Soil is 90% rock and minerals and up to 10% organic material or humus. A fertile soil contains 4 to 10% humus. If the humus content of a soil is below 2%, that soil cannot support plant life. Humus holds and releases nutrients to plants and microorganisms and helps retain water. It also attracts earthworms, sowbugs, centipedes, ants, and other insects which digest it.

Compost can be added to soil to increase its organic content. Compost helps bind heavy metals and breaks up heavy clays and salts. A higher percentage of organic matter in a soil will help with water retention in a drier climate. Humus needs high aeration and adequate moisture to be available to plants. If humus is too dry, it will be inactive. If it is too wet, it will cause anaerobic conditions.

The relative health and viability of a soil can be accessed through on-site observation and conducting simple evaluations.

METHOD 1
Identify plants on site

Look at the soil. Identifying which plants are being supported by it (especially spontaneous vegetation such as common weeds and native plants) is a good way to understand the soil’s structure, its pH, a history of its disturbance, as well as the possible presence of nutrients and organic content. You can benefit from reading people’s work on this matter:

Weeds and What They Tell by Ehrenfried E. Pfeiffer
Weeds and Why They Grow by Jay McCanan

METHOD 2
pH test
to understand the relative pH of your soil

materials needed:

distilled water (insures neutral pH)
four clear jars
red cabbage
soda lime
vinegar
soil

Red cabbage juice is a good indicator of pH. In one quart of distilled water, gently boil up to ¼ head of red cabbage until the cabbage loses color. Allow the water to cool and compost the spent cabbage. Pour cabbage juice into four equal parts into four clear jars. In one jar squeeze in 1 tablespoon (T) of vinegar. It will turn a bright pink and represents the acidic side of the scale. In the second jar stir in 1 T of lime. It will turn bright blue and represent the alkaline side. The cabbage juice (purple) by itself represents a neutral pH of seven. In three jars mix in 1 T of soil. To make this scale visual, arrange the jars with vinegar on the left, cabbage in the middle, and lime to the right. Place the fourth jar with the soil and cabbage juice where it belongs in the visual scale.

Many plants enjoy a neutral pH, but there are some that require a more acidic soil and others that can tolerate a more alkaline soil. It is important to know what you intend to or are already growing for this test to be relevant. Briefly, compost can be added to soil to help drop the soil pH. Lime can be added to raise it.

Research your plants’ needs before amending your soil to change its pH!

METHOD 3
Flotation test
to better determine soil composition

materials needed:

soil
newspaper
glass jar
water
detergent
ruler

Take one cup of soil from a depth of 6” from the area you want to test. Spread it on some newspaper to let it dry out. When dry, sift it through a colander or rough screen so rocks and large organic material get screened out. Put the sifted soil in a jar, pour in water to fill and one 1 teaspoon of soap. Cap and give a few vigorous shakes until all materials are mixed. Allow the contents to settle. The contents will settle out according to weight. Measure the total solids using the ruler. Then measure each layer of silt and sand. Divide the amount of each of these layers by the amount of the total sample for percentage of silt, clay, humus and sand. Refer to

METHOD 4
Percolation test
to see your soil’s structure and composition

materials needed:

shovel
water
watch

procedure:

Dig a hole of at least a shovel length’s depth and width. Pour in one quart of water and time how long it takes to soak in completely. Repeat this with a few other sites for comparison, say a sandier one, a rockier one, one with a lot of clay or a very compacted site. If available, also do this with some high-grade compost.

A soil with more humus will not drain as quickly as a sandy soil nor so slowly as compacted or heavy clay soil.

METHOD 5
Soil ribbon test
to get a feel of your soil’s structure and composition

Thank you Colorado State University for this:

Copyright 2011 Nance Klehm