HERBAGE YIELD AND NITROGEN ACCUMULATION BY 7 LEGUME CROPS ON ACID ANDNEUTRAL SOILS IN A SUB-ARCTIC ENVIRONMENT

Alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), yell ow sweetclover (Medicago officinalis L.), fababean (Vicia faba L.), le ntil (Lens culinaris Medik.), pea (Pisum sativum L.), and white lupin (Lupinus albus L.) were evaluated as annual crops in central Alaska on neutral and acid soils for their potential herbage productivity and N accumulation. Herbage dry matter yields were high on the neutral soil , with an overall average yield of 6927 kg ha-1. Yields were much lowe r at the cooler, acid soil site with an overall average yield of 3743 kg ha-1 for inoculated legumes. Herbage N concentrations ranged from 1 4 to 36 mg g-1. Amounts of N-fixation, as estimated by the total N dif ference method, ranged from <50 kg ha-1 for some legumes on the acid s oil to >200 kg ha-1 for fababean on the neutral soil. Inoculation resu lted in increases in nodulation, growth and apparent N-fixation on the acid soil where legumes had not previously been grown, but were usual ly not significant on the neutral soil where legumes had been grown fo r many years. Liming the acid soil resulted in significant increases i n soil pH and in nodulation, herbage yield, and herbage N yield.