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Observe & Interact: Soil Health Card

HEALTHY-SOIL
Healthy soil is crucial for a productive garden. Photo by Kel Buckley

The Northern Rivers Soil Health Card was developed as a practical tool for the region’s farmers and landholders to use to monitor the health of their soils. While it was developed in partnership with NSW Agriculture, it’s got lots to offer home gardeners all around the country who want to better understand soil health.

The soil health card lists 10 straightforward visual tests performed with simple equipment and which can be carried out by one person. The card, which can be found online and printed out, provides space for you to record important details regarding the test site, as well as space to rate your own soils after carrying out the tests. By testing regularly and keeping the cards, you can build up a record of your soil health and get a better longterm picture of what’s happening beneath your feet, and importantly, why it’s happening.

Regular testing will show improvements in response to more sustainable practices, and allow early detection of developing soil problems. The soil health card is not intended to replace any regular testing you may already carry out, it is simply another tool to help you understand your soils and their productivity.

Before You Start      

You will need to make three simple pieces of test equipment. First you’ll need a wire quadrat, which is a square frame used to isolate a standardised area to study, and made simply by stretching a wire coat hanger into a square shape. It is used to obtain an accurate measure of anything found there. You will use it to assess the amount of plant cover and then again to record the variety of animal life in the leaf litter.

Next you’ll need a penetrometer to test the hardness of your soil, sometimes referred to as how compacted it is. You can purchase expensive sophisticated penetrometers, but you can easily make your own using a 40-centimetre length of heavy-gauge fencing wire. Use 15 centimetres of the length to twist into a sturdy a handle, and on the remaining 25 centimetre length, make file marks every two centimetres from the bottom end.

Lastly, you’ll need an infiltrometer, which measures the rate at which a fixed volume of water soaks into the soil. Cut a nine-centimetre length of poly pipe which is 50 millimetres or more in diameter (remembering the larger the diameter, the more water you’ll need to use). Bevel the bottom edge to make it easier to push into the soil. Cut and mark a seven centimetre section (an old timber ruler is great because it won’t need marking), and glue to the inside of the pipe so that the zero-centimetre mark is level with the top of the tube. That means, when it’s pushed two centimetres deep into the soil, the seven-centimetre mark will sit flush with the top of your soil.

What You’ll Need

As well as your three homemade pieces of equipment, you’ll need a clipboard and pencil, a test results sheet for each of the tests planned (print extra copies of pages 8 and 9 from the downloadable PDF), a spade, a small plastic sheet, a soil pH kit, a wide-mouth jar marked to show 125 ml, water and something that will allow you to measure time in seconds – this might be a watch with a second hand or using the stopwatch app on your smartphone.

When And Where To Test

Best results will be obtained in autumn, two to 10 days after good rain. To allow comparison of results from year to year, sample at the same time of year and under similar conditions. Avoid taking samples from overly wet soils or during drought, at times of extreme high or low temperatures, or within a few weeks of fertiliser or lime applications.

It’s recommended you start with two sites, choosing one site which represents your best soil and the other which represents your worst area. This will give you a good overview of how the tests relate to soil conditions in your patch. Depending on how big your property is, you can then select other areas in order to get a broader understanding of the health of all of your soils.

soll-health-card
soil

This page, clockwise from top left You can download and print the soil health card and the three required tools are easy to make; How quickly water soaks in is indicative of structure and soil type; Observing plant leaves can tell you a lot about what’s happening beneath the surface; A slake test measures the stability of soils when wet. Photos by Kel Buckley

The Soil Tests

GROUND COVER

Toss your coat hanger quadrat onto the ground at random and estimate the proportion of bare soil within the frame. Subtract this from 100 percent 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.

PENETROMETER

Push your homemade penetrometer 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.

INFILTROMETER

Push the infiltrometer tube two centimetres into the soil, taking care to avoid 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.

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.

ROOT DEVELOPMENT

With your spade cut a 20-centimetre-square hole to a depth of 20 centimetres. 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.

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.

SLAKING OR AGGREGATE STABILITY

Select three or four pea-sized soil aggregates from about five centimetres depth, avoiding small stones. Drop the aggregates into 125 ml water in the small, widemouthed 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 jar several times and observe again. If they are still intact, swirl the bottle vigorously and check again. The 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 with a sample from a depth of 20 centimetres.

EARTHWORMS

Break up your entire soil block into crumbs and place any worms you find into a jar. When done, count any worms which are longer than 25 millimetres, 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). In most cases, these are also the conditions which are favourable for strong plant growth.

SOIL PH

Take two small samples of soil from the side of the hole you dug, one from five centimetres and one from 20 centimetres 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 the organisms in the soil.

LEAF COLOUR

Examining your plants and trees 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.

results
A basic soil test kit. Photo by Kel Buckley

Understanding The Results

Once you’ve performed and recorded the results of some or all of the 10 recommended tests, the card provides information to help you understand the scores, the situations the results might indicate and, if they’re low, possible causes and ways to rectify it. For example, slow water infiltration could indicate a high proportion of clay content, soil compaction, a possible loss of topsoil, poor soil structure, a lack of earthworms or surface crusting. But by carrying out multiple tests and observing the way the results interact with each other, you’ll begin to develop a really good understanding of the health of your soil and what you could be do to improve it.

This soil health card was developed as part of the Good Soil Project and the Good Worm Project, initiatives of Tuckombil Landcare Inc. in partnership with NSW Agriculture and the Natural Heritage Trust. Download it at www.soilcare.org

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