Abstract:
Lack of growing season precipitation and the temperate climate in north central Oregon
pose challenges to growing spring wheat crops. Phosphate and sulfate fertilization can
improve early growth of spring wheat in this region and soil testing aids in determining
rates of fertilization. In this study, anion exchange membranes (AEM) were used to
assess phosphorus and sulfur supply rates in four, minimally-tilled, annually cropped
spring wheat fields in north central Oregon. To determine the validity of AEM in this
region, uptake of P and S by hard red spring (HRS) wheat was correlated with soil supply
of P and S as predicted by AEM. I found that in low soil water content and cool soil
temperature conditions, AEM did not accurately measure plant available P and S. Unlike
plants, AEM are static instruments that cannot measure plant available nutrients when
soil conditions limit mineralization and diffusion of plant nutrients. I also found that
three consecutive years of drought across the study sites has led to P and S quantities sufficient for maximum yield potential of HRS wheat without fertilization. These results
suggest that growers in north central Oregon may not necessarily need to fertilize wheat
crops following a drought and that AEM may provide inaccurate information regarding
soil nutrient status.
