A meta-analysis approach to examining the greenhouse gas implications of including dry peas (Pisum sativum L.) and lentils (Lens culinaris M.) in crop rotations in western Canada

This study used a meta-analytic approach to systematically examine changes in greenhouse gas (GHG) emissions intensities (i.e., carbon footprints) between pulse-containing and pulse-free crop rotations in western Canada. A systematic literature review was conducted to identify published literature relevant to the goal of the analysis and meta-analysis was conducted to determine statistically significant differences in GHG emissions between pulse-free and pulse-containing crop rotations. Four pulse-free reference rotations (cereal-cereal [CC]; oilseed-cereal [OC]; oilseed-oilseed [OO]; and cereal-oilseed [CO]) were compared to rotations where the first crop in each two-year sequence was replaced with either dry pea (Pisum sativum L.) or lentil (Lens culinaris M.). Two scenarios were considered. The first scenario investigated the effects of dry peas and lentils when synthetic nitrogen (N) applied to cereal and oilseed crops grown after pulses was not reduced (i.e., no change) (NN). The second scenario (NCR) investigated the effect of dry peas and lentils when synthetic N application rates were reduced to the maximum extent possible (i.e., credit) to maintain subsequent crop yields. Pooled analyses demonstrated that, in general, cereal and oilseed crops grown after a dry pea or lentil crop had similar or reduced GHG emissions compared to those grown after a cereal or oilseed. The GHG emissions from cereal and oilseed crops grown after dry peas and lentils were higher in NN (888-987 kg CO2e/ha; 286-598 kg CO2e/t) than in NCR (311-978 kg CO2e/ha; 116-598 kg CO2e/t), suggesting that emissions were reduced to a greater extent when pulse crops offset the N fertilizer requirements of a subsequent crop compared to when they were used to provide N to maximize crop yields. In two-year rotations, the inclusion of pulses reduced GHG emissions compared to all reference rotations in both NN (savings of 475-719 kg CO2e/ha over two years [area basis]; 164-496 kg CO2e/t over two years [yield basis]) and NCR (savings of 489-1185 kg CO2e/ha over two years [area basis]; 335-610 kg CO2e/t over two years [yield basis]), mostly as a result of reduced synthetic N requirements of the whole rotation. The results of the analysis are presented by crop for each pulse-free and pulse-containing cropping sequence for each scenario to allow for flexibility in comparing GHG emissions from various rotations.