Diversification: Nature Knows Best

A study  in Science (see article in Renewable Energy Access) from David Tilman, an ecologist at the University of Minnesota shows what we should have known all along:  When energy crops are grown sustainably in poor soil (i.e. most of our available land) without fertiliser, a diverse mix of native prairie plants yeilds more than twice (238%) as much harvestable energy than any monoculture (including the much-hyped switchgrass) grown on the same land.

At some point, humans are going to have to realize that our production-line mentality, which seems so efficient to us, is not really the best way to do things.  We like farming just one species in neat rows because it’s easier for us to comprehend.  But easier to comprehend is not the same as more effective.  In money management, we know that there is no one perfect security for an investor: diversification allows higher returns with lower risk.  Farmers have yet to (re)learn that lesson: growing just one crop puts strains on the particular resources that crop needs most, and allows specialized pests an environment of limitless growth.

Monocultures are sub-optimal, both in your fields and your portfolio.   Enron employees with their retirement fund in 100% Enron stock learned that the hard way.  As we transition to a new energy economy, I hope that David Tillman, and researchers like him will help us realize that the places we grow out energy crops don’t have to be like an Enron employee’s 401(k).


  1. Preston said

    It seems like I learned in elementary school that crops had to be rotated or the yield would drop. I guess this lesson is forgotten by the professionals?. Nice post.

  2. tomkonrad said

    Not totally forgotten, but when we’re talking about switchgrass and short rotation woody crops such as poplar, we’re talking about perennials that don’t get replanted every year. So the only way to get a mix is to have everything growing at the same time.

    I’m not an expert on modern farming techniques, but I think a lot of modern farmers “make up” for limited crop rotation by adding lots of fertilizer.

  3. Mike said

    Crop rotation between legumes (beans, alfalfa etc.) and monocots (corn, switchgrass, etc.) is a common rotation. Legumes are nitrogen fixing plants which means that they are able to take nitrogen that is unavailable to the plant and convert it to an available source. This process produces an excess of nitrogen that is then available for the next year’s corn crop. Grasses cannot fix their own nitrogen and they are dependent on outside fertilizer supplements, either commercial fertilizer, manure, or green manure, ie legumes.

    A very common misconception is that crop rotation or native species do not need fertilizer. This is patently false. Think of your basic laws of nature. If biomass is removed from a field, then the chemical elements that make up that biomass is also removed. In particular, potassium and phosphorous are critical high volume elements that must be replenished for the field to continue to produce an economic yield. Regardless of what people may claim, there is no way around this fact.

    While I agree that we need to be looking for sustainable methods to produce all of our crops, it is critical that we understand that nothing is free and we will need to maintain soil fertility levels to maintain crop yields.

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