Soil carbon loss from newly drained Red River Basin Soils

Anna Cates

There is an inherent tension between subsurface drainage and soil organic carbon (SOC). Drainage-induced aeration increases SOC mineralization and reduces SOC stocks (Fernandez 2016). Lower SOC is related to poor soil structure, low fertility and poor crop yields, but in the context of poorly-drained soils, increased soil aeration is likely to have a net positive yield effect. Reducing SOC stocks may be tolerable if aeration-induced gains in crop productivity and high rates of residue buoy SOC at a moderate level and maintain soil health in the long term. Drainage has been shown to increase nitrogen use efficiency (NUE) and reduce N20 emissions, so overall greenhouse gas emissions from drained systems may be lower despite mineralization of SOC (Castellano et al. 2019). Farmers continue to pursue drainage because more reliably productive lands offer economic stability to individuals and communities. In the Red River Basin of the North, drainage is rapidly expanding alongside the range of com and soybeans, so it is an important time and place to investigate the balance between profitability, environmental stewardship, and productivity with drainage.

We propose to quantify SOC losses in newly drained fields at the University of Minnesota NW Research and Outreach Center (NWROC). Initial samples were taken prior to drainage installation in fall 2019, and drained and undrained fields will be sampled at the same points three times during the 2020 growing season. Samples will be analyzed for total SOC as well as active C fractions, in order to determine which pools of SOC are lost as drained systems equilibrate. Understanding which pools are most rapidly and drastically depleted after drainage will guide future research questions. Specifically, we hope to investigate soil greenhouse gas emissions, NUE of com and wheat, field workability, and varying tillage and residue management protocols within the drained and undrained plots in future seasons. Our long-term goal is to support growers with research-based recommendations for productive, environmentally responsible agroecoystem management. Management recommendations for drained conditions are overdue in the Red River Basin of the North, and minimal research exists on this topic.