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Shifting Cultivation Effects on Soil Fungi and Bacterial Population in Chittagong Hill Tracts, Bangladesh

Sohag Miah
Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong 4331, Bangladesh

Soma Dey
Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong 4331, Bangladesh

S. M. Sirajul Haque
Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong 4331, Bangladesh

Abstract/ Executive Summary:

A study was conducted at two pair sites of Chittagong Hill Tracts in Bangladesh to find out the effects of shifting cultivation on soil fungi and bacterial populations. The first pair of sites with shifting cultivation and village common forest-managed by the indigenous community was at Madhya Para in Rangamati district and the second pair of sites with the shifting cultivated land and village common forest at Ampu Para in Bandarban district of Chittagong Hill Tracts. At both the locations with two different land use, soil textures in surface (0−10 cm) and subsurface (10−20 cm) soils varied from sandy loam to sandy clay loam. Soil pH and moisture content were lower in shifting cultivated land compared to village common forest. The results also showed that both fungal and bacterial population in surface and subsurface soils was significantly (p ≤ 0.05) lower, in most cases, in shifting cultivated land compared to village common forest at both Madhya Para and Ampu Para. At Rangamati and Bandarban in shifting cultivated lands, Colletrotrichum and Fusarium fungi were absent and all the bacterial genus viz. Coccus, Bacillus and Streptococcus common in two different locations with different land uses. Common identified fungi at both the land uses and locations were Aspergillus, Rhizopus, Trichoderma and Penicillium. Further study can be done on the other soil biota to understand the extent of environmental deterioration due to shifting cultivation.

Keywords: Shifting cultivation; Fungi; bacteria; Soil biological properties; Village common forest; Chittagong Hill Tracts; Bangladesh

Location: Chittagong Hill Tracts in Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Bacteria, Fungal Disease

Objectives:

The most important symbiosis is between leguminous plants and bacteria of the genus Rhizobium found in the nodules on roots of the species of Leguminosae family. The rhizobia infected and interacted with around 13 thousands different legume species. The cyanobacteria can fix nitrogen and carbon dioxide directly from the atmosphere and can colonize bare rock surface and initiate soil formation. The cyanobacteria forming lichen association with fungi also can act as primary colonizer and initiator of soil formation.

Methodology:

Site description: The study was conducted in shifting cultivated and village common forest lands of two hill districts, namely Rangamati on 13 March and Bandarban on 9 August, 2008. Village common forests is also known as “mouza” forest, and managed by indigenous people in CHTs with the aim to meet own requirements. Village common forest is the better representation of once rich natural vegetation in CHTs, because at present natural forest does not exist in many areas in this mountainous region due to various human activities. Soil samples were collected from two pair sites representing shifting cultivated land and nearest village common forest land. Rangamati Shifting cultivated land of the first pair of site was beside Manikchari-Khagrachari road at Duluchari Para under Kutukchari union of Naniarsori Upazila in Rangamati hill district at 22⁰42.1"32′N latitude and 92⁰05.3"81′E longitude on the north-east aspect on the upper part of a gentle hill slope. In shifting cultivated land, about 70% land was without any tall vegetation; almost 95% land area without litter and exposed to sun light with the presence of few thickets such as Saccharum spontaneum (kash), Mimosa pudica (lajjabati) and Eupatorium odoratum (assam lata). Last year shifting cultivated crops were Curcuma longa (turmeric) and Oryza sativa spp. (paddy), and existing crops consisted of Lablab purpurens (bean) and Manihot esculenta (kasava) as vegetables. Musa paradisiaca (banana), Artocarpus heterophyllus (jackfruit) and Mangifera indica (mango) seedlings and 2-3 year old Tectona grandis (teak) saplings are on the border of the land only. A patch of 7–8 year old Albizia procera (shil koroi) with a maximum height of 16 m was present on the south-east side of this shifting cultivated area. The compared village common forest was situated 3 km away from shifting cultivated land at Madhya Para near Ban Bihar at 22⁰42.343′N latitude and 92°05.40′E longitude on north east aspect of sites. Vegetation on the hill was not uniform and consisted of Dipterocurpus turbinatus (garjan) and Melocanna baccifera (muli bamboo) with a few shrubs such as Clerodendrum viscosum (bhat), Garcinia cowa (kaw), etc. giving 100% canopy coverage as top storey. Melocanna baccifera gave 60% coverage as under storey. Bandarban The second pair site was situated at Ampu Para beside Chimbuk-Thanchi road on the eastern aspect under Ruma upazila of Banderban hill district. Here, shifting cultivated land was on moderate or steep hill slope with scattered vegetation, such as Bambusa tulda (mitinga bans), Albizia richardiana (raj koroi), Anarzicus accuminata (koshoi), Ficus hispida (dumur), Gmelina arborea (gamar), Artocarpus lacucha (borta), Smilax zeylanica (smilex), etc. The village common forest was at Ampu Para at 21⁰58.7"38′N latitude and 92°17.995′E longitude. This village common forest was situated 12 km away from the shifting cultivated land. Over the entire village common forest area, species composition was variable in patches with the presence of both natural and artificially planted species. Naturally growing forest was comprised of Artocarpus chaplasha (chapalish), Dillenia indica (chalta), A. accuminata, E. odoratum, several varieties of Syzygium spp. (jam), A. procera, etc. Planted species were T. grandis, G. arborea and Schima wallichii (kanak). However, S. wallichii was the dominant species in both natural and planted forest areas. Soil sampling and analyses The composites of 5 soil samples were collected randomly from soil depth of 0−10 cm and 10−20 cm covering each of the land use types: shifting cultivated and village common forest lands. Each soil sample was put in labeled poly bag sterilized with 95% ethyl alcohol. In the laboratory, the sieved dry soil sample was used for the determination of soil texture by Bouyoucos hydrometer method according to Huq and Alam (2005) and moist soil pH at 1:2 soil-water ratios by TOA pH meter. A portion of the collected soil was kept in incubator at 4⁰C for the determination of microbial population. Soil texture determination For determination of soil texture, 25g of air-dried sample was taken in a 600-mL tall beaker, added 30 mL of concentrated H2O2 and kept over night covering with a clock glass. Then 200-mL of distilled water and 5 mL of 10% calgon solution were added to the contents in beaker. The contents were then removed to a 1000-mL sedimentation cylinder with distilled water using wash bottle and volume made up to the mark. Another blank set was arranged to add all the materials without soil. Temperature of the soil suspension in cylinder and the blank set was taken. Then the content was thoroughly mixed repeatedly. Hydrometer reading was taken at 40s, 4 min and 2 h from the start of settling of soil particles. From the observed hydrometer readings, percentage of each sized soil particles was calculated.

Source of Information: Journal of Forestry Research (2010) 21(3): 311?318

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Achievement/Findings:

Shifting cultivation is not beneficial for the soil environment in any way. This cultivation system reduces soil moisture content and populations of fungi and bacteria as well as their varieties drastically in soil. In this study, the abundance and varieties of only two life forms have been explored. Further study is needed in this tropical region to understand further impacts of shifting cultivation on the myriad of organisms, which play many important beneficial roles in the soil environment.

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