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What Is “Healthy Soil”?

If you are curious about the relationship between agriculture and the environment, chances are good you’ve heard that a healthy food system starts with healthy soil.  But what is healthy soil, and why does it matter? 

First of all, soil is a living ecosystem whose health directly affects the health of the plants that rely on it, as well as the bacteria, fungi, protozoa and other organisms that call it home. Of course, healthy soil leads to healthy plants. But healthy soils also store carbon, withstand erosion caused by extreme weather, and improve water quality, making healthy soils one of the most important tools for reducing carbon emissions and preparing for the impacts of climate change.

According to the USDA’s Sustainable Agriculture and Research Program, there are 7 things that make soil healthy:

1. Healthy Soil Needs to Have Adequate Nutrients

Healthy soils have enough nutrients to feed plants throughout the growing season. They also aren’t too acidic. Having enough nutrients is also referred to as “fertility”. Every soil has some level of nutrients, but generally the more organic matter in the soil, the more nutrients it has. Nutrients can be provided by fertilizers, but high levels of chemical fertilizer risk being washed off by rainfall, leading to water pollution. More sustainable methods of adding nutrients to soil focus on adding diverse types of organic matter like cover crops, compost, or crop rotations. These methods have the added benefit of saving money on off-farm inputs.

2. The Soil Needs Strong, Stable Structure

In addition to plentiful nutrients, a healthy soil has a strong, stable structure. Picture an underground sponge, with pockets to hold water and nutrients, and loosely packed to allow plant roots to develop. This spongy texture also allows rainwater to get into the soil and be stored there, where the water can dissolve minerals in the soil for the plants to take up. Growing different plants with different root systems can build structured soils, as can having high levels of organic matter, which allow the soil to “aggregate” or stick together into clumps, leaving pockets of air and water. In order to preserve strong soil structures, farmers can minimize tillage (disturbing the soil by digging or overturning) and prevent compaction, which is caused by heavy farm equipment pushing down on the soil, pressing the soil together and squeezing out the air bubbles. 

3. Healthy Soil Needs to be Deep Enough

If you’ve ever grown a plant in a tiny pot, you know that plants need space to grow to their full potential. Healthy soils are deep enough to allow the plants’ roots to develop without hitting bedrock below (something that’s easier to fix in a garden box than on a farm). Other bottom layers that can prevent root growth include compacted soil. Sometimes, heavily plowed soil may have a loose, workable top layer of soil, but the layer below may become compact and hard due to the weight of heavy farm equipment (like a soft but thin mattress on the hard floor).

Deep, well-structured soil full of nutrients and beneficial soil organisms has a host of positives for the plants growing in it, as well as the environment. Photo: Frith Farm.

4. The Soil Needs to Have Good Drainage

Healthy soil needs good drainage, not least so that a farmer can work it soon after rains in the spring or throughout the season. Wet soil is prone to being compacted by farm equipment, similar to the way that wet beach sand is much easier to use to build sandcastles! The roots of plants also need air, and the factors that lead to good drainage also lead to “breathable” soil, which allows the roots the oxygen that they need.

5. Healthy Soil Needs to Have Lots of Good Soil Organisms, and Few Bad Ones

Although this criteria seems self explanatory, the presence of beneficial microorganisms can help create a good growing environment for plants. Soil organisms are able to “cycle” organic matter, which means they change organic matter into nutrients that other organisms, like plants, can consume. Plants are able to “cycle” nutrients through photosynthesis, as well as by absorbing nutrients from water in the soil. Soil organisms, meanwhile, do this by eating things that we can’t, like plant roots and manure, and in turn making these nutrients available to plants. The presence of many beneficial microorganisms creates a competitive living environment for harmful pests, and creates healthy plants that can better fend off disease.

6. The Soil Needs to be Toxin-Free

Healthy soils are also free of toxins that could harm the plant, either natural or introduced by humans. Unfortunately, harmful toxins can be introduced by things like toxic sludge or oil spills. However, bacteria and fungi are able to process and remove these chemicals, which is another reason that microorganisms are key to healthy soils.

7. Healthy Soil Needs to be Resilient

Best of all, healthy soils are resilient. That means that they resist being degraded, and when they do encounter adverse conditions, they are quick to recover. This resiliency is powered by all the other elements of healthy soils: when there is a lot of organic matter in the soil, soil particles cling tightly together and resist erosion. When healthy microorganisms are present, they are able to detoxify the soil in the event of contamination. These qualities and more are why healthy soils will be an important part of our agricultural system in the face of a changing climate.

There are proven strategies to improve soil health, but every farm uses different techniques according to the opportunities and challenges that farm has. Soil health is important for successful farm businesses, but healthy soils are also crucial in fighting climate change and creating resilient food systems. In recent decades, farming practices like intensive tillage and use of chemical fertilizers have led not only to soil loss through erosion and run-off, but also greater carbon emissions and reduced carbon sequestration. Luckily, there is a lot of great work supporting healthy soils in Maine, including the formation of the Maine Soil Health Network and the recent passage of the Maine Healthy Soils Program. In future blog posts, we will dive further into why soil health matters, how healthy soils help make farms resilient to climate change, and visit some Maine farms on the leading edge of cultivating soil health.

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