Soil Quality

As defined by the Soil Science Society of America soil is a “complex mixtures of minerals, water, air, organic matter, and organisms, which form at the surface of land.” In other words, soil is the thin outermost layer of the Earth’s crust that forms the basis for existence of life on this planet. Like our own skin, we can’t live without the soil but at the same time we often take it for granted!

Soil is a precious resource, and we can all do our part to ensure that healthy soil is part of the legacy we leave for future generations.

Understanding soil quality is very important – it is our single best indicator of sustainable land management.

Soil quality is the capacity of a soil to function as part of a healthy agricultural or natural system.This means:

  • Sustaining biological productivity (ie: growing healthy pastures and vibrant gardens)
  • Maintaining air and water quality (ie: filtering polluted runoff and keeping ground and surface water clean)
  • Promoting plant, animal, and human health (ie: promoting plant resistance to diseases and pests, breaking down toxins, and decomposing waste products).

What can I do to protect and improve soil quality on my farm?

 1. Keep it covered

Bare soil is very vulnerable to loss by wind and water erosion, and compaction from rain.

Bare soil in pastures, paddocks, and driveways is quickly lost as water moves across the surface. Loose soil is carried into streams and rivers, and eventually makes it into Puget Sound. Soil is a valuable asset on the farm, but quickly becomes a pollutant when it gets in the water!

In the summer months, bare dry soil is easily carried from your farm to your neighbor’s with the wind. Re-seed bare spots or plant cover crops and keep valuable soil at home where it belongs!

Bare soil is also more vulnerable to compaction from rain, livestock, or vehicles.

 2. Be gentle

Wet soil is most vulnerable to compaction from trucks, tractors, and hooves.

Compaction damages the natural soil structure and delicate plant roots struggle to grow through hard and compacted soil. As a result, plants are often stunted or nutrient starved in these conditions. Plants depend on roots to draw nutrients from the soil and when root growth is restricted, access to nutrients is restricted. Overgrazed pastures are often suffering from compaction and weeds are much more competitive than pasture grasses in compacted soils. By allowing overgrazing of pastures, you are increasing the weed pressure and putting grasses at a disadvantage.

Water soaks into compacted soil much more slowly, especially after a heavy rain event. Water moves across the surface of compacted soils instead of filtering down through the soil and into groundwater. This increases the chances of flooding, standing water, and pollution of to streams and rivers.

Repeated tillage can break-down the natural soil structure that is so important for healthy roots and soil microbes. Consider reducing or eliminating the roto-tiller from your gardening routine, and keep the soil protected with mulches and cover crops.

Here is a short video about no-till vegetable farming:

 3. Feed the soil

Add manure, compost, and cover crops to your gardens and pastures.

Plants remove nutrients like nitrogen, phosphorus, potassium, and calcium from the soil as they grow. When plants die and decompose, these nutrients are returned to the soil and recycled. If the plants are harvested and removed, the nutrients are removed with them. Adding compost, manure, or fertilizers back to the soil is important to keep the soil healthy and the plants growing.

Soil organic matter is made up of plant and animal materials in various stages of decomposition (manure, compost, dead and decomposing plants and insects, etc.). While soil organic matter makes up only about 5% of the total soil, it plays a very important role in soil quality! A soil high in organic matter is more resistant to damage and recovers more quickly from tillage and compaction, and contamination from herbicides or other toxins.

Increasing the organic matter in your soil benefits the soil in many ways:

  • loosens a “heavy” clay soil to improve drainage and make it easier to work
  • increases moisture and nutrient holding capacity in a sandy soil
  • improves plant resistance to disease
  • provides a slow-release source of plant nutrients and minimizes the need for synthetic fertilizers
  • binds to toxins in the soil so they are quickly degraded by soil microbes and do not pollute wells and streams
Most soils in western Washington are acidic due to the climate and the fact that many of the areas we use for gardens and pastures were originally forested. The long-term use of ammonia based fertilizers can also increase soil acidity. Most pasture grasses and agricultural crops thrive in near neutral soils (pH ~ 6 to 7.5), and certain nutrients like iron and phosphorus are less available to plants in very acidic or alkaline soils. Lime can be used to raise the pH of acidic soils and add calcium (an essential plant nutrient). Most pastures in Snohomish County benefit from yearly applications of 1-2 tons of lime per acre.  For more information, see Soil Fertility.