Contribution Of Cover Crop Roots To Soil Fertility And Crop Nutrition In Organic Spring Wheat In Quebec, Canada.

Assessing the contribution of cover crops (i.e. crops that are planted to improve soil health – not for harvest) to soil fertility is particularly complex. Little is known about how much N and how N from decomposing cover crop roots will become available to subsequent crops. The objective of the project was to determine the respective N contribution of shoots and roots of annual cover crop species to crop N uptake in organic spring wheat. A 2-year field experiment was conducted twice (2016-2017, 2017-2018) in Quebec, Canada. Cover crops were grown and terminated in Year 1, and a cash crop of spring wheat was grown the subsequent year (Year 2). Four annual cover crop species (common vetch, field pea, forage radish, and cereal rye) and four cover crop biomass input levels (shoot only, root only, and shoot plus root) were tested. Forage radishes and peas produced the highest total biomass (shoot and root) while radishes produced the highest root biomass. Common vetch had higher shoot N concentration than other species whereas its root N concentration was similar to radishes and peas. At spring wheat seeding, soil mineral N content (0-45 cm) was significantly higher in whole CC treatments (39 kg N ha-1) compared to treatments of shoot or root only (33 and 29 kg N ha-1, respectively). In 2017, spring wheat yields were higher following the whole CC than following the shoot or root parts only. Improving our understanding on soil N budget may help to reduce N losses from cover crop-based cropping systems such as organic farming systems. On a broader scale, this research aims to reduce the impact of organic farming on the environment by increasing its N use efficiency.