I'm trying to compile the root depth of some grasses. I'm not talking about the depth of reproductive rhizomes, but the depth of feeder roots. This info is relevant in regards to nutrient recovery, drought resistance, and building up the soil (adding carbon back to the soil, supporting the soil microbial food web, keeping the earthworms happy).

----- info sources -----

I'll start with what I found so far. Some of the info comes from the "Plant Materials Centers" (mostly Bismarck, ND) of the National Resources Conservation Service (formerly Soil Conservation Service) of the USDA:

http://plant-materials.nrcs.usda.gov/centers/

Some info comes from USDA plants database plant guides:

http://plants.usda.gov/java/factSheet

And some info comes from the Land Institute:

http://www.landinstitute.org/

--- list of ornamental, conservation, or livestock grasses ---

Panicum virgatum (Switchgrass): up to 9 feet deep

Andropogon gerardii (Big Bluestem): up to 12 feet

Schizachyrium scoparium (Little Bluestem): 5 to 8 feet

Nasella (Stipa) viridula: up to 10 feet

Leymus angustus (Altai Wildrye): up to 10 feet

Thinopyrum intermedium (Intermediate Wheatgrass): about 6 ft