2017 ASHS Annual Conference

Carbon dioxide release from microbial respiration in the soil is a potentially important process to measure and predict availability of mineralized nitrogen; an essential compound not measured in routine soil tests. A primary objective was to determine if there is sufficient biologically produced nitrogen to credit towards estimated crop needs of a representative smallfruit example. This five year field study assessed soil fertility and health in eight commercial, organic highbush blueberry fields (Vaccinium corymbosum L.) in New Jersey. Carbon dioxide production from microbial life in the rhizosphere was measured with the Solvita® CO₂ aerobic respiration test. Average annual CO₂ values from 2013-2015 for five organic blueberry fields was 49.7, 53.8, 58.6 and 61.8 CO₂ ppm per 40 gram dried sample, respectively. These values are categorized as 4.0 on a 0-5 scale with 4 being the best and 5 excessive. These soils were characterized as having medium to ideal fertility compared to marginal ratings for 46 conventional blueberry soils that reached only 14.1 CO₂ ppm or less. The main distinction of organic perennial cropping was no tillage which left soil undisturbed along with standard practices of applying composted amendments and excluding synthetic pesticides. Similarly, native pine forest soils with a wild blueberry understory adjacent to the conventional fields had as high biological respiration as the organic cultivated blueberries. This microbial activity indicates sufficient organic matter is available under favorable soil health conditions to provide a seasonal and dynamic return of nitrogen ranging from 25 to 50 lbs per acre.