The most efficient plant is probably genetically engineered algae, which is where most of the research work on biodiesel is going on today.
Soybean oil, however, is more or less a byproduct of milling the soybeans into cattle feed.
I notice that this article plays fast and loose with the difference between biodiesel, which actually works and doesn't necessarily have to drive food prices up, and corn-based ethanol, which gives lower mileage in engines not engineered for it (= most of them) and is guaranteed to drive food prices up.
The reason I said the writing was a piece of biased trash. All seed even peanut is put under hydraulic pressure and the oil comes out, have read about the alga and the process a VT, professor has patented but they both seem to have a way to go.
Planting soybeans, or any other legume that I know of, is a good way to ‘fix’ nitrogen in the soil. In some areas, it makes a nice winter cover to get the fertilizer benefits and to hold the soil in place.
Well, ethanol does work, what you said is something of a misnomer.. Ethanol policy based solely on corn, is doomed to failure for all the reasons mentioned above. Sugar ethanol, switch grass, etc, and any combination not solely relying on corn, however is an excellent idea. Anything less shows one to be beholden, financially or psychologically, to oil interests..
Energy policy needs to be diverse and open to multiple sources to fuel our energy needs, not bet the farm on one single source...