• Plant samples are collected twice a year from all the GLBRC ten treatments to determine total carbon and nitrogen content of plant tissues. These are collected at peak biomass stage and at final harvest time.
• The purpose of the sampling is to estimate total carbon and nitrogen removed in biomass
• ANPP samples: annuals (G1-G4) – measure CN on the grain, stover, and weeds separately
• ANPP samples G5, G6, M3, and L2: measure CN on the target species (switchgrass or Miscanthus) and on a composited sample of all other species
• ANPP samples G7, G9, G10, M2, and L3: measure CN on the 3 most dominant species in each plot and on a composited sample of all other species
• Harvest samples in annuals: measure CN on grain from each main and microplot, also on corn stover
• Harvest samples in perennial plots – one composite sample is taken from each main and microplot
• Cover crop samples – measure CN on rye, Austrian pea, and a composited sample of all other species
• Samples are dried at 60^oC for 48 h and dried plant material is ground through a 1mm screen using a Christy-Turner 8” Lab mill.
• Triplicate subsamples (5.0 mg) of the sample are weighed with an electronic microbalance, packed into tin containers, and combusted at 1050^oC in an O₂ -enriched atmosphere.
• Combustion gases are analyzed for C and N with a thermal conductivity detector after separation on a Porapak Q column.