PatsPage

2nd in a series of soil articles.

Before leaving the previous edition of "Pats Page," I asked if readers knew what the symbol below represented.

This is the symbol for Soil Quality which embodies the circle of life (earth), the natural resources, their dependence on soil, and the human dependence on the health of it all. Two corn stalks represent agriculture and people working together to produce food and a bountiful, healthy life. The tree symbolizes all natural resources, including forests, rangelands, wildlands, and home gardens. The shaded background within the circle is the soil, the warm sustaining resource that is the foundation of all life. A circle of harmony and protection embraces these resources and the open sky (a raindrop) from which rain replenishes living things. Light from the sun's rays warms and energizes all.

What is soil quality?

Soil quality is a measure of how well the soil does what we want it to do. And what do we want it to do? Support plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation. The quality of a soil is an assessment of how it performs all of its functions now and how those functions are being preserved for future use.

Soil quality cannot be measured directly, therefore, indicators are used to provide clues. Indicators are measurable properties of plants and soil. They are often grouped as follows:

biological	Measuring the amount of living organisms by counting and identifying what organisms are present. Measuring activity levels of living organisms. Measuring cellular components such as the amounts of biological carbon or nitrogen in the soil.
chemical	These include tests of organic matter, pH, heavy metals, cation exchange capacity, and others.
physical	Physical characteristics that vary with management include bulk density, aggregate stability, and penetration resistance

The type of indicator chosen to evaluate soil quality depends on the soil function and the size of the area (i.e. field, farm, watershed, or region) in which the evaluation is made.

Why does soil quality matter?

Soil quality is important for two reasons. First, using a soil improperly can damage it and the ecosystem, therefore we need to match our use and management of the land to the soil's capability. Second, we need to establish a baseline understanding about soil quality so that we can recognize changes as they develop. By using baselines to determine if soil quality is deteriorating, stable, or improving, we have a good indicator of the health of an ecosystem. The ultimate purpose of researching and assessing soil quality is to protect and improve long-term agricultural productivity, water quality, and habitats of all organisms including people.

Factors that affect soil quality

Sediment Deposition	Sediment is solid material that is or has been transported from its site of origin by air, water, gravity, or ice to a field or low landscape position. Deposition occurs when the amount of sediment becomes greater than the carrying capacity of the force that is moving it. Sediment can either improve or degrade the soil upon which it is deposited. If fine-grained soil particles are deposited on sandy soils, the soil quality may improve. However, if coarser particles are deposited on fine-textured soil, the quality of the soil usually degrades over time.
Compaction	Soil compaction occurs when soil particles are pressed together, reducing the pore space between them. This increases the bulk density of the soil. Soil compaction is caused by tilling, harvesting, or grazing when the soils are wet. Compaction reduces the uptake of water and nutrients by plants by restricting their root depth. It affects the activity of soil organisms. Compaction decreases infiltration and thus increases runoff and the hazard of water erosion.
Salinization	Salinization is the process by which water-soluble salts accumulate in the soil. It may occur naturally or because of conditions resulting from management practices. Salinization is a concern because excess salts hinder the growth of crops by limiting their ability to take up water.
Soil Biodiversity	Soil biodiversity reflects the mix of living organisms in the soil. These organisms interact with one another and with plants and animals forming a web of biological activity. Soil organisms decompose plant residue and play a key role in nutrient cycling.
Available Water Capacity	Available water capacity is the amount of water that a soil can store that is available for use by plants. In areas where drizzle falls daily and supplies the soils with as much or more water than is removed by plants, available water capacity is of little importance. In other areas, however, where the plants remove more water than is supplied by precipitation, the available water supply may be a critical factor.
Pesticides	Pesticides are synthetic organic chemicals used to control weeds in fields and lawns, and unwanted or harmful pests, such as insects and mites that feed on crops. Pesticides can adversely impact human and animal health, contaminate surface and groundwater, and possibly cause adverse impacts on aquatic ecosystems.
Hydrophobicity	Soils that repel water are considered hydrophobic. A thin layer of soil at or below the mineral soil surface can become hydrophobic after intense heating (i.e. forest fire). The hydrophobic layer is the result of a waxy substance that is derived from plant material burned during a hot fire. The waxy substance penetrates into the soil as a gas and solidifies as it cools, forming a waxy coating around soil particles. Hydrophobic soils repel water, reducing the amount of water infiltration. Decreased infiltration into the soil results in damaging flows in stream channels. Erosion increases with greater amounts of runoff, and much of the soil's fertile topsoil layer is lost.

How do you manage for soil quality?

Add organic matter. Soil organic matter is an energy source for organisms that have an important role recycling nutrients for plants. It also is a nutrient source, nutrient retainer, and a contributor to structural stability in soil.

Avoid excessive tillage. Tillage degrades organic matter, disrupts soil structure, and can cause compaction.

Be careful in your use of fertilizers and pesticides. They can harm non-target organisms and pollute water and air if they are mismanaged.

Increase ground cover. Ground cover protects the soil from wind and water erosion, and from drying and crusting.

Increase plant diversity. Diversity is beneficial for several reasons. Each crop contributes a unique root structure and type of residue to the soil. A diversity of soil organisms can help control pest populations and a diversity of cultural practices can reduce weed and disease pressures.

Soil Quality Terms

aggregate stability	a measure of how resistant soil aggregates (many soil particles held together in a small mass) are to destruction.
bulk density	the density of soil determined by dividing the weight of the soil by its volume.
cation exchange capacity	the capacity of soil to hold nutrients for plant use.
crusting	soil crusts are relatively thin, somewhat continuous layers of soil surface that often restrict water movement, air entry, and seedling emergence from the soil.
infiltration	the process of water entering the soil.
organic matter	any material that is part of or originated from living organisms.
pH	a measure of the acidity or alkalinity in the soil. pH ranges from 3.5 (extremely acid) to 9.0 (strongly alkaline).