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Effect of Shifting Cultivation on Soil Physical and Chemical Properties in Bandarban Hill District, Bangladesh

Khandakar Showkat Osman
Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong-4331, Bangladesh

M. Jashimuddin
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

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

Abstract/ Executive Summary:

This study reports the effects of shifting cultivation at the slashing stage on soil physicochemical properties at Bandarban Sadar Upazila in Chittagong Hill Tracts of Bangladesh. At this initial stage of shifting cultivation, no general trend was found for moisture content, maximum water holding capacity, field capacity, dry and moist bulk density, particle density for some chemical properties between shifting cultivated land and forest having similar soil texture. Organic matter was significantly (p≤ 0.05) lower in 1-year and 3-year shifting cultivated lands and higher in 2-year shifting cultivation than in the adjacent natural forest. Significant differences were also found for total N, exchangeable Ca, Mg and K and in CEC as well as for available P. Slashed area showed higher soil pH. Deterioration in land quality starts from the burning of slashing materials and continues through subsequent stages of shifting cultivation.

Keywords: Chittagong Hill Tracts; Natural forest; Shifting cultivation; Soil properties

Location: Bandarban hill district, Bangladesh

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Physico-Chemical

Objectives:

The present study aimed to determine the effects of shifting cultivation at the slashing stage on soil properties in Bandarban hill district. Cutting of all the naturally coming vegetation as first the step of land preparation for shifting cultivation is termed as slashing.

Methodology:

Study area selection and soil sampling Our study area were in Bandarban Hill District of Bangladesh (22°20′0″ N and 92°35′0″ E) where local ethnic people practice shifting cultivation or jhum for their livelihood. To select representative study sites, a preliminary survey was done in the shifting cultivated area and adjacent natural forest of Bandarban Sadar Upazila. Assistance was taken from local people and Forest Department personnel to identify study sites exposed to years of shifting cultivation yet adjacent to natural vegetation. Three paired sites were selected on mid-elevation sites on hill slopes, namely 1-year shifting cultivated land at Na-mile village, 2-year shifting cultivated land at Shoalok village, and 3-year shifting cultivated land at Aatmile village under Bandarban Sadar Upazila, each with adjacent naturally coming vegetated secondary forest. Soil samples in the shifting cultivated land and adjacent natural forest were taken at least 30 m from the boundary to avoid interaction between the two types of land use. At the time of soil sampling, shifting cultivated lands at all three locations were covered with fresh slashed materials, with the aim to dry them on exposed sunlight, after which all the materials would be burnt before sowing seeds on the land as various steps of cultivation. From each land use of each paired site, nine soil samples were collected from depths of 0–15 cm with three replications during the first and second week of February 2009. Soil samples were placed in labeled, air-tight plastic bags and carried to the laboratory for analysis. For the determination of bulk density, one undisturbed soil core was collected separately from the upper soil layer for each land use at each paired site. Soil analysis In the laboratory, soil texture of the sieved, dry soil samples was determined by the Bouyoucos hydrometer method (Huq and Alam 2005). Moisture content, maximum water holding capacity and field capacity were determined from core samples collected for bulk density. The weight of field-moist and oven-dry soil in the core was divided separately by core volume to determine bulk densities of moist and dry soil. Particle density was determined by taking two 10-ml cylinders, the first filled with water up to the 10 ml mark. In the second cylinder, 2 g of soil burnt in a furnace was taken and water from the first cylinder poured until the water reached the 10 ml mark. The remaining water in the first cylinder indicated the volume of soil particles. The weight of soil divided by volume determined soil particle density. Soil organic carbon and organic matter were determined by the loss on ignition method according to Ball (1964). Moist soil pH was determined using a TOA pH meter in triplicate at 1:2 soil water ratios and total nitrogen was determined by the micro Kjeldahl method (Jackson 1973). Exchangeable calcium and magnesium were determined by the EDTA method. Potassium concentration was quantified using a flame photometer (Jackson 1973). Cation exchange capacity (CEC) was determined after extraction with 1 N ammonium acetate solution (Black 1965). Available phosphorus was extracted with Bray and Kurtz No.2 extractant and measured by SnCl2 reduced molybdophosphoric blue color method using a spectrophotometer (Jackson 1973). Statistical analysis Replicated data were analyzed statistically for variance and one-way analysis of each parameter to determine significance level for means between two land uses using the Statistical Package SPSS 12.

Source of Information: Journal of Forestry Research (2013) 24(4): 791?795

Article Link (Online Journal): DOI 10.1007/s11676-013-0368-3

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Shifting cultivation practiced by ethnic people in CHTs seriously exposes soil through clearing and burning of jungles. Though shifting cultivation has many negative effects, we recorded little change at the slashing stage on soil physical and chemical properties. Shortening of the fallow period is followed by a reduction in biomass, nutrient depletion, and low productivity. The success of shifting cultivation depends on the length of the fallow period. The frequent return of farmers to the same land not only results in declining yields but also reduces biomass production per unit area. The length of the fallow period should not be less than 10 years to have productive shifting cultivation, and this is practically impossible under the existing socioeconomic conditions in CHTs, because the per capita land area is too low.

Knowledge Management: Journal