Assessment tool for biological nitrogen fixation of Vicia faba cultivated as spring main crop

Published data on experiments with faba bean were used to develop a software tool for estimating the amount of nitrogen fixed (separately in grains and harvest residues) and the percentage of total nitrogen derived from the atmosphere (%Ndfa) from a minimum input data set of soil parameters (soil texture or, if available, soil yield potential, mineral nitrogen at the time of seeding, soil pH) and water supply during the period of growth. The tool is applicable for cropping situations in Central and Western Europe, where faba bean is grown as a spring crop. It is designed either for an assessment after the harvest of the crop (grain yield known) or for anticipating the nitrogen amounts resulting from cropping situations in the future (grain yield unknown). For the latter case a rough yield estimate is included. A comparison of estimated values of fixed nitrogen (t ha−1) and percentage of nitrogen derived from the atmosphere (%Ndfa) with data from the literature yielded coefficients of determination (r2) of 0.53 for the amount of fixed nitrogen and 0.29-0.63, depending on the used dataset, for %Ndfa.