The soil tests

1 Ground cover

Toss a coat hanger quadrat (squared) onto the ground at random and estimate the proportion of bare soil within the frame. Subtract this from 100% to calculate ground cover. Examine surface litter or mulch to estimate its depth. On the test sheet note the grade which best matches your soil. Both ground plants and mulch contribute organic matter to the soil that will feed soil animals and microbes. Roots of ground plants also help maintain good soil structure.

2 Penetrometer

Push a penetrometer (3mm wire) into the soil as deep as you can with modest effort. Record the depth of penetration on your assessment sheet. If you hit a rock or tree root, choose another spot. The easier it is to penetrate the soil, the better the deep root development and water infiltration.

3 Infiltrometer

Push the infiltrometer tube (50mm sharpened plastic tube)one to two cm into the soil, avoiding cracks and other holes in the ground. Gently fill the tube with water and note the time; after 60 seconds note how far the water level has fallen. A higher rate of infiltration will mean your soil will absorb rainfall more quickly, resulting in less run off and erosion.

4 Diversity of soil life

Toss your coat hanger quadrat on the ground in an area not disturbed by earlier tests. Examine the surface for soil animals and then carefully sift through the litter. Note how many different varieties of soil animals you see such as ants, beetles, spiders, slaters, millipedes, mites etc. It is the variety that is important, not the numbers - a column of ants counts as one variety.

5 Root development

With your spade cut a 20 cm square hole to a depth of 20 cm. Lift the soil out, trying to keep it in one block, and place it on the plastic sheet. Examine the distribution of plant roots and complete the card. The distribution of fine roots will show whether soil structure is restricting the plants’ access to nutrients.

6 Soil structure

Break a small handful of soil away from near the original surface of the block you have dug up and examine the size and arrangement of the soil aggregates or ‘crumbs’ (discrete clumps of soil particles). Under firm finger pressure soil should be friable, breaking into crumbs varying in size up to about 10 mm. There should also be evidence of root penetration throughout. Poor structure may be seen either as overly solid soil (hard crumbs, soil layers or clods) or as very loose soil (absence of even small crumbs, as for example in beach sand). Good structure results in easy passage of air and water, an ability to hold water and superior resistance to erosion.

7 Slaking or aggregate stability

Select three or four pea-sized soil aggregates from about 5 cm depth, avoiding small stones. Drop the aggregates into 125 ml water in the small wide mouthed jar and allow to stand for one minute. Observe if the aggregates break apart or stay intact. If they are intact after one minute, gently swirl the bottle several times and observe again. If they are still intact, swirl the bottle vigorously and check again. Aggregates of a healthy soil are normally more stable than those of a less healthy one. Poor aggregate stability is associated with greater susceptibility to erosion. Repeat the test om a sample from a depth of 20 cm.

8 Earthworms

Break up your entire soil block into crumbs and place any worms found into a jar. When done, count any worms that are longer than 25 mm, record on the sheet and return the worms to the hole. Higher numbers of earthworms indicate conditions that are favourable (more organic matter, high pH, low chemical residues). Mostly these are also conditions favourable for plant growth.

9 Soil pH

Take two small samples of soil from the side of the hole, one from 5 cm and one from 20 cm depth. Test each sample for pH, following the instructions included in the kit. Acidity has a strong effect on the ability of plants to take up soil nutrients as well as upon the wellbeing of soil organisms.

10 Leaf colour

Examining your crop, trees or pasture at the soil test site may reveal plant health problems not identified by the completed soil tests. In crops or orchards examine fully formed leaves about four leaves back from the growth tip. (Young leaves at the tip are often naturally pale or red leaves while old leaves nearer the stem may show mottling that is normal).

SOME EXTRA (OPTIONAL) TESTS

Calico strip test for soil microbes

Microbes in the soil (bacteria, protozoa and fungi) play a major role in the breakdown of soil

organic matter. Microbial activity can be estimated by measuring the rate of breakdown (‘rotting’)

of calico. Cut unbleached and washed calico into 20 cm squares. Using a felt tip pen draw a line

across the square 5 cm from one edge. Make a cut in the ground to a depth of 15 cm with the spade

and, again using the spade, insert the calico so that the marked line coincides with the soil surface.

Arrange the top 5 cm of calico vertically in the litter layer, if present. Use at least 5 calico strips at

each test site and leave in place for three weeks. Gently retrieve and rinse in a kitchen sieve, to

remove attached soil. Place over a piece of graph paper and estimate the percentage area of the

calico that has completely decomposed. The more the calico has rotted away the healthier the

community of soil organisms.

Bioturbation

Bioturbation is the mixing of surface organic matter into the soil profile by organisms. On the side

of the hole dug at Test 5, observe the distribution of the darker soil colouration that is due to organic

matter in the profile. Note the depth to which you can detect this darker soil and record on your

sheet.

Erosion

Take a 50 cm length of 100 mm x 50 mm timber and place it on the ground, across the slope, near

the bottom of a long incline. After each major rainfall event check the wood for a build up of soil on

the upper side.