The effect of subsurface drainage in grass seed fields on soil carbon stocks

Authors: Breza, Lauren; Moore, Jennifer; TOMASEK, ABIGAIL - Oregon State University; Trippe, Kristin

Submitted to: Seed Production Research at Oregon State University
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2023
Publication Date: 7/1/2023
Citation: Breza, L.C., Moore, J.M., Tomasek, A., Trippe, K.M. 2023. The effect of subsurface drainage in grass seed fields on soil carbon stocks. Seed Production Research at Oregon State University. 2022:15-19.

Interpretive Summary: Subsurface drainage, known also as tile drainage, is a water management technique used to lower the water table in poorly drained soils. Growers in the Willamette Valley rely on tile drainage to reduce flooding, prevent erosion, and maintain field access during the months-long rainy season. Willamette Valley soils are high in soil carbon (C) and producing grass seed crops lends itself to many of the soil health principles that aim to sequester and keep C in the soil. However, there is virtually no research that explores the impact of tile drainage systems on soil health and the fate of soil C. Our research objective is to investigate how new tiled, old tiled, and untiled fields may increase or decrease soil C stocks. To accomplish our objectives, we conducted a field study in the southern Willamette Valley on artificially and naturally drained grass seed production fields. We collected soil cores (Dayton series) from grass seed fields to a depth of 1 m and partitioned them into different sections based on soil horizons falling above, within, and below the soil layer containing Malpass clay. We measured total C and nitrogen (N) for each horizon, within each field. We found that cumulative soil C did not differ between the different drainage treatments and that soil C decreased with depth. Additionally, there were no differences in soil C or N between the drainage treatments in the two upper horizons. However, there was more soil C and N in the old tile fields in the deepest horizon. These findings indicated that tile drainage may promote the accumulation of deep soil C in the long term. More research is needed to fully understand the mechanisms driving these patterns.

Technical Abstract: Subsurface tile drainage is a water management technique used to mitigate high water tables in poorly drained soils. Growers in the Willamette Valley rely on tile drainage to improve soil moisture conditions during the months-long rainy season. Willamette Valley soils are high in soil carbon (C) and producing grass seed crops lends itself to many of the soil health principles that aim to sequester and keep C in the soil. However, there is virtually no research that explores the impact of tile drainage systems on soil health and the fate of soil C. Our research objective is to investigate how new tiled, old tiled, and untiled fields may increase or decrease soil C stocks. To accomplish our objectives, we conducted a field study in the southern Willamette Valley that identified an age gradient of tile drainage systems within grass seed cropping systems. We collected soil cores (Dayton series) from grass seed fields to a depth of 1 m and sectioned cores based on horizons falling above (Ap/E), within (Bt), and below (BC) the argillic horizon. We measured total C and nitrogen (N) for each horizon, within each field. We found that cumulative soil C did not differ between the different drainage treatments and soil C decreased with depth. Additionally, there were no differences in soil C or N between the drainage treatments in the Ap/E and Bt horizons. However, there was more soil C and N in the old tile fields within the BC horizon (p < 0.001). These findings indicated that tile drainage may promote the accumulation of deep soil C in the long term. More research is needed to fully understand the mechanisms driving these patterns.