EFFECT OF LOW LEVEL NITROGEN FERTILIZATION ON NODULATION, ACETYLENE REDUCTION AND DRY MATTER IN FABABEANS AND THREE OTHER LEGUMES

Abstract

Acetylene reduction in fababeans (Vicia faba L.) was significantly greater than in peas (Pisum sativum L.) and black beans (Phaseolus vulgaris L.) in 1977, and peas and soybeans (Glycine max L.) in 1978. More than 90% of fababean, pea and soybean plants bore nodules, but only 77% of black beans. The addition of 20 kg N/ha as ammonium nitrate depressed nodulation in all species in 1977, especially black beans. Acetylene reduction was also depressed in all species. Results in 1978 on a higher nitrate soil were more variable, though a marked decrease in acetylene reduction in peas due to fertilizer N was again recorded. Of the four species, only fababeans regrew after maturity; acetylene reduction was detected until 20 Oct. 1978. In spite of low fixation rates, black beans yielded significantly more dry matter and N than fababeans and peas. N fertilizer produced significant increases in dry matter in all species except fababeans. N yield was significantly increased by fertilizer in soybeans.