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Intercropping wheat and barley with nitrogen fixing legume species in low input organic systems Chapagain, Tejendra


Declining land productivity associated with decreasing soil organic carbon (SOC) and nitrogen (N) is an issue for conventional production of small grains. Intercropping grains with legumes may provide a sustainable solution. I grew wheat (Triticum aestivum cv. ‘Scarlet’) as a monoculture and intercropped with either common bean (Phaseolus vulgaris cv. ‘Red Kidney’, or cv. ‘Black Turtle’), or fava bean (Vicia faba cv. ‘Bell’) in rows of wheat:bean 1:1 and 2:1 as well as broadcast arrangements to assess the effects of genotype and spatial arrangements on crop agronomy, land productivity, biological nitrogen fixation and transfer, N and carbon (C) accumulation in aboveground biomass, soil N balance, gross ecosystem photosynthesis (GEP), net ecosystem productivity (NEP), and water use efficiency (WUE). Barley (Hordeum vulgare cv. ‘Oxbridge’) and pea (Pisum sativum cv. ‘Reward’) were also included based on synchronized maturity, yield potential, protein content, and root architecture. Stable isotope methods (¹³C and ¹⁵N) coupled with field CO₂ exchange measurements were used to determine C and N transformations. Intercrop plots had higher land productivity, improved grain and biomass quality, increased legume nodulation and percent N derived from symbiotic N₂ fixation. Wheat-fava bean in the 1:1 arrangement displayed a 50% increase in land productivity. Barley-pea in the 2:1 arrangement also had the highest total land outputs (5.9 t ha-¹) and land equivalent ratio (1.32). Wheat-fava bean in the 1:1 arrangement fixed the highest amount of N (74 kg N ha-¹), transferred the most N (13% of N in wheat), and accumulated more C (26% higher than wheat monoculture) in shoot biomass. WUE of wheat was improved when grown with fava bean. Pea in intercrop plots also displayed increased nodulation (27-45%) and symbiotic N₂ fixation (9-17%) leading to the addition of 60-78 kg N ha-¹. The GEP and NEP were highest in the 2:1 arrangement and led to the highest daytime C sequestration (229 mg C m-² hr-¹). I demonstrated that intercropping small grains with legumes, in specific spatial arrangements and under low input organic conditions, can counter conventional monoculture-associated SOC and N losses through higher land and ecosystem productivity, and greater organic N-fixation and transfer.

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Attribution-NonCommercial-NoDerivs 2.5 Canada