Effect of Two Seeding Rates on Nitrogen Yield and Nitrogen Fixation of Winter and Spring Faba Bean.

Faba bean ( Vicia faba L. minor ) is an important grain legume and is widely used as food and feed. It is traditionally used as a spring crop in Central European cropping systems. There is increasing interest in winter faba bean due to a higher yield potential, but limited knowledge of nitrogen (N) yields and nitrogen fixation (N FIX ) exists. Therefore, the purpose of this study was to compare N concentrations, N yield of plant fractions, soil mineral N (SMN) and SMN sparing in the soil after harvest, N FIX and N balance of two winter faba bean varieties (Diva and Hiverna) to those of a spring faba bean (Alexia) using two seeding rates (25 versus 50 germinable seeds m -2 ) in a two-year field experiment under Pannonian climate conditions in eastern Austria. The winter faba bean varieties had higher N yields and N FIX , not only due to higher biomass yields, but also due to higher N concentrations and a higher percentage of N derived from atmosphere in the biomass. Conversely, the soil mineral N after harvest was lower compared to the spring faba bean. All treatments had a negative N balance due to higher grain N yield than N FIX . Winter faba beans left higher amounts of biologically-fixed N in residues for the subsequent crop, whereas spring faba bean left more SMN. Winter faba bean varieties obtained good results with both seeding rates, whereas the grain yield and the grain N yield of Alexia tended to higher with the higher seeding rate.