Development of a Simplified Sampling Technique for Soil Fauna Extraction

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-sortin

Soil Carbon Storage Potential of the Home Gardens Adjoining Selected Natural Forests of the Southern Sri Lanka

Conversion of forests to other land uses is inevitable despite the environmental issues associated with forest clearing. Tropical home gardens have long been identified as a land-use system analogous to forests from various perspectives. Carbon storage in the tropical forest soils is estimated to be nearly 32% of the global soil carbon. Although few in number, research conducted in Sri Lanka has shown that the home garden soils could store relatively a large amount of carbon. Present study was conducted in the low country wet zone of Sri Lanka (WL2) using the topsoil (0-15 cm) and subsoil (15-30 cm) samples taken from two sets of home gardens (HG) adjoining two natural forests (Mulatiyana and Wilpita) where latter was used as benchmark sites. Twelve samples each was collected from the topsoil and the subsoil under each system reaching a total of 96 samples for the four systems. The objective was to assess the potential of the home garden soils to sequester carbon as an alternative to the dwindling carbon storage in forest soils. Analysis of bulk density data of 12 samples each from the HGs and forests showed no significant difference (T-test, α=0.05) between the forests and the HGs for the selected soil depths. Therefore, the assessment of the systems was done in terms of the percentages of soil organic matter (SOM). All the comparisons were done using T test with α=0.05. For the topsoil, Mulatiyana HGs and the forest had mean SOM contents of 4.14%±0.98SD and 5.50%±0.71SD, respectively and, it was significantly different (p=0.001). On the contrary, Wilpita HGs and the forest had values 3.71%±1.6SD and 3.17%±0.059SD, respectively and, they were not significantly different (p=0.296). When the two forests and the home gardens were compared separately, Mulatiyana forest had significantly higher SOM content (p=0.000) over Wilpita forest while the home gardens had no significant difference (p=0.437). When the subsoil was compared neither Mulatiyana forest and the HGs (3.62%±0.64SD, 3.18%±0.70SD; p=0.072) nor Wilpita forest and the HGs (2.60%±1.01SD, 3.10%±1.14SD; p=0.268) had significant differences in the SOM contents. When the two forests and home gardens were compared separately, Mulatiyana forest had significantly higher SOM compared to Wilpita forest (p=0.008) while HGs had no significant difference (p=0.985). These results indicate that the soils of the home gardens adjoining the forests are capable of storing carbon almost up to the natural storage limit for a given locality. Hence, it can be envisioned that the carefully structured home gardens in view of capturing and storage of carbon could be a good alternative for the dwindling forests in the humid tropical environments.Keywords: Soil carbon, Home gardens, Low country, Wet zon