Soil Carbon Stocks and Radiocarbon Profiles in Three Agricultural Systems of California’s Central Valley

Anh Trinh , Kari M Finstad, Karis Jensen McFarlane , Rodolfo Huerta, Megan Kan, Jennifer Pett-Ridge, Aidee Guzman

Carbon stocks alone do not describe the age composition of soil carbon. We examined how soil carbon stocks and bulk radiocarbon varied with depth among fields with contrasting management histories in California's Central Valley. We compared monoculture and polyculture annual vegetable fields, 20- and 60-year-old peach [Prunus persica (L.) Batsch] orchards, and a bare field margin with 10- and 30-year-old hedgerows. We measured root dry mass, cumulative carbon (C) stock, and radiocarbon (Δ¹⁴C) to a target depth of 1 m, with orchard and hedgerow analyses restricted to 75 cm. The polyculture field had a higher observed mean C stock to 100 cm than the monoculture field, but radiocarbon differences between the fields were not supported. The C-stock comparison at 0–75 cm did not detect a difference between orchards. Δ¹⁴C was higher in the 20-year-old orchard at 20–50 cm. Both hedgerows had higher observed mean C stocks than the bare margin to 20 cm, while radiocarbon differences among the field margins depended on depth. Each management category was represented by one field or field-margin location, so management effects cannot be separated from site differences. Examining C stocks alongside bulk Δ¹⁴C across soil depths revealed differences among the sampled fields and field margins that overall stock comparisons alone did not capture.