Institute of Forage crops, 5800–Pleven, Gen. V. Vazov street, 89, BULGARIA,
Abstract. Eight Bulgarian alfalfa varieties (Prista 2, Prista 3, Prista 4, Obnova 10, Pleven 6, Dara, Multifoliate and Dama) and one French variety (Europe) were cultivated on slightly leached chernozem in Institute of Forage Crops (Pleven) during the period 2006–2009. The dynamics in alfalfa nodulation by years showed the greatest number of nodules on average per plant was formed during the second year of development (8.1) followed by third (6.5) and first year (6.3). Least nodules were formed in the fourth year (1.2) as the decrease to the previous three years was sensitive (by 82.9%). In all years (except first year) the intensity of nodulation decreased from spring regrowth to summer and autumn regrowth. The main quantity of nodules was situated on the lateral roots as in the first year their percentage was 52.4 and during the second, third and fourth year–86.4, 95.4 and 100% respectively. With most pronounced nodule–forming ability for the Bulgarian varieties were Obnova 10 and Multifoliate and the French variety Europe.The alfalfa nodulation correlated with important parameters: age of stand (r= –0.729), stand density (r= –0.648), number of stems per plant (r= 0.763) and weight of root mass (r= 0.384).
Keyword: alfalfa, correlations, nodulation, varieties