Seasonal dynamics of the weed population in established alfalfa (Medicago sativa L.) in Pelagonia region, Republic of Macedonia.

Survey of seasonal dynamics of the weed population in established alfalfa was conducted during 2006-2008 in Pelagonia region Republic of Macedonia. The objective of this study was to identify weeds of importance and to determine qualitative and quantitative structure of weed population in individual cuts and years of growing in established alfalfa. The weed population consisted mainly of perennial and annual winter grasses and some broadleaf weeds. Weed species and weed density decreases from the first to the fourth cut, but increases with the years of alfalfa growing, from second to the fourth year. During the floristic research in all years of alfalfa growing, 36 weed species were registered and determined. Anthemis cotula (average of 11.5 plants m -2 ), Digitaria sanguinalis (14.3) and Millium vernale (27.5) were the most dominant weeds in the second, third and fourth year of alfalfa growing, respectively. From the taxonomic aspect, the weed flora was distributed in 11 families. Twenty five weed species were dicotyledons and 11 weeds were monocotyledons. The most abundant species were from the families Poaceae and Asteraceae (11 weed species). Therophytes were dominant life form category (24 weed species), although their number significantly decreased from first to fourth cut every year. The number of hemicryptophytes increased with the years of alfalfa growing, from second to the fourth year. Only the presence of geophytes was more or less constant, regardless of cuts and year of alfalfa growing. Detected weed population indicated habitat with favorable thermal and light regimes, slightly acid to neutral soil pH, moderately moist and medium to high supply of nitrogen and nitrogen-containing compounds.