Influence of Nod factors on the quantity and distribution in faba bean of symbiotically fixed nitrogen as determined by the 15N isotope dilution method

Abstract

The influence of Nod factors (NFs) on faba bean (Vicia faba L.) in 2014–2016 was investigated in a field experiment located on soil classified as a Haplic Luvisol. Nod factors were isolated from the Rhizobium leguminosarum bv. viciae strain GR09. Faba bean was tested with NFs and without NFs, and the plants were harvested in two stages of growth: at the flowering and at full maturity. Plant parts were analyzed for biomass yield, N yield, and the amount of symbiotically fixed N. Based on the isotope dilution method (using N fertilizer in the form of ammonium sulfate [(15NH4)2SO4)], yields of N derived from the atmosphere, soil, and fertilizer were calculated. Nod factors did not have a significant influence on most of the investigated parameters, which were strongly differentiated by the amount of rainfall. However, NF application led to a significant increase in thousand-seed weight (by 5.4%) and, importantly, NFs beneficially affected N yield in seeds (an increase of 16% compared with the control), the whole mature plant (by 17%), as well as in stripped pods (by 24%) in the dry year 2015. The results showed some possibility of using NFs as a biofertilizer for increasing faba bean productivity, especially under unfavorable conditions during seasons with water deficiency in the soil.