Zinc Fertilization of Wheat in a Low-Rainfalll Area of the Inland Pacific Northwest.

Soils in north-central Oregon frequently test below 0.5 mg kg^-1 for DTPA-extractable Zn.  Consultants and researchers agree these levels are low, but questions about the likelihood of a plant response to Zn fertilization warrant attention.  Additional concerns about the effect of available P on Zn nutrition also need to be addressed.  Relevant field experiments, conducted during the last ten years, utilized treatments that consisted of  two Zn rates (0 and 5 kg Zn ha^-1) applied in factorial combination with 0, 7.5, and 15 kg P ha^-1).  Treatments were arranged in a RCB-4 design on deep silt loam soils.  Soil pH was slightly-to-moderately alkaline in the top 30 cm of the soil profile.  Organic matter content was low (9 to 11 g kg^-1).   The CEC was approximately 12.5 cmol kg^-1, and sodium bicarbonate-extractable P levels were less than 12 mg kg^-1.  Crop-year precipitation ranged from l80 to 300 mm.  Treatments were applied to spring and winter varieties of wheat (Triticum aestivum L.) using a customized, no-till drill that placed fertilizer in close proximity to the seed.  Plant samples were collected from plots of wheat after the first node was detectable just above the soil surface.  Grain harvest was accomplished using a small-plot combine.  Grain yield and test weight were adjusted to 100 g kg^-1 moisture content.  An interaction between P availability and Zn uptake was demonstrated with data from this research.  Yield response was observed in one of five field experiments.