... sooner or later, the fossil fuels that power them will diminish and make them too costly to own before going away completely. When that happens, there had better be some other plan for powering the farm equipment we depend on to plant, grow and harvest our food, to say nothing of the military vehicles and aircraft we depend on to keep the world safe for freedom and democracy. ...
I agree that in many applications, high energy storages density, liquid fuel may be essentially necessary, but do you know than ethanol in a gasoline IC gives slightly more HP than gasoline does? * In Brazil new cars have a window sticker that tells the Km/ liter, the horse power, and (full tank range, I think) for both fuels as almost all new cars are now "flex fuel."
The alcohol range is only about 70% as great as gasoline, but that makes little difference to small airplanes used as "crop dusters" - they must soon and for more of the pesticide etc. they are spraying, and the slightly greater HP and lower per hour flown cost of ethanol have made many, if not most, crop dusters, alcohol fueled now.
A little more than decade ago, Scientific American, I think it was, listed the 50 most important inventions /technologic developments in the prior year. Two were in the field of aviation - one was Brazil's development of the alcohol powered crop duster.
I think conversion of no-spark, high-compression heat ignition diesel to either gasoline nor alcohol is not very feasible but as alcohol gives more power for plowing than gasoline does and gasoline tractors do exist, I think getting tractors off oil is very feasible.
* And that is just in the SAME flex-fuel IC engine. If the engines is designed for alcohol only, higher compression can be used for even more power, as the "octane rating" is greater - alcohol not only burns cleaner but is less prone to "knocking" as well as slightly CO2 negative, (not a dominate source of CO2 release), completely renewable, and a very economically completive form of solar energy when oil is at least ~ $75 per barrel as it normal is and will be again before long..
BTW, I think the Amish definitely do have a point. They respect the earth and live sustainably with it and others of mother nature's creations. When visiting my daughter who lives in Malvern PA, we usually get up early on Saturday to buy their produce a few miles from her condo. By 10 AM it will all be gone and they are packing up the buggy for the drive back to the farm. There the "top soil" farmed for 150 or more years is about a foot thick - would be deeper but that is as deep as the horse team can plow the fallow field's "green manure" under. They are very kind to the earth worms in a symbiotic relationship. I think they even fish with nets, not modern metal fish hooks. One thing they usually do is send a late teenage child off to live with non-plain folks in a town for about a year. - More than half return to their simple way of life. This serves to keep it strong and gives some population control. I admire them.