Development of a Simplified Sampling Technique for Soil Fauna Extraction

Abstract

Human activities such as intensive agriculture and industries could weaken the soil quality. Traditional approaches of soil quality evaluations are mainly based on the use of physical, chemical and microbiological indicators. The importance of including soil invertebrates in soil assessments has been recognized in the recent past because these organisms enable to evaluate another dimension of soil quality which may not be measured by using physical and chemical indicators alone. The reason is that the soil organisms are interlinked with the physical environment and the soil processes. Attempts have been made to assess the soil quality using soil invertebrates as the indicators. Any such indicator should be accurate and sensitive to changes. Further, the associated techniques should be accessible and convenient to a range of users including scientist, farmers and land managers. Visible invertebrates as earthworms, enchytraeids and insect larvae have already been used in soil quality evaluations. However, their sampling and identification are challenging. This study focused on simplifying the sampling process for hand-sorting by reducing the soil sample volume (within 0-10 cm soil depth). A 0.5 l core sampler and a soil block of 15 × 15 × 10 cm (2.25 l) volume was compared against a reference soil block of 30 × 30 × 10 cm (9 l) volume (α ═ 0.05, t-test). Sampling was done in a Mahogany (Swietenia macrophylla) Plantation, Rubber (Hevea brasiliensis) plantation and a lawn dominated by Paspalum spp. in the low country wet zone of Sri Lanka. Sixteen samples each from 2.25 l block and 0.5 l core and four samples from 9 l block were taken from each system. Total count of the invertebrates visible under a hand lens (magnification- ×2/4) was recorded. There was no significant difference between 2.25 l block, and 83.33% of observations (p=0.643, 0.182, 0.063, 0.079, 0.052, 0.404, 0.356, 0.590, 0.125, 0.263) in the reference block. However, there was a significant difference between 0.5 l core sampler and the reference block in all the comparisons (p=0.000, 0.001, 0.000, 0.002, 0.005, 0.011, 0.015, 0.008, 0.000, 0.029, 0.002, 0.001). Therefore, it can be concluded that the soil block of 2.25 l can produce accurate data in soil fauna extraction. Therefore, time and effort required for sorting out soil fauna can be reduced by nearly four times by reducing the soil volume down to 2.25 l.

KEYWORDS: Soil quality, Soil invertebrates, Soil sampling, Soil volume, Hand-sorting