Evaluation of the “bait-lamina test” to assess soil microfauna feeding activity in mixed grassland

The soil fauna plays an important role in regulating nutrient cycling through predation and comminution of organic residues. The bait-lamina test was proposed as a practical mean to assess soil faunal feeding activity. The test consists of vertically inserting 16-hole-bearing plastic strips filled with a plant material preparation into the soil. We assessed the value of the bait-lamina test in the mixed grassland ecoregion of Canada, using 5-year-old seeded grass field plots. There were five treatments of grass communities, i.e. monocultures of (1) Russian wild rye, (2) switchgrass, (3) green needlegrass, or (4) western wheatgrass, and (5) a grass mixture of western wheatgrass + green needlegrass + switchgrass + little blue stem, which were distributed in four complete blocks, and six bait mix treatments, i.e. bait made with ground tissue of (1) Russian wild rye, (2) switchgrass, (3) green needlegrass, (4) western wheatgrass, (5) alfalfa, or with (6) wheat bran, which were randomized in each plot. Bait-lamina strips were used in groups of five strips inserted in the soil; they were equally spaced across the inter-row. The analysis revealed a marginally significant effect (P = 0.065) of plant community on soil faunal feeding activity with more activity in mixed grass species compared to green needlegrass plots. Bait flavour had no significant effect (P = 0.22) on feeding. More (P < 0.0005) feeding activity was detected close to the soil surface (0-5 mm deep) than at 20 mm below the surface and at deeper depths. Feeding activity was relatively low over the 65-day period of the test (13 June to 17 August 2005), with 8.3% and 2.0% of the lamina (holes filled) showing signs of feeding in the 0-5 and 5-15 mm soil layer. We conclude that the bait-lamina test is appropriate to assess the activity of surface litter processing fauna in mixed grassland, but it is not a good indicator of the decomposition occurring in the soil matrix, where most litter is produced. We recommend the use of a large number of replicated bait-lamina strips and a whole growing season incubation period in soils of the semiarid prairie ecoregion where the surface litter layer is thin and faunal saprobes are relatively scarce.