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Agronomic biosolids application rates for dryland wheat across a range of northwest climate zones Public Deposited

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  • Predicting agronomic rates is important to derive optimum economic and environmental benefits from biosolids fertilizer applications. We conducted this research to 1) evaluate dryland wheat response to biosolids applications over a range of climate zones in the Pacific Northwest and 2) compare agronomic application rates predicted from yield curves with those predicted from published extension guidance. We applied a range of biosolids rates during the fallow year in ten on-farm dryland wheat experiments located in five counties in central and eastern Washington and in one county in north-central Oregon. Grain yield, protein, and post-harvest soil nitrate were determined. Recommended nitrogen rates for each site were calculated from Extension nutrient management guidance, and compared with biosolids agronomic rate estimates based on 95% maximum yield from the regressions generated for each site. Eight of the ten sites had quadratic yield responses. The two non-responsive sites had high pre-application levels of soil nitrate-N. Protein response was linear at most sites, while soil nitrate accumulation was variable, with the greatest increases at the least responsive sites. Field agronomic rates were within 20 lb N/acre (0 to 0.6 dry tons biosolids/acre) of recommended rates at six of the 10 sites. Greater differences at the other sites resulted from leaching, drought, or high pre-application soil N. At the eight sites that responded to N application, a median biosolids application rate of 2.2 dry ton/acre (approx 200 lb biosolids total N per acre) was required for 95% of maximum grain yield. This research demonstrated that the use of a WA fertilizer guide together with a PNW worksheet for estimating available N from biosolids gave reasonable estimates for biosolids application rates. We suspect that one of the benefits of biosolids for dryland wheat production is that wet crop years increase both grain yield potential and N mineralized from biosolids.
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  • Sullivan, D., A. Bary, and C. Cogger. 2007. Agronomic biosolids application rates across a range of Northwest climate zones. p. 188-193. In: J. Hart (ed) Proc. Western Nutrient Management Conference. Vol. 7. Mar 8-9 2007. Salt Lake City, UT. This conference paper preceeded refereed publication in Communications in Soil Science and Plant Analysis 40:1770-1789 (2009).
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  • Salt Lake City, Utah, USA
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