Mind Your Peas: Carbon and Nitrogen in a Pulse Crop Rotation.

Cropping systems in the Canadian Prairies have become specialized based on the most readily marketable and profitable crops, which has led to an intensification of crop rotations with a few crops. These traditional cropping systems have relied on the input of non-renewable energy, particularly nitrogen fertilizer. Pulse crops may provide an option for improving the sustainability of these systems. The ability of pulse crops to fix atmospheric N has been well documented. However, the amount of N available in the following growing season and its conversion into mineral N forms needs to be measured to better understand the N benefits of including pulse crops in a rotation. Also, it is suspected that pulse crops have additional benefits to soil quality, specifically in terms of soil organic carbon. Soil carbon additions from crop residues impose a control on mineralization rates and can dictate N available to succeeding crops. However it is difficult to isolate crop residue influences on soil organic matter, particularly below ground residue additions. This project measures various forms of nitrogen throughout the growing season using stable isotopes as influenced by pea in comparison to canola in rotation. As well, an investigation regarding the suitability of repeat pulse 13C atmospheric labeling of plant material for determining the effect of crop residue additions to soil organic carbon will be discussed.