THE USE OF ANNUAL LEGUME GREEN-MANURE CROPS AS A SUBSTITUTE FOR SUMMERFALLOW IN THE PEACE RIVER REGION

Field studies were conducted on a Landry clay-loam soil (Black Solod) to evaluate the effects of green manuring Tangier flatpea (Lathyrus ti ngitanus 'Tinga'), lentil (Lens culinaris 'Indianhead') and alfalfa (M edicago sativa 'Moapa') on subsequent barley (Hordeum vulgare 'Galt') crops. Each trial consisted of separate legume phases planted in 1984, 1985 and 1986 and barley phases in each of the subsequent years. The flatpea and lentil were incorporated (green manured) in late July or i n late August to early September. The alfalfa was incorporated in late August to early September. The 3-yr mean dry matter (DM) yields of le ntil and Tangier flatpea varied from 1047 to 2308 kg ha-1, with consid erable variability from year to year. Alfalfa, used as an annual legum e, produced 812 kg DM ha 1. Dinitrogen fixation by the annual legumes, as assayed by acetylene reduction was 16 kg N ha-1 or less. Soil mois ture measurements following the legumes showed 2-3 cm less water in th e profile to a depth of 120 cm following alfalfa and late-incorporated Tangier flatpea than following summerfallow and early-incorporated le ntil and Tangier flatpea. Ammonium-N levels in the soil were similar f ollowing the various legume green-manure treatments. Nitrate-N levels following the legumes were variable, but the levels of nitrate-N in th e plots following legume incorporation generally followed the order: f allow > early incorporation > late incorporation. The grain and N yiel d of barley following early-incorporated lentil and flatpea were equal to or only slightly less than the yield following fallow, suggesting that annual legumes have a good potential as green-manure crops in pla ce of fallow in Black Solod soils of the Peace River region.