Ecosystems are not smart, we are.

posted in: Science | 8
Cover crop seed blend of 17 species
Cover crop seed blend of 17 species

In my recent post Don’t mimic nature on the farm, improve it, I argued that we should cast aside the ideas of “balance of nature” and “nature knows best” in designing farming systems. There is no reason to “follow nature’s lead” if nature has not been optimized by any process that we know of, and therefore consists of mostly random mixes of species dictated primarily by natural disturbances. But if we don’t, what are we left with?

We are left with an agriculture based on human ingenuity, consisting of:

  • Crop rotations; or better yet, dynamic crop sequences.
  • Residue management and no-till planting to keep the soil covered and control erosion;
  • Careful use of synthetic fertilizers in conjunction with organic fertilizers;
  • Cover crop cocktails (This is where we can study unused and underused species to take advantage of “nature’s wisdom”. Precision crop planting in sequence with cover crops could potentially improve cover cropping benefits by allowing crop roots to advantageously colonize the root channels of the dead cover crops, i.e., sequential root channel colonization.);
  • Genetically modified crops, including cover crops someday;
  • Integrated pest management, including the use of improved pesticides.

All of these practices could be more widely used and more effectively applied.

What about those practices that are promoted because they mimic nature? Denison, in Darwinian Agriculture1, evaluates four of these nature-based practices: perennial grain crops, reliance on only local sources of nutrients, intercropping, and reliance on diversity to control pests. He then goes on to survey the evidence for each and gives his assessment. I’ve summarized Denison’s assessment here:

  • Perennial grain crops – Perennials have their place, especially in feeding livestock, but due to low yields, “given the tradeoff between perenniality and seed production, emphasis on grain production may be misplaced.”
  • Reliance on only local sources of nutrients – With regard to following nature, “local sourcing of nutrients in natural ecosystems is a constraint imposed by lack of external inputs, not an example of ‘nature’s wisdom’.” In other words, although it may be advised to use local sources of nutrients as much as possible, it should not be a constraint to us, just because it is a constraint of natural lands.
  • Intercropping – There are errors commonly found in intercropping experiments, chiefly the failure to find or use the optimum density for the monocropped plots, an error which favors the intercropped plots. The design of these types of experiments is complex, but even in those carefully designed, “most intercrops yield more than the average of the two [or more] crops, but less than the best crop alone.” In this case, farmers will tend to grow the best crop. “Diversity may be there for a reason… but that does not mean that diversity is there for a purpose.”
  • Reliance on diversity to control pests – We can compare diversity in space (the “balance of nature” that inspired intercropping) with diversity in time, or crop rotation (which has a long history of success and is not commonly found in nature). With intercropping, you expend the advantages of diversity (here, for pest control) the first year the intercrop is planted. What do you do for diversity the second year? On the other hand, with crop rotation, the whole system changes each year. The latter may work better than the former in the long run, but no research that has addressed this question. Nevertheless, there is no lasting solution to pests; “ongoing evolution [of pests] will tend to undermine all of our pest control measures, not just those based on toxic chemicals.” We cannot get off the pest control treadmill.

Although I think we would be better off without the “mimic nature” baggage, I am not saying that biodiversity is not important. We should incorporate more diversity in our cropping systems, not because nature is diverse, but so we can better use the properties and processes in individual plants. If it exists anywhere, the “genius” of nature is in individual species and not in the ecosystems. Right now, other than corn, soybeans, rice and wheat, we have not thoroughly explored the capabilities of many plants, domesticated or not.

Neither am I saying that interactions between species are not important. We should study intentional combinations of species, mixtures not found in nature, searching for simple, direct interactions between species that will give us our desired results. As Denison points out, we may gain more knowledge of individual species when they are studied in communities with other species – a job for agroecologists! However, if the idea that the sustainability of natural ecosystems depends on complexity is an illusion, agricultural systems should only be as complex as needed for our purposes, not more so.

Another benefit gained by casting aside “the romantic notions of a stable Eden”2 is that it should make us less susceptible to “silver bullet” solutions, wishful thinking and other such nonsense. In my experience, this is most needed in soil and pest management. There are no quick, easy, and cheap methods to improve soils. It takes bulk organic materials, either grown on-site (less expensive) or imported (more expensive). In the long-term, the nutrients that are harvested in the crop must be replaced; they cannot be produced by “better biology.” For insects, weeds, and disease, no amount of tweaking the system will make them go away.

There are those who will find this whole notion yet another example of arrogant man trying to control nature, and there are plenty of examples of where we have done a poor job at managing the Earth. However, we must realize that farming is controlling nature for our own purposes. We still need nature, and “wild” places, but unless critics can point to a mechanism by which natural ecosystems were consistently improved, we should not use them as blueprints for agriculture, nor should we assume that we cannot improve on them. There is no utopian state of nature, so we can stop trying to restore, recover, or regain any such state in agriculture. There is no way back, but there is a way forward.

1 Denison, R. F. (2012). Darwinian Agriculture: How Understanding Evolution Can Improve Agriculture. Princeton University Press. (Denison’s other main thesis in this book is that natural selection has left us few tradeoff-free opportunities for genetic improvement through genetic engineering. Full Disclosure – Denison served as my major professor in graduate school at UC-Davis. For more from Denison, view his Darwinian Agriculture blog.)

2 Marris, E. (2013). Rambunctious Garden: Saving Nature in a Post-Wild World. Bloomsbury Publishing USA.

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Andrew McGuire is an Irrigated Cropping Systems Agronomist for Washington State University Extension. He works with farmers in the Columbia Basin of Central Washington in improving soils through cover crops and high residue farming systems.