Graduate Thesis Or Dissertation
 

Ion exchange membranes and agronomic responses as tools for assessing nutrient availability

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  • Winter wheat is commonly grown in rotation with leguminous and non-leguminous crops in the Willamette Valley. For agronomic, economic, and environmental reasons it is important to understand the influence of previous crops on availability of N and other nutrients. Objectives of this study were: (1) to evaluate the effects of long-term rotations on winter wheat response to N fertilizer, and (2) to evaluate the use of Plant Root Simulator™(PRS) probes for measuring soil N mineralization and N availability to winter wheat. Field experiments were conducted over three growing seasons in plots of `Stephens' soft white winter wheat at Hyslop farm. Plots receiving 0, 50, 100, 150 and 200 kg N ha⁻¹ at Feekes GS 4 were sampled to determine above ground N uptake, grain yield, and grain protein. In spring 1998, PRS probes were placed in 0 kg N ha⁻¹ plots and removed at one-week or two-week intervals. In autumn 1998, probes were placed in unfertilized plots and removed at 1-week, 4-week, and 8-week intervals. Probes measured the availability of NH₄⁺-N, NO₃⁻-N, K⁺, Ca²⁺, Mg²⁺, and P0₄³⁻-P. Grain yield and N uptake were greater for wheat following clover as compared to following oats. Three-year average fertilizer equivalent values calculated from N uptake and grain yield data were 44.5 kg N h⁻¹ and 49.0 kg N h⁻¹, respectively. The similarity of these independent measurements suggest that differences in N availability were the primary reason for the rotation effect. PRS probes also detected rotational differences in N availability. Average N recovered by probes sampled at 1-week intervals indicated that there was 63% as much NO₃⁻-N available to wheat following oat as compared to clover. Wheat recovered 64% as much N following oats as compared to clover. This suggests that PRS probes are an effective method for predicting relative amounts of plant available N. PRS probes also detected rotational differences in plant available potassium. Agronomic responses are useful for assessing the availability of nutrients that are limiting plant growth. PRS probes, on the other hand, are effective for assessing the availability of both limiting and non-limiting nutrients.
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