I think that the main source of confusion about fossil fuels and agriculture is that so many equate energy with fossil fuels. They aren't the same thing. You can string together a series of factoids that purport to show that food is oil, but all you have really shown is that food is energy. Duh!

I became fascinated with the connection between our food supply and energy when I first learned of the problems that North Korea was having feeding itself. (see here). This data showed me something amazing about modern society, we don't live in the information age, we don't live in the industrial age, we live in the agricultural age. Without food, we have no industry or information. Unfortunately many don't understand this. Nor do they understand that today the modern farming system is merely a means to turn petroleum into food, via mechanized planting and harvesting, and the use of petroleum based insecticides and fertilizers which consume huge amounts of energy in their manufacture.

Notice the instant slide from energy to petroleum, as if they were two words for the same thing. They aren't. Energy is needed to produce food for 6 billion people, but petroleum is not needed. It's just cheap and abundant in this era, something that was not true in the past and may not be true in future.

This demonstrates the second major gaffe in the above line of reasoning. We do live in an age of information and industry. We (thankfully) do not live in the agricultural age. A little information about energy, chemistry, history, and ICT would dispell much of the confusion. We may not all live in the information age though, and that seems to be a problem for the oil doomers.

[O]ne can not seriously believe that the world economy is infinitely elastic with regards to energy. With regard to the agricultural system, there is data which shows the limits to this inelasticity and these limits are due to the laws of physics.

More energy is needed to continue world development and accomodate expected population increases. That is not disputed. If and when fossil fuels become scarce and dear we will have to use other methods of energy generation. We will likely continue to improve our industry, and so use less energy for some applications, but that's just good business rather than a mechanism to evade the need for new energy sources.

I will focus on the dollars spent for fuel, chemical sprays and fertilizer. These three items are directly related to petroleum, and using the cost of the day and the price of oil of the day, one can convert these numbers into barrels of oil spent.

This is a silly exercise. None of the fuel or chemicals depend on oil. Fossil fuels are merely a convenient current source of the energy and some of the chemical feedstocks needed. It would be far more meaningful to convert the USDA numbers to an energy measure, kilo-joules or something. But all this would show is that producing food in the US with a low single digit percentage of the population employed in the activity takes a lot of energy.

Experiments tell us that lack of fertilizer will reduce crop yields and that is exactly what oil prices cause--reduction in fertilizer. Why the difference? Precision application of fertilizer rather than the spray-it-all-over-the-place techniques have begun to come into play, minimizing the effect of lessened fertilizer application--so far. Eventually, even that might not be enough to avoid a drop in crop yield.

As with any agronomic practice, cost/benefit decisions are made. If fertilizer is cheap but land, water, labor, debt service and all the other costs are high - then fertilizer will be used with more abandon. As its costs rise this will become a larger factor in the analysis. More importantly, we not only have ways to reduce use through precision application, we have ways to get more of the fertilizer into the plants rather than allowing it to be consumed by soil bacteria or leached away. We have ways to improve overall soil chemistry by balancing nutrients and improving the elctro-chemical potential of soil to get more benefit from less total nutrients.

Agronomic practice is very information intensive. As the relative costs of inputs and capital change over time practices will evolve. Much of this is academic at this time - things we know how to do but that don't make economic sense when energy is cheap - but that may not be so in future. In any event, we know what to do when that time comes, and have reason to expect that this will also provide incentives for even more sophisticated practices to be developed. A ready example of this is the development of crop varieties that are more efficient.

[H]aving shown the problem of planting without machinery, we can see that any reduction of oil is likely to cause a serious drop in crop yield, leading to famine.

No, that has not been shown. Fossil oil is not necessary for machinery or agricultural chemicals. Famine is merely a nebulous yearning for those who get excited about possible disaster. This is an emotional defect that afflicts many people, though most are satisfied with scary movies and feel no need to develop crack-pot social theories.

It can't happen in the U. S., right? Wrong. There was a recent report in the Wall Street Journal talking about how Texas will begin to experience the electricity problems that California is now experiencing. Why? Because we won't build coal-fired electrical plants. For the farmers in the drier parts of Texas, pumped irrigation is the only way they can grow the food we eat. Thus, the effects of peak oil will spread even to our ability to obtain water for irrigation.

So, coal is the only way to generate energy? What about wind mills, solar panels and nuclear reactors? One of the interesting uses for wind energy in Sweden is to pump water. Since wind is intermittent, and tends to be most available when people least need it, they pump water up into reservoirs where it can later be used to generate electricity again. This has multiple conversion losses but it clearly demonstrates the fact that coal is not needed to pump water. Wind-electric pumps are somewhat common in remote areas. The wind is used to generate electricity which powers a submerged pump. It runs when the wind blows, which is adequate for most agronomic purposes, though storage could be added to even it out.

“Today, the extrasomatic energy used by people around the world is equal to the work of some 280 billion men. It is as if every man, woman, and child in the world had 50 slaves. In a technological society such as the United States, every person has more than 200 such "ghost slaves."

I also told him that the energy in one gallon of gasoline represents the physical labor of one human for 3 weeks. After hearing this, my friend then asked me if the modern world doesn't have slavery because of cheap energy. I must admit that was something I wish I had thought of. Slavery still exists in the world, but it exists in the poorer parts of the world. Looking at the calculation about planting corn above, one can understand the need for cheap labor, whether that labor is one's children or property. I must make it clear that I think this is absolutely horrible, but every society in the past was a slave-holding society. If we lose our energy and have to live the life they lived, are we naive enough to think our descendants will avoid the mistakes they made?

Well, no. Technology is not like slavery, quite the opposite. As a US citizen I'd use my 200 slaves to do knowledge work and get very much more value for their time and labor. I'd have them be computer programmers, school teachers, professors and lab rats of all sorts - except the pretty ones who would be prostitutes. In general, I'd provide them the information and energy they needed to be productive, just like me, except that I'd own them and their production. Slavery is not like technology. It is something else entirely. (And not something I'm advocating.)

Peak oil represents a grave threat to our food supply, in my opinion. Few are aware of how important the petroleum industry is to the agricultural revolution in which we live. This is why I am currently trying to buy a farm. Consider this, prior to the agricultural revolution, estimates of hunter-gatherer population sizes, based upon anthropological data show that humans were quite few in number. . .

Agriculture based only upon animal energy allowed the human population to grow to about 750 million by 1750 (Cavali-Sforza, 1994, p. 68). Peak oil will do several bad things to the world's energy supply. It will force us to use coal, and if one uses coal to replace oil, because coal will be used at a faster rate, the US turns its 200 year supply of coal into a 44 year supply (assuming that there really is a 200 year supply to start with). This implies that by the end of this century, we will no longer have fossil fuels with which we can foster global warming. Nor will we have fossil fuels with which to run our tractors and we will return at the very least to the 1750s. Going back to an animal-energy based economy means that approximately 5/6ths of us must die. The post fossil fuel world, lacking some new energy source, will consist of not many more than 750 million souls. What an ugly century this will be. While there are some long-shot grasps-at-straws possible replacements for fossil fuels, the political turmoil resulting from mass starvation may preclude their development and implementation.

Oh dear! Are there really still people who know so little and fear so much that they think they can survive by buying a farm? This is beyond confused, it is affected ignorance in service of some deep emotional problems and intellectual bankruptcy.

Here's a clue. Don't buy a farm unless you are an especially clear headed realist with adequate capital and boundless optimism tempered by humility . . . or so wealthy that it's just a hobby. Take your lessons from old timers like Jethro Tull or even Thomas Jefferson who tried their inadequate best to learn the technologies of agriculture, most of which are biological but that necessarily subsume a great deal of chemistry and physics as well. At the nano scale it all blurs a bit. Oh, and pay attention in business school. You'll need it.