Soil Health, Drainage, and Improving Soil

Key points about soil health, drainage, and improving soil 

• Soil health is the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans (USDA-NRCS).
• Most soils have been altered from their natural state. Urban and suburban soils, in particular, have been degraded: topsoil removed, compacted, and depleted of organic matter.
• Test your soil to get information on soil pH and nutrient and organic matter levels.
• Improve soil health by adding organic matter, keeping the soil covered with a diversity of plants, and disturbing the soil as little as possible.

The soil health concept

“Only 'living' things can have health, so viewing soil as a living ecosystem reflects a fundamental shift in the way we care for our nation's soils. Soil isn’t an inert growing medium, but rather is teeming with billions of bacteria, fungi, and other microbes that are the foundation of an elegant symbiotic ecosystem. Soil is an ecosystem that can be managed to provide nutrients for plant growth, absorb and hold rainwater for use during dryer periods, filter and buffer potential pollutants from leaving our fields, ... and provide habitat for soil microbes to flourish and diversify to keep the ecosystem running smoothly.” (Source: Healthy Soil for Life - USDA Natural Resources Conservation Service Soils) 

To improve soil health it helps to understand that the chemical, physical, and biological qualities of soil are interdependent.

Example: When soil becomes compacted it is physically changed (less space between soil particles). This reduces root growth and the uptake of plant nutrients (chemicals), and reduces biological activity, as soil organisms will have less oxygen and less room to move and reproduce.

Indicators of healthy soil

• Plants are thriving.
• Soil is loose and deep enough to allow for good root growth.
• Topsoil is medium to dark brown in color.
• Earthworms, beetles, ants, and other soil animals can easily be seen in the top six inches of soil.
• Soil is crumbly when moist. Soil aggregates (small clumps or crumbs) maintain their shape after a heavy rain.
• You can dig a hole 2-3 ft. deep without too much difficulty.
• Water does not stand on top of the ground hours after a rainfall and soil particles do not move off-site during heavy rainfall.

Soil testing can you help you learn more about a soil’s chemical and biological qualities

• Soil pH is a measure of soil acidity. Most garden and landscape plants grow best in the 6.0 - 7.0 range. Ericaceous plants like blueberry and rhododendron grow best in acidic soil with soil pH of 4.5 - 5.2. 
• The levels of important nutrients, such as phosphorus, potassium, calcium, and magnesium, are measured and reported.
• A test for soil organic matter is usually included in basic soil tests. A level >2% is desirable.
• Many soil testing labs can also test for heavy metals like lead (Pb).

How to test soil drainage before planting

Quick soil drainage (percolation) test

• Dig a hole 12 inches deep and 12 inches in diameter.
• Fill it with water. The next day, fill the hole with water again.
• All of the water should drain out within eight hours.
• If the water drains out more than four inches per hour, the soil is extremely sandy. Less than 1 inch per hour is too slow and may indicate soil compaction, a high clay content, buried debris, a high water table, or a restrictive layer of soil. For help with poorly drained soil go to our Common Soil Problems page and scroll down to "Heavy Soil (clayey) / Compaction / Poor Drainage."
• (PDF) DIY Soil Drainage Perk Test - UT/Knoxville

Improving clay soil and using gypsum to improve soils

• Most Maryland soils are made up of mineral particles- sand, silt, and clay (about 45%); organic matter (about 1-5%); and air and water- pore spaces (about 50%). Soils are classified largely by their texture and that is determined by the relative amounts of sand, silt, and clay.
• Clay gets a bad rap, but it is an important constituent of soil because it holds nutrients and water. But too much clay can cause problems.
• Soils high in clay (more than 50%) feel sticky, don’t drain well, and become rock hard when dry. You can’t change the texture of your soil (the percentage of clay) but you can improve soil structure (the arrangement of individual soil particles).
• Adding lots of organic matter such as compost, farm manure, or shredded leaves to clayey soil will allow it to drain more easily and hold the right amounts of water and air for better plant growth and increased biological activity. Adding sand can be tricky and typically is not recommended to be added to clay soil. 
• Gypsum is calcium sulfate and is often recommended as a 'clay buster'. Despite what the bag proclaims, there is no scientific evidence that it can improve the structure of Maryland soils. It is a good source of soluble sulfur and calcium and can be useful to add to soils that are low in these two nutrients and are in the correct pH range (6.0-7.0 for most garden and landscape plants)

Managing soils for good health

There are four key practices for improving soil health that fall under two broad categories:

Feed soil microbes

The rhizosphere is the place where plant roots grow. Huge and diverse populations of soil microbes (fungi and bacteria) live on and near plant roots. They feed on sugars and other compounds leaking from the plant roots. These beneficial microbes can antagonize and out-compete root pathogens, increase the organic matter content, serve as a food source for soil animals, and store carbon when they die.

1. Increase the diversity of plants aboveground to increase the diversity of microbial populations below ground. The result is a more complex and resilient soil ecosystem.

2. Keep it green and growing! Soil microbes need living plant roots during warm and cool seasons. The roots of dormant perennials, grasses, and cover crops support soil microbes which remain active through much of the winter.

Protect soil aggregates (crumbs)

3. Keep the soil food web working by disturbing the soil as little as possible. This helps to ensure that earthworm burrows, pore spaces, and soil aggregates remain intact and functioning. Frequent tilling can degrade soil structure.

4. Keep soil covered at all times to prevent/reduce soil erosion and nutrient run-off and protect soil aggregates and organic matter. Options include mulches, cover crops, and groundcovers.