effect of planting date and genistein application on nitrogen content and nodulation in three annual medic speciees

to study the effect of planting dates and genistein application on nitrogen content and nodulation of three annual medic species (medicago polymorpha cv. santiago m. rigidula cv. ragidula, and m. radiata cv. radiata), an experiment was conducted during 2005-2006 in the research farm of faculty of agriculture, shahed university, tehran. the treatments were arranged as split split plot in a randomized complete block design with four replications. planting dates (february 20, march 1 and 11) were randomized to main plots while three annual medics allocated to sub-plots plus genistein (0 and 20 ?m) randomized to sub-sub-plot units. plant nitrogen content, nodulation and other traits were significantly affected by species. m. polymorpha was affected more than other species with respect to dry nodule weight, nodule number and number of nodules in cluster, nodule cluster number as well as nodule diameter. medicago rigidula exhibited a better resistance to cold than other varieties, with its forage yield and nitrogen percent higher than m. polymorpha. therefore, m. rigidula may be better adapted to cold zones. twenty ?mol of genistein remarkably affected nodulation and nitrogen percent of annual medics as compared to control. the results indicated that genistein modified the negative effect of low temperature on nodulation and nitrogen percent of annual medics. nodulation and nitrogen content (percent) increased in all varieties for the first planting date. this emphasizes that genistein had considerable effect on cold resistance establishment in varieties for improving nodulation and increasing plant nitrogen (percent) at farm growing conditions.