, B. inermis effectively outcompeted the herbs (range 1.4-8.2%) by the third harvest year and became dominant (72.3-87.1%). P. pratense ʹTiaʹ persisted for three years but gradually withdrew when was competing with B. inermis, and also with A. pratensis. Phalaris arundinacea was intolerant to three harvests per year at a cutting height of 7 cm and steadily declined from the swards. Dactylis glomerata and F. pratense were vulnerable to winterkill, but could partly recover at the end of a rainy season.