Productivity, water use and nitrogen fixation of annual-legume green-manure crops in the Dark Brown soil zone of Saskatchewan

Abstract

Both large-seeded annual legumes (pulse crops) and small-seeded annual or perennial legumes (forage crops) fix nitrogen (N) and can improve soil organic matter and fertility when used for green manuring. The role of pulses as green-manure crops has not been adequately evaluated in the Prairies, as they have been grown primarily as cash seed crops. An experiment was conducted in the Dark Brown soil zone at Saskatoon over four growing seasons on a moderately heavy-textured soil to determine the productivity, nitrogen fixation and soil moisture use of pea (Pisum sativum L. ’Trapper’), faba bean (Vicia faba L. ’Outlook’), lentil (Lens culinaris Medik. ’Eston’ and ’Indianhead’), Tangier flatpea (Lathyrus tingitanus L. ’Tinga’) and seedling alfalfa (Medicago sativa L. ’Moapa’) as green-manure substitutes for summerfallow. Dry-matter production (above ground) by full bloom averaged 6390, 4140, 3590, 2930 and 1260 kg ha−1 for pea, lentil, faba bean, Tangier flatpea and seedling alfalfa, respectively. Nitrogen yields were 166, 108, 119, 81 and 36 kg ha−1 and N fixation rates were 40, 15, 40, 24 and 4 kg ha−1 for pea, lentil, faba bean, Tangier flatpea and seedling alfalfa, respectively. Green-manure used similar amounts of water as wheat grown to maturity. Snow trapping by desiccating the standing green-manure crop was ineffective in increasing soil water in the spring. Low seeding rate and thus low cost of production made lentil the most reasonable choice as an annual-legume green-manure crop. However, improved methods of water conservation must be found to replace the water used to grow the green-manure crop. Key words: Pea, lentil, faba bean, Tangier flatpea, green manure, soil moisture