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Predicting Biosolids Application Rates for Dryland Wheat across a Range of Northwest Climate Zones

Sullivan, Dan M., Bary, Andy I., Cogger, Craig G., Shearin, Todd E.
Communications in soil science and plant analysis 2009 v.40 no.11-12 pp. 1770-1789
Triticum aestivum, soil amendments, nitrogen fertilizers, biosolids, application rate, prediction, plant response, grain yield, protein content, nitrogen, nitrates, sewage sludge, agricultural soils, dryland farming, Washington, Oregon
We evaluated dryland wheat (Triticum aestivum L.) response to biosolids applications in the inland Pacific Northwest and compared agronomic application rates predicted from yield curves with those predicted from Extension guidance. We applied biosolids rate treatments during the fallow year in 10 on-farm experiments and determined grain yield, protein, and postharvest soil nitrate. Nitrogen (N) rates were calculated from Extension guidance and compared with biosolids agronomic rate estimates based on yield regressions generated for each site. Eight of the 10 sites had quadratic yield responses. The agronomic biosolids rate at the responsive sites averaged 315 kg ha-1 more grain than the farmer inorganic N rate. At responsive sites, a mean biosolids application rate of 4.7 dry Mg ha-1 (226 kg total N ha-1) was required for 95% of maximum grain yield. Results showed that Extension fertilizer guidance together with calculations for biosolids available N gave reasonable estimates for biosolids application rates.