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Application of Ion Exchange Resin Membranes to Nitrate Testing in the West

Greer, K.J., E. Bremer and T.J. Sievers . 2017. Western Nutrient Management Conference 12:101-105

Abstract

Introduction Resin membranes have been used since the 1960s to measure P supply from the soil. In the 1990s the Plant Root Simulator (PRS®) probe was invented to further refine a method to measure N mineralization from soil organic matter. The functional measurement of soil N supply during incubation has been applied to both in situ measures and in lab research studies. Extending the PRS® measurements of N intensity or flux to a meaningful number that a plant can utilize was accomplished using a version of the Barber Flux equations. Our paper attempts to elucidate the N flux approach used in the PRS CropCaster® as a means to measure and then extend the Nitrate from mineralized organic material to a potential uptake by crops Conclusions The PRS® N supply rate is a functional measure of the MOB engine. SOMC and residue C is altering the release rate of N. However the soil moisture and temperate can equally control the MOB turnover, respiration and Nmin. Respiration on its own can only be considered a proxy for N supply if the soil C sources have a very narrow C:N ratio and are highly labile. SOMC may have this narrow C:N ratio but may not necessarily readily mineralizable or labile. Residues from cover crops, composts and manures need to be assessed functionally to see if N mineralization will occur. Any interpretation of respiration rate alone should be considered with caution.