101
Miscanthus Production
80°11′ W) had been surface-mined, restored with mixed overburden, and
15 cm soil covering, fertilized, limed, and planted with mixed grass and
legumes 25 years earlier. It had been managed as mown forbs during that
time. Five replicate plots of 0.4 ha were planted to each of two types of
M. × giganteus – public and private from Mendel Biotechnology (unnamed
but likely Illinois and Nagara CVs). All plots were planted into a sod previously killed with glyphosate herbicide applied twice, fall and spring prior
to planting. Planting density was 12,300 plugs ha −1 . Even with a >20% loss
of plants this would still produce an appropriate plant density. Other plots
received two types of switchgrass, drilled into the killed sod. Yields of
switchgrass were 7.9 and 7.3 t ha −1 while the private M. × giganteus yielded
13.7 and the public 14.4 t ha −1 in year 5. The private CV increased yield
much more rapidly over years than the public, reaching 22 t ha −1 in year 3.
However, all measures of Miscanthus had large variation (SD ~50%, N = 5
plots) likely because all yield measures were based on random selections of
six plants, from large (0.4 ha) plots.
These M. × giganteus yields are very like those reported in the southcentral Virginia Piedmont region (~36°56′ N, 79°24′ W) in the same years by
Lee et al. (2018) and Battaglia et al. (2019). Switchgrass yields in West Virginia
(WV) were better than unfertilized soil of the Virginia (VA) portion of Lee
et al. (2018) studies, but lower than on fertilized plots. For switchgrass, six
0.21 m 2 quadrats were sampled on each of the WV switchgrass plots, but
again the SD was very large. A critical methodological difference is that the
studies of M. × giganteus coordinated by Lee et al. (2017) used a 4 m 2 sample
from the center of a plot of 10 × 10 m. With N = 4 for each different nitrogen fertilization level, the reported Standard Error of the Mean was much
smaller, closer to 10%. In the VA switchgrass study, there was a positive, usually large, response to added N each year. Their yields were measured by
complete biomass harvest on full plots of at least 0.5 ha.
A very useful European example is the work of Jeżowski et al. (2017) who
grew M. × giganteus on lignite mine spoils, with sewage sludge and mineral
fertilizer supplements. Three years prior to planting Miscanthus, a mix of
Medicago species was planted on the site which was roughly leveled. The
wet sludge (1 Mg per 5 × 5 m treatment plot) was applied in the autumn prior
to the Miscanthus planting and was incorporated into the soil to a depth
of ~30 cm. This corresponds to 400 t ha −1 wet wt, 80 t dry matter wt (DM).
Rhizomes were planted on 1 m centers, 25 per plot, in a randomized, three
complete blocks design. Treatments were D 0 = no addition, D 1 = addition of
~80 Mg ha −1 (DM) of municipal sewage sludge, D 2 = sludge + 200 kg ha −1 commercial fertilizer, D 3 = sludge + 400 kg ha −1 of commercial fertilizer. With a
composition listed as 13:19:16 for N:P:K, the added fertilizer makes a modest
N contribution of ~26 kg ha −1 to D 2 and ~52 kg ha −1 to D 3 . Total N for the sludge
was 43.4 kg Mg −1 DM (4.3%) for an applied rate of over 3400 kg ha −1 , although
most would be organic N. If this mineralizes at a rate of 2% per year it contributes all the N needed by the amount of biomass produced, over a long time.