Field Guide. cropping and pastoral grazing on flat to rolling country.

SOIL INDICATORSEarthworm counts under <strong>cropping</strong> Sort carefully through the soil sample used to assess soil structure,<strong>and</strong> count the earthworms found in a 5 minute search. Earthwormsvary in size <strong>and</strong> number depending on the season, so for year-to-yearcomparison earthworm counts must be made at the same time ofyear, <strong>and</strong> preferably during the winter. The class limits for earthwormnumbers given opposite are based on the probability that you willfind only two-thirds of the worms present during a 5-minute search.(Earthworm numbers are commonly reported on a square-metre basis.A 20 cm cube sample is equivalent to 1/25 square metre <strong>and</strong> so thenumber of earthworms counted should be multiplied by 25 to convertto a square-metre basis. If your sample depth is only 0-10cm, thesame class limits <strong>and</strong> conversion factors apply, because commonearthworms are most abundant in the upper topsoil.)EARTHWORMS PLAY A MAJOR ROLE, through their burrowing, feeding<strong>and</strong> casting, in decomposing <strong>and</strong> cycling organic matter, <strong>and</strong> in supplyingnutrients. They can also improve soil porosity <strong>and</strong> aeration, waterinfiltration <strong>and</strong> conductivity, aggregate size <strong>and</strong> stability, reduce surfacecrusting, <strong>and</strong> increase root growth <strong>and</strong> subsequent grain yield.24 VISUAL SOIL ASSESSMENT: Volume 1