Crop Diversity Pays Off

Conventional agriculture production systems in developed countries rely heavily on fossil energy, but emerging uncertainties in energy supply indicate a need to better understand energy efficiency in conventional and alternative systems.

So begins a press release from the American Society of Agronomy to highlight a recently published paper titled “Fossil Energy Use in Conventional and Low-External-Input Cropping Systems.”

It is difficult to design long-lived field experiments in agriculture that ask questions about effects of crop diversity on crucial parameters such as energy and fertilizer use, weed control, yields and profitability.  But this is what a group of scientists at Iowa State has done.  They have a produced numerous publications and posters explaining the work, but the recent subject of the press release is still behind a pay wall. Why are they doing this?  One of their posters explains:
Conventional cropping systems in the central U.S. have low levels of biological diversity and rely heavily on synthetic fertilizers and herbicides, which commonly contaminate water in this region. Ecological theory suggests that diversified cropping systems integrated with livestock should foster reduced reliance on agrichemicals and fossil fuels, and should lower production costs and pollution.
Of course my interest perks anytime somebody connects ecological theory to agronomy.

Ecological Theory:  Good to Know, Best to Apply

I’ll repost a few graphics from the posters to summarize the results, but first a bit of explanation on their design.  The typical crop rotation pattern in their geography is a two year corn/soybean pattern (in many case corn actually just follows corn).  These are summer crops, which leaves fields bare over the winter.  They tested two alternative rotations:  a 3 year rotation of corn/soybean/small grain that also includes red clover as a winter cover crop and green manure, and a 4 year rotation that adds alfalfa to the pattern.

An overhead view of the study plots, each of which is 18 m by 85 m.

Energy use was dramatically less due to reductions in fertilizer and herbicide applications.

Even with dramatically lower inputs, yields were actually slightly higher for the 3 and 4 year rotations.

Lower inputs with greater yields means the energy gain is much higher with the longer rotations.

The lower input costs compensate for an increase in management costs, making the financial returns similar among rotations.

Keep in mind that these returns were at commodity prices, not the sort of premiums that come from selling organic, local, or on a fair trade contract basis.  Given these results, and generally rising costs of inputs over time, I expect conventional farmers will begin adopting organic type practices, whether or not they are completely free of synthetic pesticides and fertilizers.  The name used by the Iowa researchers for this kind of farming is Low External Input (LEI).  No matter what your preferred label, reducing external inputs and developing agricultural systems that produce their own fertility as much as possible is certainly a worthy goal.