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Using the Late Spring Nitrate Test to Reduce Nitrate Loss within a Watershed

USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011

View larger version (43K): [in a new window]   Fig. 1. Location of Walnut Creek watershed (WCW) within the state of Iowa (inset), and the location of the stream, district drains, discharge gaging stations, control subbasins (CN1 and CN2), and treatment subbasin (TR1) within WCW.

View larger version (43K): [in a new window]   Fig. 2. Late spring nitrate test (LSNT) treatment fields within Subbasin TR1 of Walnut Creek. Letters within each field identify the crop rotation starting in 1997. Lowercase letters indicate years when the LSNT was not followed for applying N fertilizer.

View larger version (27K): [in a new window]   Fig. 3. Nitrate concentration in drainage from the control (CN1 and CN2) and treated (TR1) subbasins.

View larger version (37K): [in a new window]   Fig. 4. Nitrate concentrations in the treated subbasin (TR1) minus the concentrations in the control subbasin (CN1) during the late spring nitrate test (LSNT) treatment period and the fitted quadratic model with a Lag 1 residual component and its 95% confidence limits. Concentrations from the two subbasins are significantly different when the confidence limits do not include the 0 difference line.

View larger version (36K): [in a new window]   Fig. 5. Nitrate concentrations in the treated subbasin (TR1) minus concentrations in the control subbasin (CN2) during the late spring nitrate test (LSNT) treatment period and the fitted quadratic model with a Lag 1 residual component at its 95% confidence limits. Concentrations from the two subbasins are significantly different when the confidence limits do not include the 0 difference line.