Biologically Driven Water Management

Managing soil in preference of biology affects how much water stays in our fields

The USDA Natural Resources Conservation Service defines soil health as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans.” Human health is generally defined as “the proper functioning of the body and mind.” The word “function” is often defined as “the natural or intended action of something.”

I often ask farmers and gardeners what functions they expect the soil in their fields or gardens to perform. This question is often met with puzzled looks, which tell me that most people who deal with the soil have not thought about what the soil should be able to do in order for them to grow the crops they desire.

We humans are prone to manipulate things, including the soil, to get what we want out of them. In our pursuit to amend the soil we don’t often stop to consider how the soil was designed to function. The point I am trying to make is that we need to pause in what we are doing as farmers and gardeners to understand how the soil is designed to function and how those functions are supported, or undermined, by how we manage the soil.

It's Time to Stop Just Treating the Symptoms

Jon Stika is doing some field soil testing in Vermont.

A recent survey by Farm Progress magazine asked, “Which innovation do you believe will have the most impact on the future of farming?” The results were, “35% — drought-resistant and high-yield crops; 32% — sustainable and regenerative farming practices; 21% — precision agriculture and data analytics; and 12% — automation and robotics.” A second survey asked, “What is the most important factor influencing your crop yield?” The results were, “47% — weather conditions and climate changes; 28% — soil health and nutrient management; 15% — seed quality and genetics; and 9% — pest and disease control strategies.”

These results show how important the topic of regenerating soil health has become to producers across the country. They suggest that producers now recognize that it is time to solve the problem of dysfunctional soil rather than treating all of the symptoms.

As producers of crops, we expect the soil to keep our plants watered and fed until harvest. In order to supply water to the plants, the soil must be able to infiltrate water by letting water enter the soil at the surface. For water to be able to infiltrate the soil, there must be stable soil aggregates — those little lumps, clumps and crumbs held together by biologically produced glues sitting at or near the soil surface. These stable soil aggregates also maintain all the little spaces where the organisms that produce the glues live.

To restore and maintain the soil, we must approach it for what it actually is: a biological system. Like any living thing, the organisms that run this biological system need food, water and shelter to survive and thrive. For most of the organisms in the soil, the preferred source of food is the sugars exuded by living plant roots. If sugary root exudates are not available, soil organisms will consume dead plant material and any organic matter that currently exists in the soil.

Four Basic Principles

If we are to restore and maintain the proper functioning capacity of our soil, we must treat it as a biologically driven system. It is to this end that I have espoused four basic principles of soil health: disturb the soil as little as possible, include the greatest diversity of plants grown in the soil, maintain living roots in the soil as much of the time as possible, and keep the soil covered at all times. These four principles have a goal of supporting the microbiology of the soil and, thus, the soil aggregates that serve as their home and help the soil function in a way that benefits our production of crops.

Now consider these four principles in the context of how you manage the soil in your fields or garden. First, there is no tillage operation that benefits the soil. Tillage can incorporate plant residues, fertilizer or herbicides; it can fill in ruts and prepare a seedbed for planting equipment that is not designed to plant into undisturbed soil. Tillage does not directly benefit the soil; it can only degrade it. This is why it is vital to carefully consider any tillage operation you may conduct in your fields or garden.

Any tillage must be mitigated by emphasizing the other three principles to restore what was lost … to a point. Repeated disturbance and destruction of soil aggregates by tillage will result in a continued decline in soil health, no matter how much you may apply the other three principles of restoring soil health.

Sadly, this is the case on the majority of agricultural land in the U.S., where soils have been degraded in the past and continue to be degraded at present. Degraded and dysfunctional soils require increasingly more inputs of water, fertilizer and pesticides to be productive. Continuing to farm in this manner is neither economically nor environmentally sustainable.

Water Management and Soil Health

With a basic understanding of how soil is supposed to function, let’s take a look at how our management of the soil affects water.

Water is essential regardless of what crop we are trying to produce. Each growing season we always hope to be in the Goldilocks zone when it comes to water: not too much but not too little. Well-aggregated, healthy soil is the great equalizer, regardless of what the weather might dish out each year.

Healthy soil infiltrates water where the two meet: at the soil surface. When water moves freely into the soil, it is then available for plant roots to access as needed. When water moves freely into the soil, it does not pond on the surface but can move into and through the soil to recharge the water table, or it can exit through a tile drainage system that allows any excess water to escape. Whether you are growing crops on dryland, irrigated land, or land that is prone to excess water, healthy soil that allows water to infiltrate is important for profitable production.

Growers will often speak of “opening up” the soil with tillage to increase water infiltration. The reality of using tillage to “open up” the soil is that it also introduces an excessive amount of oxygen into the soil, allowing copiotrophic bacteria to reproduce at very high rates and to literally eat the organic glues that hold soil aggregates together. The result is soil aggregates that do not hold together when they get wet by the next rain or application of irrigation water. When soil aggregates get wet and collapse, the resulting sand, silt and clay particles clog up any pores at the soil surface and seal it off from further water infiltration. Once the soil dries, we see evidence of this in the form of a soil crust on the surface. Often more tillage will be performed to break this crust and “open” the soil back up, causing more soil degradation and poorer water infiltration than before.

Copiotrophic bacteria: from copio- (much — as in “copious”) and -troph (feeding). Copiotrophic bacteria are organisms that thrive in an environment rich in organic matter. The opposite are oligotrophic bacteria ( oligo- as in “few” — like “oligarchy” — rule by the few) — organisms that thrive in low-nutrient environments.

Once you significantly reduce or eliminate tillage, in concert with the other principles of building soil health, the soil’s capacity to infiltrate water will increase dramatically. My own healthy silty clay loam — “heavy” garden soil — will infiltrate several inches of water per hour — a rate that can handle the most severe rain event we might experience here in North Dakota. When we are experiencing a drought, I know that every drop of rainfall or irrigation water will move into the soil where it can be stored for my plants to used as needed.

Reducing Tile Drainage

It is known that excess water leaving a field through tile drainage systems can carry excess nutrients such as phosphorous or nitrogen that can cause significant water-quality issues downstream. Restoring soil health can also play a major role in crop nutrient management.

Here in North Dakota, a soil that has been planted without tillage for at least five consecutive years is estimated to supply about 110 pounds of nitrogen per acre per year, simply from the biology that live in the soil. At the current price of spring wheat and nitrogen fertilizer, such a scenario would call for an additional 50 pounds of actual nitrogen per acre. If a spring wheat crop followed a soybean crop, the recommendation would call for little or no added nitrogen fertilizer. Note that a diverse crop rotation is one of the four principles of soil health.

By implementing all four principles of soil health, some farmers have reduced the use of commercial nitrogen fertilizer to nearly zero. Many producers have reduced nitrogen fertilizer use by half after implementing a system that restores soil health.

Another approach that has been proposed to reduce nitrate nitrogen in tile drainage water is to install a bioreactor filled with wood chips that allows denitrifying bacteria to convert nitrate nitrogen into nitrogen gas that then returns to the atmosphere. Such systems might cost up to $200 per acre to install, and the wood chips typically need to be replaced every ten years. Compare this to a new no-till drill, which might cost $2,800 per foot and be used as part of an overall management system to improve soil health and solve the problem of nitrates in tile drainage water — instead of continuing to treat the symptom of poor nutrient cycling.

Treat Soil as a Biological System

The greatest hurdle to restoring soil health and significantly reducing or eliminating any symptoms related to water management is acknowledging that soil is a biological system rather than regarding it as “dirt.” Once soil begins to function as intended, symptoms of ponding water, erosion, drought, lack of available plant nutrients, etc. become less, and savings from reduced inputs become greater, while addressing any potential environmental issues to boot.

There is no system of crop production more efficient and environmentally friendly than one that mimics nature by restoring the capacity of soil to function.

For reference:

North Dakota Crop Nitrogen Recommendation Calculators: https://www.ndsu.edu/pubweb/soils/FourCropsNitrogenCalculatorWebApp/#

Jon Stika is a conservationist, agronomist and soil health instructor. He served with the NRCS until his retirement in 2015, and he is the author of A Soil Owner’s Manual: How to Restore and Maintain Soil Health , available at bookstore.acresusa.com .