Gas samples and soil data were taken from two adjacent sites. One site used conventional farming methods and the other used organic methods to grow crops. These sites were managed by the lab of Lori Hoagland of Purdue University. Each site contained 3 plots each with one replicant of soybeans and tomatoes. Gas samples were collected into vacuum evacuated vials every 15 minutes for a total of 60 minutes and 5 samples per replicant at each sample location. Gas samples were taken roughly every week from April 19th to November 8th in 2014 and June 11th to September 21st in 2015.
Gases were measured using food pans modified for the purpose.1 Samples were run immediately upon return to the laboratory for analysis by gas chromatography (GC) using an Agilent 7890 GC equipped with a FID detector, a TCD detector and a micro ECD (Santa Clara, CA) . A PAL model 120 autosampler upgraded for headspace analysis (Quantum Analytics, Foster City, CA) was used to inject samples using 20 mL vials with magnetic caps (Agilent, Santa Clara, CA catalog # 5188-2759). The GC was further customized (Custom Solutions Group, Katy, TX) by the installation of two pneumatically actuated 10 port gas sampling and backflush-to-vent valves, and a 6 port series-bypass valve on Valcon E rotors, and a switching solenoid valve for purge of valve loops between injections. Four columns were installed; a HayeSep N 80/10 mesh micro-pack stainless steel, a HayeSepQ 80/100 mesh micropack stainless steel column, a HayeSep N 80/100 mesh silcosteel and a HayeSepQ 80/100 mesh micropack silcosteel, all with the dimensions of 4’ x 1/16”. Helium was used as a carrier gas and make-up gas except for the ECD which used nitrogen as make-up gas. Injector temperature was 100° C and flow rate was set at 40 mL min-1.
Soil temperature and moisture were measured using Spectrum Technologies model 1650 dataloggers. Data was taken from 3 WaterScout SM 100 soil moisture sensors and one soil temperature sensors. Separate data loggers measured the soil moisture and temperature at east and west locations at each site (organic and conventional). Gas and datalogger data was taken from April to November in 2014 and June to September in 2015.
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We would like to acknowledge the hard work of all involved with this project including Alex Torline, Emily Gunter, Michelle Schlup, Liz Strauss, and Jamie Wise. We would also like to acknowledge the work of Nathan Linder and the MEIGS Agricultural Center.