Graduate Thesis Or Dissertation
 

Nitrate and water under terraced dryland wheat production in Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pv63g363r

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  • Dry land agriculture using summer fallow is a common crop production practice in the Columbia Plateau region of eastern Oregon. Farmed-over level terraces are used to control surface water runoff and soil erosion. More than 70 percent of the average annual precipitation around Pendleton, Oregon (350 - 400 mm) falls as low intensity, long duration rainfall from September to March. Wetter soil zones typically occur above and below the terrace. These areas have a higher potential for crop production as well as for movement of chemicals to ground water and to surface water where seepage occurs. The extra nitrogen or water that could accumulate in these areas needs to be considered in managing these areas. The first objective of this study was to measure the distribution of nitrate nitrogen (NO₃-N) and water in relation to farmed-over level terraces, and infer potential solute flow patterns from changes in the measured distributions over time. The second objective was to make recommendations regarding management practices required for specific field locations to maximize crop production and minimize negative impacts on groundwater quality. Results indicate NO⁻₃ concentrations following harvest were < 4 mg kg⁻¹ of soil. Equivalent to soil solution concentrations between 27 and 20 mg L⁻¹ at 15 and 20 percent volumetric water content, respectively. Limited deep percolation of NO⁻₃ occurred below the root zone between harvest and planting. The NO⁻₃ concentrations below the root zone were < 1 to 15 mg kg⁻¹ following the summer fallow period. In August 1993, evidence exists that shows N applied fertilizer moved out of the surface 0.3 m and deeper into the profile. The redistribution of NO⁻₃ in the terrace channels of transects 1 and 2 strongly support this. Soil profiles that contain high residual concentrations of NO₃-N during the fallow period increase the potential for NO₃-N leaching below the root zone. Unusually heavy precipitation during normally dry periods or above normal winter precipitation increases the potential for NO₃-N leaching below the root zone.
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