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1808 PD: The View from Here: A simple model

Mike Gangwer Published on 09 December 2008

The orderly progression of plant growth is manifest organically.

As I write this, rain is falling. But when the storm passes the warmth of the sun dries a crop, and then harvest is begun again.



This is harvest season in the Midwest. The soybeans have nearly been harvested; the corn grain is still standing in most fields. For dairy farms, all the corn silage and the final third or fourth cutting of alfalfa is harvested. Cover crops have been planted and the new green shoots are clearly evident in the silage fields.

Agricultural scientists, like me, enjoy the orderly progression of the organic world. Certainly we know that the seasonal variation is due to the elliptic orbit of our planet around the sun and the tilt of our rotational axis. We know that crop growth is a function of four requirements:

1. Sunlight
The solar radiation that is the result of solar fission: four hydrogen atoms fuse together with one atom of helium formed; energy is released traveling 93 million miles to planet earth (about nine minutes elapses).

2. Water
For those of us particularly interested in soil physics, we study water flow through the soil-plant-atmospheric continuum (SPAC). As an example a corn silage plant, as a C4 cultivar, requires at least 700 pounds of water to go through it, while growing, for every pound of plant dry matter. The alfalfa plant, as a C3 legume, requires double that much water over the growing season. Thus, in terms of global rainfall, for those locations that are rain-fed instead of irrigation-fed, crop production can occur because rain falls during the growing season (in most years, anyway).

3. Soil
Soil must be fertile. We know, for instance, that the soil must contain about 13 or 14 essential elements for crop growth. Three essential elements are found in the air (carbon from carbon dioxide) and water (hydrogen and oxygen). But those in soils, like nitrogen, phosphorus, potassium, calcium, magnesium to name a few, must be part of the soil matrix. These must be adsorbed to soil particles, namely clayey particles.


They are found here from the mineralization of organic matter or the addition of nutrient sources like fertilizers, manures and organic byproducts. All farmers know this too: these nutrients must be put into solution so they can be desorbed from the soil particle and enter the plant root via a process we call transpiration. This term describes the physical and mechanical process of water flowing against gravity. That is, water flowing from a high potential to a low potential (all water runs downhill, or in this case, all water moves from a wetter soil to a drier air). If that water evaporation moves through a plant xylem (straw-like apparatus) as transpiration, then it will carry with it the nutrient solutes that are the building blocks of plant growth.

4. Seeds
The fourth requirement is genetic. That is, farmers must have seed. Plant seeds are the genetic material that once exposed to water, a few enzymes and hormones, and an energy source including inside the seed (germplast) and outside the seed (the warmth of soil in spring). Genetic robustness is carefully explored in plant breeding research laboratories the world over. And yet there are those seed repositories scattered around the world that harvest, store and stabilize the seeds that are what many consider to be old seed germ that cannot be lost.

I recall a visit two years ago in Syria at the International Center for Agricultural Research in the Dry Areas (ICARDA). Here, located in a bunker in the soil, was a huge repository of “ancient” seeds from what is known as the Fertile Crest (the birthplace of cereal grain production 10-12,000 years ago).

If done correctly, these four ingredients yield the tremendous quantities of crop material for human and animal consumption, and for the plethora of products that we use in our lives every day.

As I have written in this column many times, the simplicity of this model: sunshine, water, soil and seed, has been a part of our human existence for many centuries. Farming is manifest in simple terms. I often state that growing up on a farm was my greatest educational experience; my college degrees, including my doctorate, are mere refinements of what I learned on that dairy farm in Parkdale, Oregon.

Certainly, we cannot take this model for granted. If soils are devoid of organic matter and nutrient-starved, all the sunshine and water and seed will not yield much crop growth. If we do not have the heat units to drive photosynthesis, the oxidation of water, and the transpiration of soil nutrients into the shoot and leaves of a plant, then we will not have much crop growth.


For many global agricultural scientists, water, both quantity and quality will be the limiting requirement. In much of the world, societies are already realizing that current practices are unsustainable. Case in point is India, parts of China, and yes, the western side of the United States.

Two fundamental conclusions can be drawn from this simple agricultural model. One, we ought not ever take our production agriculture system for granted. I was recently asked by my supervisor to give the one resource concern that I thought was most neglected here in Michigan. I reported “land use.” The removal of crop fields with Class I and II soils here in the rain-fed system, for non-farm development in some form, would someday be recognized as short-sided. This concern is widespread across the entire landscape unless there are stringent land use laws.

And two, we must think strategically. In the global model, identifying those locations on planet Earth that have the first three requirements nearly all of the time (sunshine, water, soil fertility) is important, but what is more important is protecting them for many generations after we are gone. This is not easy work. Balancing tactical needs with strategic goals requires sacrifice right now. Yet our policy makers can easily defer to the next generation of decision makers.

But for now, when the rains finally stop here in the Midwest, the corn grain harvest will continue. Grain driers will work around the clock. And then snow will fall on fields once more.

Every time I visit the field, regardless where on the planet it may be, I am struck with the elegance of seasons and plant growth. Or written this way, something in me is made more peaceful knowing that we can have a harvest time. The organic model worked one more time. This is manifest organically.

As we enter the fields again, let us know that we are mere participants; we do not have and we never will have absolute dominion over this process. Perhaps better stated, walking in a crop field at harvest is quite humbling indeed. I know less and less every time I am here. PD

Mike Gangwer
Nutrient Management Specialist