The use of annual legume green-manure crops as a substitute for summerfallow in the Peace River region

Abstract

Field studies were conducted on a Landry clay-loam soil (Black Solod) to evaluate the effects of green manuring Tangier flatpea (Lathyrus tingitanus 'Tinga'), lentil (Lens culinaris 'Indianhead') and alfalfa (Medicago 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 in late August to early September. The alfalfa was incorporated in late August to early September. The 3-yr mean dry matter (DM) yields of lentil and Tangier flatpea varied from 1047 to 2308 kg ha−1, with considerable variability from year to year. Alfalfa, used as an annual legume, 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 moisture measurements following the legumes showed 2–3 cm less water in the profile to a depth of 120 cm following alfalfa and late-incorporated Tangier flatpea than following summerfallow and early-incorporated lentil and Tangier flatpea. Ammonium-N levels in the soil were similar following the various legume green-manure treatments. Nitrate-N levels following the legumes were variable, but the levels of nitrate-N in the plots following legume incorporation generally followed the order: fallow > early incorporation > late incorporation. The grain and N yield 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 place of fallow in Black Solod soils of the Peace River region. Key words: Legume plow-down, soil conservation, dinitrogen fixation, soil moisture, nitrate-N