Comparison of Biological Nitrogen Fixation and Greenhouse Gas Emissions during Production of Pea, Lentil, Chickpea, and Fababean.

The inclusion of pulses in crop rotations benefits the sustainability of agro-ecosystems by replacing some fertilizer N with biologically fixed N.   Reducing fertilizer N additions can result in lower emissions of nitrous oxide (N₂O) both in the pulse crop phase of the rotation and in the subsequent phase. A field experiment was established in Saskatchewan, Canada to monitor greenhouse gas (GHG) emissions during the growing season of field pea, lentil, chickpea and fababean. Greenhouse gas emissions were measured using standard, non-steady state vented chambers. Biological nitrogen fixation (BNF) by the pulse crops was measured using the isotope dilution method.

The amount of N₂ fixed by whole plant ranged from 91 to 148 kg ha^-1, and increased in the order: pea < lentil < chickpea < fababean. The amount of fixed N in the crop residues varied with crop species, with 23%, 40%, 50% and 71% recovered in the fababean, pea, lentil and chickpea residues, respectively. Cumulative annual emissions of N₂O (1.3 to 1.9 kg N₂O-N ha^-1) and CO₂ (5192 to 6594 kg CO₂-C ha^-1) were greater in chickpea and lentil than fababean and pea. Soils were a net CH₄ sink with cumulative annual uptake ranging from -592 to -865 g CH₄-C ha^-1; differences among crops were not significant. Chickpea produced higher residue biomass than other crops. The residue biomass of the fababean, pea and lentil were comparable, but the amount of both N fixed by residues and N₂O emssions followed the order: fababean < pea < lentil, indicating that BNF was a direct source of N₂O emissions.