The Dirt on Dirt - Why soil health matters

Published on Fri, 03/31/2017 - 8:00am

Spring is finally upon us! That means we should soon (if not already) be working with soils in our fields, gardens, and landscapes. The foundation to a successful crop production system depends on good soil. Good sound soil management is required to meet essential plant needs for water, nutrients, oxygen, and a medium to hold their roots with as little management as possible.

Terms like “soil health” and “soil quality” are becoming increasingly popular terms when discussing soils

In many cases, the term soil health is used interchangeably with soil quality. In general, soil health, as a measure of soil functions, can be defined as the optimum status of the soil's biological, physical and chemical functions. In simpler words, this means healthy soils can sustain plant and animal productivity, soil biodiversity, maintain or enhance water and air quality, and support human health and wildlife habitat. 

The definition of soil health provided by USDA-NRCS states, “soil health is the continued capacity to function as a vital living ecosystem that sustains plants, animals and humans.”

Larger than a medium

A healthy soil is not just a medium to grow plants, but rather a living, dynamic, and changing environment that is influenced by what we do and the practices we adopt as human activities. Soil is a dynamic and living organism. Some philosophy to soil health suggests we need to apply the human health principles as its metaphor. We, as humans, strive for healthy bodies to perform our tasks most efficiently so the thought our soils should do the same.

Soil health suggests that soil is an ecosystem that needs to be carefully managed to function optimally. Important soil functions would include:

•     Retaining and cycling nutrients

•     Supporting plant growth

•     Allowing infiltration, promote storage and filtration of water

•     Supporting the production of food, feed, fiber, and fuel

•     Suppressing disease, insects, and weeds

•     Sequestering carbon

•     Detoxifying harmful chemicals

When soil does not perform to its potential, the long term end result can jeopardize productivity and environmental quality, thus affecting farmer profits. If we know what constitutes a healthy soil we can then better manage our soils. So let’s look at the different characteristics that make a healthy soil:

Good soil tilth

Soil tilth refers to the overall physical character of the soil and its suitability for crop production. Soil with good tilth is crumbly, well structured, dark with organic matter, and has no large and hard clods. Good tilth goes hand-in-hand with good soil structure. Soil structure refers to the way soil aggregates, particles, and pore spaces are arranged. Soil management practices, like plowing, cultivating, applying lime, adding organic matter, and stimulating biological activity, can influence structure.

Lack of structure can affect plant growth in many ways. Poor structure affects air exchange and water movement, which in turn affects nutrient utilization. Lack of structure influences the quantity and size of pores which can directly impact root growth and development.

Sufficient depth

Sufficient depth refers to the extent of the soil profile through which roots are able to grow to find water and nutrients. A soil with a shallow depth as a result of a compaction layer or past erosion can be more susceptible to damage in extreme weather, thus putting a crop at more risk to flooding, pathogen attack, or drought stress.

Good water storage and good drainage

During a heavy rain, a healthy soil will take in and store more water in medium and small pores, but will also drain water more rapidly from large pores. Thus, a healthy soil will retain more water for plant uptake during dry times, but will also allow air to rapidly move back in after rainfall, so that organisms can continue to thrive.

Sufficient supply, but not excess of nutrients

An adequate and accessible supply of nutrients is necessary for optimal plant growth and for maintaining balanced cycling of nutrients within the system. An excess of nutrients can lead to potential water quality issues, high nutrient runoff, as well as toxicity to plants and microbial communities within the soil profile.

Small population of pathogens and pests

Plant pathogens and pests can cause diseases and damage to the crop. In a healthy soil, the population of these organisms is low or is less active. Healthy plants are better able to defend against a variety of pests.

Large population of beneficial organisms

Soil organisms help with cycling nutrients, decomposing organic matter, maintaining soil structure, biologically suppressing plant pests, etc. A healthy soil will have a large and diverse population of beneficial organisms to carry out these functions and thus help maintain a healthy soil status.

Low weed pressure

Weeds compete with crops for water and nutrients that are essential for plant growth. Weeds can block sunlight, interfere with stand establishment, cultivation and harvest operations, and harbor disease causing pathogens and pests.

Free of potentially harmful chemicals and toxins

Healthy soils are either devoid of excess amounts of harmful chemicals and toxins, or can detoxify (or bind) such chemicals. These processes make these harmful compounds unavailable for plant uptake, due to the soil’s richness in stable organic matter and diverse microbial communities.

Resistance and resilience to degradation

A healthy, well aggregated soil is resilient, full of diverse organisms and is more resistant to degradation from wind and rain erosion, excess rainfall, extreme drought, vehicle compaction, disease outbreak, and other potentially damaging influences.

Poor soil problems

It is important to recognize soil constraints that limit crop productivity, farm sustainability, and environmental quality. Management practices can be adjusted to alleviate these problems. The following is some of the more common soil constraints commonly observed in unhealthy soils:

Soil compaction can occur at the surface and subsurface soil profile. Be sure that a soil is ready for equipment prior to tilling.

Poorly aggregated soils are more susceptible to erosion and runoff which increases risk of lost productivity. Aggregates are formed whenever mineral and organic particles clump together.

Weed Pressure, when plants are unhealthy and “weak” they are less able to compete against weeds for water and nutrients and defend themselves against pests.

High pathogen pressure, root pathogenesis negatively impacts plant growth and root effectiveness as well as minimizes contributions from microbiota in proper functioning of important soil processes.

Low water and nutrient retention, lower organic matter in soils indicates poor structure and lower water holding capacity. Therefore nutrient mobility and plant growth will be limited.

Heavy metal contamination from past human activities, such as high traffic, commercial activity, spills, or pesticide application, can negatively impact soil and plant health.

Dig into expert help

As you work your soils, good sound soil management can begin and the dividends of better crop production can hopefully be seen. Further needs would be to conduct a soil test which your local County Extension Office can assist you with, if needed. Knowing and understanding the health of your soil along with knowing your soil fertility will certainly help in implementing proper soil management techniques.

There are many resources that discuss in length the philosophy of soil health and the management of our soil to create a quality soil that is healthier and more productive. USDA-NRCS has a wealth of soil health information, videos, fact sheets, and more. And for those that want more information, Cornell University offers the Comprehensive Assessment of Soil Health, a manual offering in-depth discussion onsoil health.