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

D. B. Jaynes*, D. L. Dinnes, D. W. Meek, D. L. Karlen, C. A. Cambardella and T. S. Colvin

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



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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.

 


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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.

 


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Fig. 3. Nitrate concentration in drainage from the control (CN1 and CN2) and treated (TR1) subbasins.

 


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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.

 


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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.

 





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