I am little surprised to see Jatropha as the worse case, this is a plant that thrive in semi arid climate, so my guess is that it doesn't require watering or irriguation, also biodiesel require not water in processing the oil of the seed, contrary to ethanol that requires tons of water in the process. Also I don't see palm tree in their comparison. Palm tree producess more biodiesel than any other crop altogether, so why it is not included in their study. Also I wonder how they calculate the amount of water diverted. If you plant a tree you divert a lot of water because the tree need water so store it in its roots, ok but trees do so much to protect and improve the soil, to protect from soil erosion, trees with their deep roots bring nutriement from yards bellow to the surface of the ground, they regulate climate and moisture, they provide storge of CO2 and material for construction. So it is not like this water was wasted.

Thats absolutely true
http://www.enjoygreencar.com/

Water utilization efficiency becomes critical when a crop is irrigated; however, most of these crops, except for rice, are not normally irrigated. In most locations, they are dryland crops supplied with water by rainfall and snowmelt. Because of the inefficiencies of photosynthesis and the need for plant cooling, most water absorbed by a plant is respired and sent back out into the atmosphere.

Most of the new ethanol plants recycle their processing water, reducing input needs and cost of water treatment. Although the total water quantity may be high, it's not new water all the time, but mostly reused water.

Humans have relied on annual plants to concentrate nutrients for them. Annuals are disturbance plants requiring high inputs and fertility. Perennials are low disturbance, low fertility, low input plants. Certainly for energy production, perennials are the way to go.

I like the idea of using a by-product like corn stalks.

These clowns left out kudzu and switch grass.

It seems all these "researchers" have an ax to grind.

I don't like the idea of using corn stalk,

to leave corn stalk on the ground is absolutely essential to protect the soil from erosion and return nutriement to the soil. If you don't be prepared to the return of dust bowls in the midwest like in the 30s

Kudzu is one of the most invasive plants in the world and there is an Early Detection Rapid Response alert in effect for its arrival in Canada.

It's too bad we spent all that money building sewage treatment plants in the Midwest, I wonder if it would not be better to instead ship it to corn fields and fertilize them with natural sewage fertilizer. I wonder what the comparative emissions are of transporting sewage versus making and transporting solid conventional fertilizers.

After all, a good portion of that original fertilizer spread on corn fields makes its way to the sewage treatment plant so it is like recycling!

Annuals mine the soil, perennials generate soil. There is a zero sum involved: a plant can concentrate energy, as biomass, either in a seed head or underground root mass, but it can't do both at the same time. Concentrating energy in a seed head is an intensive process. If cellulosic biomass is desired, the worst way to go about it is to grow annual plants to produce it. Using corn stover for cellulosic feedstock is a bad idea, since that biomass is needed to go back into the soil to replace what the plant has taken out. Present state of the art farming methods try to keep as much "trash" as possible in the soil to reduce soil erosion.

Switchgrass, and other C4 photosynthesis pathway grasses like miscanthus, big bluestem, or sugar cane, (commonly called "warm season" grasses), have higher photosynthetic and water utilization efficiency than the common cereal grain C3 annuals like wheat, rice, barley, etc. Corn is a C4 annual, which is why so much of it is grown. It's a more efficient plant. Switchgrass is a long-lived perennial. It would not require replanting on ten year intervals, like sugar cane.

Plant sterility is preferable for a cellulosic biomass feedstock plant. This is one reason Miscanthus giganteus, a naturally occurring sterile hybrid, is such a prolific biomass producer. Since plant phenology is primarily based on growing-degree days, i.e. accumulated heat units, a winter hardy plant like switchgrass can be moved far north of a particular cultivar's point of origin, resulting in virtual sterility, since the more northerly location would not accumulate sufficient heat units to trigger seed set, but would produce more biomass from the longer day length. REAP-Canada has discovered the value of this phenomenon, producing greatest switchgrass biomass yields in Quebec from seed originating in southern Illinois.

There seems to be lots of land that we could grow switchgrass on, if there was a market for the biomass. One of the main reasons for the dust bowl was tilling that dried the soil. If you don't till, you don't dry. Leaving the bottom stem and roots of the corn plant in place and no till farming could help.

Kudzu dies back to the ground in winter but resprouts from roots. It has made it to Oregon and New Jersey.

Water is definitely an issue for biofuel production. That is why no one will see biofuel crops grown in Saudi Arabia any time soon. Biofuels can be seen as solar energy bound chemically through photosynthesis, a process that occurs in aqueous media within the cell. Because of this only certain climatic zones are suitable for biofuels. In other places wind, wave, or solar thermal or photovoltaic are options to get the energy which comes from the big natural nuclear fusion reactor - the Sun.

Treehugger, as a resident of Michigan I have to point out that farmers here have been making sugar from sugar beets for a long time.

http://www.michigansugar.com/

Granted, I've no idea how economical it is or what the ROI is, but they're doing it.

Once again the Greens easy and ready answers are discovered to have major warts, in practice. Their ill-considered, politicized patent remedies don't work, or have major unexpected problems to them, that are only recognized after $ billions in subsidies.

Windmills, Solar, 1st generation Biofuels, 2nd generation Biofuels, Biodiesel, all turn out to have major drawbacks, and pollution effects of their own, often worse than conventionql energy generation.

Greens exclude the only real renewable that works, Hydro-electric power, that the Greens have somehow decided is not a "genuine Green" renewable. Apparently rain falling amd flowing into rivers and trapped in reservoirs is not a natural, recurring effect, to them.