Until recently, it seemed that cheap oil could override constraints imposed on agriculture by lack of land, soil and water. What is the oil connection? Where is oil (or more generally, fossil fuel) used in agriculture?

We'll use the example of corn production in the US, focusing only on farm production. That is, we'll exclude energy inputs associated with processing the corn into food products. What are the major energy inputs into corn production?

In decreasing order (by kcal/ha; where kcal = kilocalorie [kilogram calories] or quantity of heat equal to 1000 gram calories), the "big 8" in US corn production are:

BI390000.gif nitrogen fertilizers

BI390000.gif irrigation

BI390000.gif gas + diesel fuels

BI390000.gif machinery (including energy costs of manufacture)

BI390000.gif drying of harvested corn

BI390000.gif seeds (includes all inputs required to produce the seeds)

BI390000.gif phosphorus fertilizers

BI390000.gif herbicides

(See papers by Pimentel on energy inputs in US corn production and the National Reseach Council book on agriculture, both on the supplementary reading list, for more information on energy inputs in agriculture. The order of energy inputs given above is from Pimental.)

In fact, as you might expect, fossil fuel energy inputs into agricultural production increased rapidly over most recent decades. Again, using corn in the US as an example (see Pimentel et al. on the supplementary reading list and the update in Pimentel and Dazhong), the energy efficiency of production, calculated as the ratio of corn energy out to energy put into its production (energy out/energy in) changed as follows (ignoring the sun's input of energy, which is the greatest, of course!):

(ratio of corn out/energy in):

Ratio in 1945 = 3.5

Ratio in 1983 = 2.5

Between 1910 and 1983, corn yields in the US increased by 346% (on a per area basis), which the energy inputs increased by 810%, also on a per area basis!

That is, we are putting more and more fossil fuel energy into production for a given level of output! Viewed slightly differently, we're not getting as much more corn out as we are putting extra energy in; the efficiency ratio is worsening over time!

This energy intensiveness has implications for the sustainability of many current agricultural practices, and also for climate change and other issues that we'll discuss later.

I have read that US farmers decreased their energy use by close to 41% during the 1980's and 1990's as fuel prices rose steeply, through a combination of methods (changed methods of irrigation, applying fertilizers and pesticides; overall reductions in fertilizer use; using compact fluorescent bulbs in animal confinement facilities, and so on) [Leopold Letter spring '05]. If this is correct, it is great news!

The same newsletter, however, indicated that rising energy costs are likely to make business as usual impossible for US farmers. That source reported that rising energy prices in the year 2000 cost US farmers about $3 billion in lost income. As prices for fossil fuel-based energy continue to increase, use of alternative sources of energy will become more and more attractive, both economically and ecologically.

The next section (">>" at the bottom of this page) discusses the fertilizer aspects of this equation. ("Navigate" )