Variation in soil organic carbon over time in no-till versus minimum tillage dryland wheat-fallow

Authors: Wuest, Stewart; SCHILLINGER, WILLIAM - Washington State University; MACHADO, STEPHEN - Oregon State University

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2023
Publication Date: 2/17/2023
Citation: Wuest, S.B., Schillinger, W.F., Machado, S. 2023. Variation in soil organic carbon over time in no-till versus minimum tillage dryland wheat-fallow. Soil & Tillage Research. 229. Article 105677. https://doi.org/10.1016/j.still.2023.105677.
DOI: https://doi.org/10.1016/j.still.2023.105677

Interpretive Summary: Interest in soil organic carbon (SOC) levels is focused on both soil quality and sequestering carbon from the atmosphere. Farmers have developed minimal tillage systems and no-till systems. This study carefully measured SOC at three sites where long-term, randomized, replicated studies included a comparison of minimum tillage and no-till rotations in the low precipitation inland Pacific Northwest, USA. To overcome seasonal, annual, and rotational effects, a soil sample was taken from each plot monthly for three years. Averages of monthly samples revealed the tilled treatment had an SOC of 7.21 g kg-1 compared to 7.04 for the no-till treatment (p < 0.004). Examining variation month-to-month, 93% of sample variation was due to the sample date, and 7 percent due to blocks (replications) within sites. Power calculations estimate 34 to 100 samples would be required to detect a difference of 5% given the data’s standard deviation. Soil water and soil temperature to 30 cm was measured at the time of sampling, and while no-till more often had greater water, temperature differences were inconsistent. We conclude that no-till did not result in more soil carbon in these systems and judicious tillage is an option for sustainable production.

Technical Abstract: Interest in soil organic carbon (SOC) levels is focused on both soil quality and sequestering carbon from the atmosphere. Farmers have developed minimal tillage systems and no-till systems. This study carefully measured SOC at three sites where long-term, randomized, replicated studies included a comparison of minimum tillage and no-till rotations in the low precipitation inland Pacific Northwest, USA. To overcome seasonal, annual, and rotational effects, a soil sample was taken from each plot monthly for three years. The top 250 kg m-2 dry soil mass (representing the 0- to 20-cm depth) from each core was analyzed for SOC. Averages of monthly samples revealed the tilled treatment had an SOC of 7.21 g kg-1 compared to 7.04 for the no-till treatment (p < 0.004). Examining variation month-to-month, 93% of sample variation was due to the sample date, and 7 percent due to blocks (replications) within sites. Of 77 individual site by date samples, only 6 produced significant t-tests (p < 0.05) but SOC differences were 46 to 31 in favor of tillage and those 46 had larger differences. Power calculations estimate 34 to 100 samples would be required to detect a difference of 5% given the data’s standard deviation. Soil water and soil temperature to 30 cm was measured at the time of sampling, and while no-till more often had greater water, temperature differences were inconsistent. We conclude that no-till did not result in more soil carbon in these systems and judicious tillage is an option for sustainable production.