Field symbiotic fixation using 15N : II. Vicia faba L. and Pisum sativum L.

Abstract

A two-year experiment in two Orthic Luvisols in Portugal (ENMP and CV), with uninoculated and inoculated faba beans (Vicia faba) and peas, was set in randomized blocks, replicated five times. Barley was used as control crop. At sowing, 20 kg N/ha as 15(NH4)2SO4 4.8 atom% 15N excess were applied in each microplot. Plants were harvested at physiological maturity. In the lst year experiment, dry-matter, N yield and fixation in both crops were higher at CV soil, probably due to its higher fertility, namely the higher Mo content. In faba bean, % Ndfa varied from 65% at ENMP soil to 90% at CV, corresponding to N2-fixed of 80 and 125 kg N/ha; for peas, % Ndfa ranged from 35% to ENMP to >85% at CV, corresponding 22 and 107 kg N2-fixed/ha. Sites and years statistically affected crops, mainly by the deficient Mo level at ENMP, and drought stress in the 2nd year. Inoculation did not significantly affect fixation of faba bean, but significantly affected pea. Values of % Ndfa were >60%, for both crops, at both sites, but due to the hydric stress in the 2nd year, N2-fixed was lower than in the 1st year: an average of 70 kg N/ha by faba bean, and 37 to 55 kg N/ha, respectively by uninoculated and inoculated peas at CV. At ENMP, pea poorly fixed N2, and negative values for % Ndfa in the pea straw were found.