what is the productivity of recently planted fuel producing crops, preferably in the ratio to the fuel consumed by growing these plants?
how much fossil fuel is currently burned to produce a gallon of pure alternative / 0 fossil / diesel?
Any varietes producing more than consuming, recently?
you can include the crops producing ethanol, too.
briquettes.... i havent seen a tractor burning briquettes recently.

Univ. of Minnesota researchers say ethanol from corn provides 25% more energy a gallon than is required for its production, while soybean biodiesel generates 93% more energy

From Business Week magazine 11/13/2006: For each unit of energy consumed in planting, fertilizing, harvesting and distilling, ethanol yields about 1.5 units. At 3.0, biodiesel's energy balance is even better. But the Holly Grail is so-called Cellulosic ethanol made from woody crops and plant waste. It has an energy balance of up to 36.

Algae produces 100 times more oil per acre than traditional food oilseed crops (250 times than soybeans). Recent (early 2007?) studies using a high fat species of algae (which cost around $1200 per pound) show that only 0.3% of the land area of the US could be utilized to produce enough biodiesel to replace all transportation fuel the country currently utilizes. {I forgot to write down where I read that.}

Bio-diesel from recycled cooking oil produces 5.5 times the energy used to create it.

In Europe, a typical rapeseed (Canola in the US) farmer can produce 84 gallons of biodiesel per acre planted. Snohomish County, Washington state farmers averaged 158 gals of biodiesel per acre of canola. Soybean oil yields only 48 gals. per acre.
Biodiesel from Chinese Tallo Trees - Classified as a pest-invasive species in much of the US, the trees yield 10 times more oil per acre than soybeans.
Sept 2007 Biodiesel from jatropha trees - can be grown in soil and dry areas not suitable for food crops. Cloned seedlings (as used by Lee County, Florida in their test plot) have an estimated cost per barrel of $43 which edges out every single crop in the US. Soybeans are $122 per barrel and sugarcane is $45.
Biodiesel from peanuts - There are about 24 peanut varieties being scrutinized to produce biodiesel. Traditionally grown peanuts can produce approximately 120 to 130 gallons of biodiesel per acre.
Check out biodiesel from poisonous jojoba weeds. It may be choking lakes in East Texas, Western Louisiana.
The above may not exactly answer your questions but I hope it helps.