A PRELIMINARY STUDY OF AGRICULTURAL SOILS INTENDED FOR CARBON SEQUESTRATION

As atmospheric carbon dioxide levels continue to rise due to input from fossil fuel burning and other human activities, the need for mitigation strategies becomes more urgent. One promising strategy is through carbon sequestration, the removal of carbon from the atmosphere and storage in various reservoirs. Agricultural soils that have been depleted of organic and inorganic carbon through years of unsustainable farming practices are one potential reservoir for long-term carbon storage. Carbon sequestration in agricultural soils is accomplished through best management practices such as no-till farming with crop residue mulch and increased application of manure and other biosolids.

In this research, preliminary studies were conducted on soils at a farm in Thorp, Washington which is being converted in order to sequester carbon. The farm, Spoon Full Farm, occupies approximately 80 hectares in a low terrace in the floodplain of the Yakima River. The farm has been producing hay for the past several decades using high inputs of fertilizer, pesticide, and irrigation water. In Spring 2017, they began a transition to a more diverse, organic farm that will produce vegetables, livestock, and tree crops using recommended management practices.

In this initial survey of Spoon Full Farm, measurements have been made of soil properties including soil texture, density, total organic matter, total carbon, carbonate content. LIDAR and digital surface maps show evidence on the farm terrace for side channels that were probably active regularly during high flows before the early 1900s, when flows became regulated on the Yakima River. Soils across the terrace are sandy loams to loamy sands with grain size distributions that are controlled by the locations of the soils in relation to the most recent side channels. Organic matter and organic carbon in farm soils is relatively low. For soils below 10 cm depth, total organic matter measured through loss on ignition ranges from 2.3% to 8.0% by weight and total organic carbon ranges from 0.6% to 1.9% by weight. Carbonate contents are typically around 0.15% by weight in farmed soils and slightly higher (0.2% to 0.8% by weight) in nearby unfarmed soils. The low carbon content of these soils, their sandy texture, and their good drainage provide high potential for carbon sequestration.