Plasticity of Indeterminate Field Bean in Response to Seed Density and Fertilizer Supply.

Field bean (Vicia faba minor Beck), probably originated in the pre-historic period in the Middle East is, today, cultivated all over the world and counts among the most widely adapted grain legumes. In the Mediterranean region, field bean is considered a viable alternative to soybean to increase the sustainability of farming systems, because of its rusticity, and low fertilizer and pesticides requirement. Due to the indeterminate growth habit, intra-plant competition between reproductive and vegetative structures and among the developing pods may be great. Warmer winter temperatures, such those expected in the consequence of climate change, favour intra-plant competition, as they promote vegetative growth and flowering parallel to seed filling. A 3-year field experiment was carried out in temperate Mediterranean conditions on loam soil with moderately alkaline reaction. Imposed treatments were NP fertilizer supply (0, and 120 kg N ha-1 and 100 kg P ha-1) and seed density (100 and 60 seed m-2, respectively indicated as Fb100 and Fb60). Heavy rainfall in autumn-winter delayed sowing date, which was performed on October 26th 2017, December 11th 2018, and February 12th 2020. Plants were harvested twice each year, at the stage of full flowering with basal pods developing (65-73, BBCH) and when plants were dead and dry (97, BBCH). Seed yield was not affected by seed density, in that field bean sown at lower density adjusted for the lower number of stems per unit surface increasing by 25% the number of pods per stem, which was obtained by increasing the number of fertile pods per raceme rather than the percentage of fertile nodes per stem. The supply of NP fertilizers increased seed yield by 18%, because of a higher number of seeds per pod. February sowing markedly reduced seed yield because of lower number of seeds per pod and mean seed weight.