Nodulation and early growth of faba bean (Vicia faba L.) and pea (Pisum sativum L.) as affected by strain of Rhizobium, NO₃- supply, and growth temperature

Abstract

The effectiveness of each of two strains of Rhizobium, TA 101 and SU 39 1, on 'Fiord' faba bean and on two cultivars of pea 'A102' and 'Early Dun', was estimated in pot experiments. Plants were grown either without NO3- or with up to 7.5 mM NO3- and at 10, 15, and 20¦C to assess the effects of mineral nitrogen and of temperature on plant growth, nodulation, and nitrogen fixation (acetylene reduction).The strains TA 101 and SU 391 were slow to nodulate 'Fiord' faba bean (up to 50 days from sowing) but were rapid (20 days) on pea. TA 101 nodulated the pea cultivar 'A 102' significantly better than it did 'Early Dun', and was generally more effective in supplying N to its host than was SU 391 in the absence of NO3-.Nodule development in 'Fiord' inoculated with SU391 was slightly stimulated in the presence of 2.5 mM NO3-, which compensated for the poor early seedling growth which occurred when plants were grown without mineral nitrogen. Both 5.0 and 7.5 mM NO3- delayed nodulation, decreased nodule number and decreased nodule activity of 'Fiord'. NO3- also had a strongly depressive effect on nodulation and nodule activity of pea but strongly promoted plant growth.Seedling growth and nodulation were poorer at 10¦C than at either 15 or 20¦C in both faba bean and pea. Nodulation of 'Fiord' was markedly reduced by the low temperature, and it appears likely to be slow in the field when the soil temperature is low (10¦C) as may occur after late sowing. The known yield advantage of early planting of this cultivar may in part be due to better nodulation under warm (15¦C) soil conditions. It is concluded that strains TA 101 and SU 391 are not very effective on 'Fiord' faba bean, although poor seedling growth due to poor nodulation with these inoculants may be compensated for by soil mineral nitrogen. Concentrations of soil NO3- equivalent to 2.5 to 5.0 mM, however, may depress the capacity of both faba bean and pea to fix nitrogen in the field.