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The proposed methods for this study are to apply four treatments of 15N enriched urea fertilizers to 100m2 plots at 10 sites in western Oregon and Washington over two years (five sites each year). Above and bellow ground ecosystem component will be sampled to determine d15N concentrations after one year, and compared to background d15N derived from a control plot to quantify the amount of fertilizer nitrogen in each component one year after application. The four treatments will be:
1.)Untreated urea pellets
2.)Urea+NBPT: Urea pellets coated with N(n-butyl) thiophosphoric triamide, commercially available as Agrotain. The NBPT binds to the active site of the enzyme urease, inhibiting the enzyme’s capacity to catalyze the hydrolysis of urea.
3.)Urea CUF: Urea pellets coated in a boron solution that inhibits urease and acts as a binding agent for secondary nutrients like Phosphorous in the commercial variety Arborite.
4.)ESN urea: Polymer coated pellets of urea commercially available under the brand Agrium designed to delay urea release to the soil by creating a permeable physical barrier that breaks down in time.
The results of this study are expected to assists foresters in selecting the best urea formulation for Douglas-fir fertilization in western Oregon and Washington.