Soil carbon stocks response to subsurface drainage in the North Willamette Valley

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: 3/1/2024
Publication Date: 4/25/2024
Citation: Breza, L.C., Moore, J.M., Tomasek, A., Trippe, K.M. 2024. Soil carbon stocks response to subsurface drainage in the North Willamette Valley. Seed Production Research at Oregon State University. 11-14.

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 of Oregon 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 survey in the northern Willamette Valley on artificially and naturally drained grass seed production fields. We collected soil cores from grass seed fields located on moderately well drained soils to a depth of 1 m and partitioned them into different sections based on depth. We measured total C and nitrogen (N) for each depth, within each field. We found that cumulative soil C did not differ between the different drainage treatments and soil C was related to soil texture. Though it is not statistically significant, there is a trend of slightly higher C stocks in old and untiled fields compared to newly tiled fields. This trend could indicate an initial loss of soil C after subsurface drainage installation in new tile fields, but a recovery of soil C in old tile fields as the system stabilizes over time. These results reiterate findings from previous studies in the South Willamette Valley conducted on poorly drained soils, however, increased replication of field treatments is needed to verify this trend.

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, Oregon 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 survey in the northern Willamette Valley that identified an age gradient of tile drainage systems within grass seed cropping systems. We collected soil cores from grass seed fields located on moderately well drained soils, which included Woodburn (Fine-silty, mixed, superactive, mesic Aquultic Argixerolls), Carlton (Fine-silty, mixed, superactive, mesic Aquultic Haploxerolls), and Coburg (Fine, mixed, superactive, mesic Oxyaquic Argixerolls) soil series. Soils were collected to a depth of 1 m and sectioned based on depth. We measured total C and nitrogen (N) for each section, within each field. We found that cumulative soil C did not differ between the different drainage treatments and soil C was related to soil texture. Though it is not statistically significant, there is a trend of slightly higher C stocks in old and untiled fields compared to newly tiled fields. This trend could indicate an initial loss of soil C after subsurface drainage installation in new tile fields, but a recovery of soil C in old tile fields as the system stabilizes over time. These results reiterate findings from previous studies in the South Willamette Valley conducted on poorly drained soils, however, increased replication of field treatments is needed to verify this trend.