An assessment of water quality impacts of managing and producing switchgrass for biomass

Kost, John
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Rathbun Lake is a 44.51 km2 reservoir on the Chariton River in Wayne County in southeast Iowa that provides drinking water to residents in Iowa and Missouri. Approximately 22% of cropland inside the watershed is used for corn and soybean production; water quality of the lake is threatened by herbicide and nutrient runoff, and its use as a flood impoundment is hindered by high siltation rates. To improve water quality, alternative land uses are being studied, including the production of switchgrass (Panicum virgatum) for biomass. The objective of this study was to assess the capacity for switchgrass managed for biomass production to control the loss of sediment, nutrients and agricultural chemicals. Three fields near Millerton, Iowa were selected for consistent slope and soil type. Sediment loss and runoff water quality were examined using a linear rainfall simulator. The study consisted of three treatments: newly planted switchgrass following soybeans (NSG), a thirteen year stand of mature switchgrass (OSG), and no-till corn following soybeans (NTC). Simulated rainfall rate was approximately 52 mm/hr. Duration of each simulation was 80 minutes. Period 1 runoff samples were collected in May, and Period 2 samples were collected late June through late July. Drought conditions prevailed from May through early June. Each runoff sample was evaluated for Nitrate + Nitrate (N+N), Total Phosphorus (TP), Atrazine (AT) and Metolachlor (MT). Total soil loss (TSL) and Total Water Loss (TWL) were calculated. Infiltration + Storage Capacity (ISC) was estimated. With the exception of AT in Period 1, NSG and OSG were more effective than NTC in minimizing TSL, TWL, and loss of N+N, TP and MT. TSL, TWL and TP loss were greater for NSG than for OSG for both periods. N+N loss was not different between NSG and OSG for either period. TWL was not different between NSG and OSG for Period 2. AT and MT losses were not different between NSG and OSG for Period 2. NTC demonstrated greater ISC than NSG or OSG in both periods. Switchgrass grown for biomass offers environmental benefits over NTC production in the Lake Rathbun watershed.