Although agricultural influence on sediment runoff is well known, determining what sources of sediment contribute most to stream impairment has remained challenging in agricultural watersheds across the world. Therefore, methods to distinguish the sources of sediment in streams are warranted, particularly methods that incorporate information on anthropogenic practices that affect sediment runoff. In this study we examined how variations in conservation practices contributed to unidentified sources of sediment in an agricultural watershed, where 49% of sediment was sourced from agricultural fields that were assumed to have little erosional runoff. We found that variations in the way no-till agriculture is practiced significantly affected estimates of erosion in the watershed and also led agency managers to overlook sources of sediment in the watershed. In doing this research, we provide a methodological framework that may be useful to researchers who are attempting to identify sources of sediment erosion in watersheds impacted by variations in agricultural conservation practices.
A variety of agricultural conservation trends have gained and lost favour throughout the years, with farm bills in the United States often influencing which conservation practices are implemented. This paper explores the consequences of a set of conservation techniques loosely defined as “no‐till agriculture,” focusing on their implementation and adoption since 1985, at which point such approaches began to be explicitly encouraged under US Farm Bill soil conservation mandates. We begin by noting a core contradiction that has characterized these approaches in the Fifteenmile Watershed of Wasco County, Oregon, where despite high rates of farmer enrollment in no‐till programs, both no‐till agriculture and sustained tillage have led to the increased use of herbicides and sustained sediment runoff. Using a critical physical geography framework that integrates intensive physical field data collection, spatial analysis, social surveys, and interviews, we address the biophysical and social factors collectively driving changes in herbicide use and variable erosion estimates. We draw particular attention to how farm bill support for no‐till has enrolled farmers in a vaguely defined and underregulated conservation practice that may ultimately undermine environmental quality.
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