Root:Shoot ratios
-----------------
Miscanthus S:R ratio: 2.57 as per Mann et al. 2012
http://onlinelibrary.wiley.com/doi/10.1111/gcbb.12039/full
This implies root:shoot ratio of 0.389

Other sources put the root:shoot ratio at close to 1. See,
for example, Heaton et al. 2010.
DOI: 10.1016/S0065-2296(10)56003-8

Switchgrass R:S ratio, 0.350 taken from Frank et al. 2004
https://dl.sciencesocieties.org/publications/cs/abstracts/44/4/1391

Not a very thorough search, but good placeholder values.

Dry fraction
------------
Set to 1.0 for both grasses, assuming yields are proved in bone-dry tons.

Harvest index
-------------
Set to 0.9 for both grasses, lacking data. Just a placeholder.
