Kevin Eicher

At the first Annual meeting of the Nishnabotna Water Defenders, our guest speaker, Liz Garst was asked why she had not mentioned the importance of planting and preserving trees while talking about improving soil erosion and water quality.

Her response was, and this is not a quote, that she thought herbaceous plants were more important. She did not have time to explain why she thought that. I have not spoken with her about this, and I am not putting words in her mouth, but I would like to offer a perspective that might shed some light on the subject.

It’s not that trees are bad, or even not good enough, the subject was about erosion and water quality, and I have to agree that “herbaceous” plants are hard to beat when it comes to reducing erosion and improving water quality. Here’s why I say that:

A healthy, diverse pasture that contains grasses, forbs and legumes will have healthy roots that can grow to astonishing depths. Those plants will put anywhere from 25-75% of their energy back into their roots. For root growth yes, but mainly as sugars that feed the microbes around those roots. They can be so specific about what kinds of microbes they feed, they can feed exactly the microbes that can deliver the nutrients they need for whatever stage of growth they are in.

In the prairies that were plowed under in the Nishnabotna watershed 150 years ago, however tall the grass was, 60-80% of the plant matter was below ground. For a truly fascinating read, look up Dr James White’s work on the rhizophagy cycle at Rutgers University, showing that plants ingest bacteria, strip them of their nutrients and spit them back into the soil, programed to consume exactly the nutrients the plant needs next.

But I digress. As the microbes around those roots eat and are eaten, they begin to form a product that is loosely called “soil organic matter” and a long-term form of carbon called “humus” that create soil aggregates (structure) and stores carbon that can last from decades to centuries, deep down into the soil.

Now let’s talk about water, our favorite subject. As you grow soil organic matter, your soil develops structure that holds together in water. We all saw that in the demonstration Liz showed us on Sunday. It also allows oxygen down into the soil enhancing the growth of “aerobic” microbes that are healthy for plants as opposed to anaerobic microbes that tend to be unhealthy for plants.

Those same spaces between soil particles also allow water to penetrate and be held in the soil. That water can eventually sink to bedrock and form aquifers that feed springs, that feed streams and rivers.

Here’s where I believe it becomes important to why Liz wants to steer the conversation to no-till and cover crops:

The average soil in Iowa today has between 2-4% organic matter. It is estimated that Iowa soils once averaged between 5-8% and sometimes more.

As a rule of thumb, again it varies according to soil types etc., for every one percent increase of soil organic matter, facilitated by not tilling or plowing and making sure there is a living root in the soil year-round if possible, your soils water holding capacity can increase between 20-27,000 gallons of water in the top six inches per acre.

That is huge. This reduces the runoff that carries all the pollutants into our river and it holds water where plants need it, and it feeds the aquifers below. As an added bonus, that amounts to about 11,600 pounds of carbon stored in the top six inches of each acre as well. To see an example of all this in action, watch the documentary, The Biggest Little Farm. That was the beginning of my journey to soil health and regenerative agriculture.

But there’s more. Australian soil microbiologist Walter Jehne has argued that the health of soils and vegetation in the top six inches plays a central role in regulating the water cycle and, through it, the climate. He calls topsoil the “sponge” that covers most of the healthy regions of the earth that have topsoil. This sponge and the plants along with the soil organic matter within it, facilitate “evapotranspiration”.

Evapotranspiration, (I just wanted to say it again) is how vegetation influences climate by moving water from the soil to the atmosphere and cools the land. Land degradation and bare soil changes rainfall patterns. Restoring soil health globally could significantly regulate climate and help reverse global warming by restoring the water cycle.

Now, back to those trees: Of course the trees are important. They stabilize the banks of waterways, they evapotranspire tons of water into the atmosphere and the store tons of carbon deep in the soil. The practice of silvo-pasture, the combination of trees and pasture is a well established way of creating very productive land, especially if the trees put on some form of fruits or nuts that can be harvested or fed to livestock.

For now, at least for now, we need to show farmers how to produce what they know and that is corn and beans, while growing soil organic matter and increasing water holding capacity at the same time.