Surface water quality impacts from organic versus conventional agricultural systems

Agriculture is integrally intertwined with water, yet we have little information about how the different approaches to growing food influence water quality. Food production through different strategies is driven by economic and environmental concerns. Organic agriculture has increased for several decades and is projected to continue. Here, we conducted a literature synthesis of paired field studies documenting water quality differences from conventional and organic agriculture of terrestrial row-crops. Using the 37 papers that met our criteria, we compiled water quality parameters and calculated the percentage change between conventional and organic treatment paired comparisons. This synthesis revealed that 79% of the 14 nutrient, soil loss, and runoff parameters with at least five paired comparisons more often showed either improvement or no difference with organic. Specifically, nitrogen and overall soil losses were reduced in organic systems; however, soil loss outcomes were strongly influenced by tillage practices, and fertilizer type could change whether an organic field experienced greater or lesser nitrogen losses. Losses of phosphorus and carbon generally increased under organic agriculture, except for total phosphorus in runoff. Paired-field trial comparisons were rare in the literature and highlighted the need for additional studies, consistency in the parameters measured, and sufficient data collected to account for variation in fertilizers, tillage intensity, soil types, and topography, among other parameters. As publications comparing conventional and organic soil quality increase rapidly, studies of water quality lag, leaving open the potential for a shift in agricultural approaches to have unintended consequences for this essential resource.