Agriculture

Old McDonald versus the Rhizosphere

10,000 years ago, atmospheric CO2 levels were 180ppm and dropping. 110 years ago, the CO2 level was 280ppm and rising. I would love to see CO2 measurements in between. The world in 1900 was relatively unindustrialized compared to 1920 or 1950 or 2000. The fact that the CO2 levels did not inflect upwards with dramatic slope changes ("hockey stick") following the enormous increase in industry after World War 1 tells us something about anthropogenic causes. Agriculture has been modifing CO2 levels for quite a while.

I am learning something about the "rhizosphere", the root system of the world's land plants. CO2 levels in the soil are 10 to 500 times higher than in the air, and much of that CO2 forms carbonic acid. That and other root-generated acids aggressively break down rock, releasing nutrients (like phosphorus) and sequestering CO2 as carbonate rock. Carbonate rock is a major long term carbon sink, storing vastly more carbon than the ocean, which in turn holds far more carbon than the atmosphere.

This makes me wonder about the different root behavior of wild plants versus food crops. Many perennial wild plants reach down to rock, slowly etching out the phosphorus and other minerals, sequestering CO2. Do annual food plants reach down that far? When we supply food plants with fertilizer, does that make their root systems more shallow, not engaging in the deep rock surface processes used by the wild plants preceding them to bring nutrients to the surface and dispose of CO2?

While we must rethink the CO2-releasing mechanical technologies that we've built over the past century, we must also look much deeper into our agricultural past and the planting, tilling, and fertilizing technologies with which we feed ourselves. Modern agriculture rests on a rapidly dwindling supply of rock phosphate, which replaced the exhausted sources of guano fertilizer popularized by Humboldt only 200 years ago.

With hundreds of years worth of coal and gas shale, we can (foolishly?) continue carbon fuel extraction for a long time. But what happens when we run out of cheap phosphorus, especially if we replace wild habitat with "fuel crops" with shallow roots and a huge appetite for fertilizer? If fertilizer gets too expensive, and crop yields plummet, will we eat up even more wild habitat for agriculture? Will "peak food" happen long before peak oil?

• Where can I learn more about the rhizosphere and deep root structures?
• How do wild plants and perennials differ from annuals in the depth of their roots, the weathering and carbonation of deep rock, and the extraction of phosphorus from it?
• What are the consequences of our transformation of the world's plants?

There are a lot of question marks in the above. I hope there are encouraging answers to all of them. But our demonization of mineral and machine sources of CO2, and the messianic pursuit of agricultural "green" fuel sources, may be moving us from a big problem to an insurmountable one. Just because Old McDonald had a farm, and CO2 was lower in his day, does not mean that we can survive the into deep future using his traditional practices.