Table 1.
Nitrogen mass balance for switchgrass at the MI site.
Table 2.
Inorganic N concentrations by site and sampling timea.
Fig 1.
Potential switchgrass root ANF rates from two sites (MI: Kellogg Biological Station in Michigan, USA and WI: Arlington Agricultural Research Station, Wisconsin, USA) across four time periods.
Roots were sampled from plots with a range of N fertilizer addition: A. unfertilized, B. 56 kg N ha-1 yr-1, and C. 196 kg N ha-1 yr-1. Note that the senescence period has a different scale to accommodate the much higher rates during that time period.
Fig 2.
Soil potential ANF rates from two sites (MI: Kellogg Biological Station in Michigan, USA and WI: Arlington Agricultural Research Station, Wisconsin, USA) across four time periods.
Soils were sampled from switchgrass rhizospheres grown with a range of N fertilizer addition: A. unfertilized, B. 56 kg N ha-1 yr-1, and C. 196 kg N ha-1 yr-1.
Fig 3.
Net N mineralization rates, measured via 28-d aerobic incubations, during four time periods.
Best-fit regression lines are shown where slopes were significantly different from 0. Soils were sampled from switchgrass rhizospheres at two sites (MI: Kellogg Biological Station, Michigan, USA and WI: Arlington Agricultural Research Station, Wisconsin, USA) and 3 fertilizer levels (unfertilized, 56 kg N ha-1 yr-1, and 196 kg N ha-1 yr-1). MI Post-fertilizer: y = 0.40*(x+1)^0.14, p = 0.04; MI Peak biomass: y = 0.07*log(x+1)+0.25, p = 0.002; MI Senescence: y = 0.04*log(x+1)+0.31, p = 0.03; WI Post-fertilizer: y = 0.002*x+0.299, p<0.02; WI Peak biomass: y = 0.127*(x+1)^0.15, p = 0.03; WI Senescence: y = 0.0012*x-0.015, p = 0.004.