Patterns of soil organic carbon deficit in the Conterminous US

Abstract

Soil organic carbon (SOC) is integral to ecosystem stability, agricultural productivity, and climate regulation. The capacity of soils to stabilize additional SOC is highly uncertain, yet critical to understanding terrestrial ecosystem feedbacks to rising atmospheric carbon dioxide. Conceptually, the difference between a soil's capacity to sequester SOC (i.e., SOC saturation) and the current stock of SOC is the SOC deficit. To explore patterns in SOC deficit, we are using the newly collected, Rapid soil Carbon Assessment project (RaCA) database. The RaCA database contains more than 6000 pedons from the Conterminous US collected to 1 m of depth or more. Data for these pedons include SOC, soil inorganic C, total soil nitrogen, texture class, VNIR spectrum, and more, all of which are traceable and publically available from the USDA Natural Resources Conservation Service. The general goal of this paper is to test hypotheses about the roles of soil depth, land use and land cover, landscape position, and ecosystem type play in maximizing SOC content. We use existing methods to determine SOC saturation as related to soil texture classes, soil surface area, and statistical approaches. One specific goal is to determine the probability of SOC deficit in sequential soil horizons. For example, we test if SOC saturation is related to the saturation of proximal soil horizons and then explore land use and spatial patterns in the probability that SOC saturation is related to proximity. Understanding patterns in SOC deficit may be valuable to modelling terrestrial C dynamics in the Anthropocene.