Type of pulse crop included in a 2-year rotation with wheat affects total N2O loss and intensity

A field study was conducted near Saskatoon, Canada, where area- and yield-scaled N2O emissions were evaluated for two rotation cycles of four pulse crops (chickpea [Cicer arietinum L.], faba bean [Vicia faba L.], lentil [Lens culinaris L.], and field pea [Pisum sativum L.]) followed by spring wheat (Triticum aestivum L.). A wheat-wheat sequence was included as a reference. Nitrous oxide emission measurements were made using non-steady-state chambers, and the respective contributions of growing season and spring thaw periods to cumulative emissions quantified. Of the pulse crops, lentil consistently produced the greatest cumulative N2O emissions—during both the pulse year and the subsequent wheat year—while pea consistently yielded the lowest cumulative N2O emissions. Area-scaled cumulative N2O emissions for the 2-year rotation cycles ranged from 1.64 kg N2O-N ha−1 for pea to 2.84 kg N2O-N ha−1 for lentil, and emissions for the 4-year study period ranged from 3.29 kg N2O-N ha−1 for pea to 5.69 kg N2O-N ha−1 for lentil. Ranking of pulse crop area-scaled emissions for the 4-year study was pea ≤ faba bean ≤ wheat = chickpea ≤ lentil. However, when emissions were scaled for yield, the rankings changed (pea = faba bean ≤ wheat ≤ lentil ≤ chickpea) with chickpea producing higher emissions than lentil per kg seed. Including pea and faba bean in rotation with wheat could mitigate N2O emissions whereas including chickpea and lentil in rotation with wheat failed to provide a beneficial effect in terms of mitigating N2O emissions and, on a yield-scaled basis, can even increase emissions compared to continuous wheat.