Comparative Analysis of Greenhouse Gas Emissions from Miscanthus and Switchgrass Grown on Marginal Land.

Perennial grasses such as, Miscanthus (Miscanthus × giganteus) and switchgrass (Panicum virgatum), are considered superior for the bioenergy production than annual grasses such as, maize (Zea mays) and sorghum (Sorghum bicolor) because of their ability to produce high biomass with relatively low input of nitrogen (N), phosphorus (P), and potassium (K). However, the relative contribution of these perennial and annual crops to greenhouse gas (GHG) emissions, particularly on P- and K- deficient soils is not known. The objective of this study was to compare GHG emissions from replicated side-by-side trials of Miscanthus, switchgrass, mixed native prairie, continuous maize, and continuous sorghum in 2013 and 2014. Except mixed native prairie, all crops had N treatments that included unfertilized and fertilized treatment (100 kg N ha^-1 yr^-1 for Miscanthus and switchgrass and 150 kg N ha^-1 yr^-1 for maize and sorghum). Miscanthus and switchgrass had additionally P–K treatments, switchgrass was grown on plots that historically either received P–K treatment (75–400 P–K kg ha^-1 yr^-1) or kept unfertilized and Miscanthus was either fertilized with a rate of 30–300 P–K kg ha^-1 yr^-1 or kept unfertilized. A weekly assessment of N₂O, CO₂, and CH₄ in situ fluxes commenced in 2013 and 2014 from April to October. Over two years of trials, the biomass yield of Miscanthus, sorghum, switchgrass, maize, and mixed native prairie was 24.9, 12.3, 10.8, 9.5, and 6.1 Mg ha^-1. Biomass yield of Miscanthus and switchgrass did not change among P–K treatments reflecting that these crops have the potential to produce high biomass even at low soil P and medium K test levels. The amount of total precipitation received after N fertilization event had large influence on daily N₂O fluxes measured at next sampling events and this effect was further exacerbated with PK fertilizer application to Miscanthus and switchgrass. In contrast to daily N₂O fluxes, there were no differences in temporal trends in daily CO₂ and CH₄ fluxes, soil moisture content, and soil temperature among maize and sorghum crop and among different N and PK fertilizer application treatments.