Nitrogen Balance for Pulse Crops in Rotation with Spring Wheat

Pulse crops, having the capacity for biological nitrogen (N) fixation, rarely receive N fertilizers, but information is scarce on N balance for pulse crops or pulse crop-spring wheat (Triticum aestivum L.) rotations. The objective of the study was to evaluate N balance based on N inputs and outputs and soil N sequestration rate for pulse crops and pulse crop-spring wheat rotations from 2021 to 2024 in the US northern Great Plains. Pulse crops (chickpea [Cicer arietinum L.], lentil [Lens culinaris Medik.], and pea [Pisum sativum L.]) were rotated with spring wheat to form four crop rotations (chickpea–spring wheat, lentil-spring wheat, pea–spring wheat, and spring wheat–spring wheat). Total N input from N fertilization, biological N fixation, soil N mineralization, crop seed, and precipitation was 9–27% greater for pea than for other crops and greater for pea–spring wheat than chickpea–spring wheat and continuous spring wheat. Total N output from grain N removal, ammonia volatilization, denitrification, plant senescence, leaching, surface runoff, and gaseous emissions was 20–62% greater for spring wheat than pulse crops. Nitrogen sequestration rate at 0–15 cm was 89% greater for spring wheat than lentil and 106–107% greater for pea-spring wheat and spring wheat–spring wheat than lentil–spring wheat. Nitrogen balance was 215–356% greater for chickpea and pea than lentil and spring wheat and 114–118% greater for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat. Greater N input increased N surplus for pea or pea-spring wheat, and greater N output increased N deficit for spring wheat or spring-spring wheat compared to lentil or lentil–spring wheat, indicating that pea alone or in rotation with spring wheat reduced N loss to the environment by increasing soil N storage compared to continuous spring wheat.