The research was conducted in 1999-2001 on degraded chernozem at the Experimental Station at Prusy near Krakow to determine yielding and yield structure components of two field bean cultivars with different growth rhythm under conditions of diversified sowing rate, row spacing and crops undersown in the field bean canopy. Seed yield of investigated field bean cultivars (Optimal and Sonet) ranged between 3.93 and 5.78 t/ha. Supplementary crops phacelia and fodder radish did not influence significantly the seed yield. Sonet cultivar yielded 22% better in comparison with Optimal. Similar tendencies were registered for total protein yield. Larger yield produced by Sonet cv. was caused by a significantly higher number of pods and seeds per plant. Traditional cultivar was characterized by a higher LAI value during the period of pod formation, i.e. at the time of greatest demand for assimilates by generative organs.