Estimating Seasonal N Mineralization from Short-Term CO2 Evolution.

Accurate prediction of the contribution of soil organic matter (SOM) to seasonal plant-available N has proved problematic. Consequently, fertilizer N recommendations often do not accurately account the contribution of soil to in-season N availability, resulting in over fertilization. Microbial respiration upon rewetting of air-dried soil has been theorized as a viable biologically-based estimator of long-term net N mineralization. Lab incubations were performed on California agricultural soils, which varied widely in texture, management, and other physiochemical properties. This biologically-based test explores the coupling of short-term (24-hour) microbial respiration to long-term net N mineralization. Preliminary analysis shows no significant correlation between cumulative respiration and N mineralization. This biologically-based test did not offer increased accuracy of prediction over any studied chemical assay. Additional research will investigate interactions between various soil characteristics, as well as incorporating field validations or lab work.