What’s the purpose of this test? This test is used to illustrate that soils rich in organic matter are healthy, living soils that support lots of different types of organisms. The test needs to be performed during the rainy season when organisms are active.
This exercise will make most sense to farmers if a discussion of the soil food web is part of the exercise.
For a good comparison, collect samples from healthy and unhealthy soils. Healthy soils are collected from areas with lots of organic matter build-up (forest, hedgerow, home garden, etc).
protocol by Steve Vanek
Materials
- Shovel with square tip for digging a regular, square hole.
- Knife or machete for trimming the edges of a hole
- Ruler, at least 20 cm long, to measure the dimensions of the hole. Sometimes two 20- cm rulers can be taped to form a right angle, which makes it easy to measure the hole precisely.
- Nylon grain bags or other similar strong sack to collect soil before looking for macrofauna
- Trays to use for distributing and searching soil for macrofauna
- Paint brush and water
- Tweezers or forceps
- Vials or cups of water to put the organisms into
Procedure:
- Using a ruler or small quadrat, mark out a 20 x 20 cm (square); using sticks for corners. Try to avoid heavy footsteps (loud noise on soil surface), as some macrofauna (especially large earthworms, with deep vertical burrows) can escape fairly quickly.
- Using a flat edge spade or shovel, excavate the soil quickly into a large plastic sack. Try to ensure from the start that the walls of the pit are vertical and excavate the pit in as few shovel loads as possible to avoid damaging macrofauna.
- Hand-sorting of macrofauna from soil: Find a comfortable place to work that is well lit. Scoop handfuls of about 500 mL, onto trays to sort through the soil, use tweezers to gently pick out any living thing that is visible , such as earthworms, ants, termites, beetles, spiders, and insect larvae. A team of at least 3-4 people handling each sample bag should be able to finish sorting a sample in 20 to 40 minutes, depending on the number of organisms encountered. One challenge is to not undercount (i.e., become rushed or sloppy) as one grows tired of sorting.
- Separate soft bodied organisms: Place soft-bodied organisms (earthworms, slugs) in one specimen cup. Any other organism else goes into another specimen cup
Count: If you want a more scientific assessment the macrofauna can be sorted and counted. Typically, sorting to the level or order (i.e., beetles, ants, spiders, etc.) is sufficient for understanding the functional composition of soil macrofauna communities, but further identification is useful for better understanding impacts on diversity.
It is important to note that macrofauna data can often be quite “noisy” and conclusions are not always absolute or clear-cut. For this reason, analyses are often best conducted at the level of orders and/or with the most abundant taxonomic groups (often earthworms, ants, and beetles).
An excellent field key which is simplified to capture most orders of soil macrofauna is available from resources prepared by IRD / FAO. This guide is reproduced as appendix B of this manual and is also available at (http://www.fao.org/3/a-i0211e.pdf ; or also http://ftp.fao.org/docrep/fao/011/i0211e/i0211e.pdf).