Burning Effects on Soil Properties in Upland Watershed of Bangladesh

Burning Effects on Soil Properties in Upland Watershed of Bangladesh *Md. Monzer Hossain Sarker **Tamanna Hossen ***Md. Mustainur Rahman Abstract A study was conducted to investigate the effects of burning practices on the physico- chemical properties of forest soil in the upland watershed in Chittagong. The study conducted at the adjacent hills of Chittagong University campus showed that at 0-5 cm soil depth burning increased moisture, field capacity and maximum water holding capacity and decreased bulk density of soil. Burning decreased organic matter and increased pH at all soil depths (0 - 5, 5 - 15 and 15 - 40 cm). Soil moisture, field capacity, maximum water holding capacity and bulk density of burnt forest land were 2.94%, 28.08%, 39.44% and 1.63 gcm-3, while their corresponding values in no burnt forest land were 1.54%, 22.01%, 34.20% and 1.70 gcm-3. In 0 – 5 cm soil depth organic matter, soil pH (1:2 H2O) and potential soil pH (1: 2 KCl) were 0.90%, 6.36 and 6.16, while their corresponding values in no burnt forest land were 1.89%, 5.23, and 5.10. Keywords: Burnt, Physiology, Forest, Jhums, Field capacity and soil properties Introduction In Bangladesh, through human activities, burning occurs in forest lands in different ways. In shifting cultivation, burning is an important and common method in preparation of land in Chittagong and Chittagong Hill Tracts (CHTs). Burning is a silvicultural system that is used to reduce understory growth, eradicate invasive species and create clear-open stands (Hamman et al., 2008; Wade and Lundsford, 1990). All the remaining vegetation on land consisting of small trees, shrubs and herbs are cut, dried and burnt sequentially to prepare the land for planting seedlings. In hilly region slashing and burning has also been chosen as a common, easier and cheaper method for land preparation before planting. Besides, occur- rence of both incendiary and accidental fires is common in the evergreen and *Department of Environmental Science and Disaster Management, Noakhali Science and Technol- ogy University, Noakhali, Bangladesh **Department of Environmental Science, Stamford University, Bangladesh ***Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong, Bangladesh Green University Review of Social Sciences, Volume 04, Issue 01, June-2018 semi-evergreen forests of Chittagong and CHTs in the dry season, especially during December to March. Some insignificant surface fires spread into the bamboo forests from the ‘jhum’ (a traditional slash-and-burn cultivation system practiced by the ethnic groups in the Chittagong and CHTs) in the Un-classed State Forests along the boundaries of the forest reserves, but when the affected area is a teak plantation, it may occasionally be ‘crown fire’ as well. It brings temporal to complete change in soil and climate, and the changes become even greater. Burning reduces content and depth of organic matter, and decreases total nutrient pool of forest floor (Rosoman 1994; Certini 2005). Fire damaged trees are infected by pathogens and attacked by insects in later growth stages. In the fire-affected plantation, seedlings like Dipterocarpus spp. (garjan), Gmelina arborea (gamar) and Syzygium fruticans (dhakijam) could not recover from the injury. T. grandis (teak) seedling, however, recover fairly well after burning since this is a fire resistant species. No further information is available in Bangladesh on the effects of fire, although many studies available on various aspects of environment in other countries (Andreas et al. 2007; Philon 1998; Becker 1995). In these studies, fire effects reported on various aspects of environment were physical, chemical and biological properties of soil; germination of seeds, regenera- tion, mortality morphology, physiology, etc. of plants; wildlife injury, mortality, food, aquatic fauna, bird; stream flow and many other aspects of environment (Andreas et al. 2007). Forest fire has mostly detrimental effects on various aspects of environment including soil. This alters physical, chemical and biological properties of soil. Forest fires cause immediate changes in vegetation as well as complete elimination of some species and accelerate others to grow. The most damaging aspect of forest fire is the destruction of bio-diversity including both plants and animals with the addition of CO2 in the atmosphere, one of the most powerful greenhouse gases. Haque et al. 2012; Haque et al. 2014; etc. reported clear-felling and burning effects on soil biological properties in the CHTs. Getting impression from these two studies, this research aimed to determine the effects of burning on soil physical and chemical properties. Methodology Study Area Selection and Soil Sampling The Chittagong University Campus lies between about 22°27'30" and 22°29'0" North latitudes and 91°46'30" and 91°47'45" East longitudes (Banglapedia, 2013), located at Fatepur, a union under Hathazari Thana of Chittagong District. Hilly land within the Chittagong University campus is brought under forest through plantations during the last three decades. On the other hand, people from nearby villages used to cultivate hills outside campus from long before generation 180 | Page Burning Eects on Soil Properties in Upland Watershed of Bangladesh to generation. Therefore, to investigate the effects of forest burning on soil properties, burnt land (BL) was selected from the hilly area in the west side of the Universi- ty campus whereas forest lands i.e. no burnt land (NBL) were selected beside the botanical garden of Chittagong University. Farmers are practicing cultivation on the hilly land after clearing the forest vegetation consisting of thickets, bamboos and grasses of the past time. In the burnt area all the vegetation of the land were slashed in December- January and after drying burnt in mid February - March, i.e. in pre-monsoon time. Thus, no tree was present in the burning area except some thickets and grasses. On the other hand, the vegetation in no burnt area was highly disturbed due to biotic interference such as human interference, grazing etc. The land contained secondary vegetation such as thickets, some scattered trees, thatch- ing grasses and some bamboos. Soil samples were collected from both burnt no burnt forest situated side by side on similar topography on the mid February 2015 during the pre monsoon. For each land use, 3 replicated soil samples were collected from a depth of 0 - 5 cm, 5-15 cm and 15 - 40 cm digging mini soil profiles. Soil of each depth of three replicates of a land cover were mixed together to make a composite sample and placed in labeled, air-tight plastic bags and carried to the laboratory and analyzed for soil chemical properties. Soil physical properties such as soil moisture, field capacity and bulk density were determined from core samples collected separately from the upper soil layer for each land use at each paired site. Soil Analysis In the laboratory, moisture content, maximum water holding capacity and field capacity were determined from core samples collected for bulk density. 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 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 water reached the 10 ml mark. The remaining water in the first cylinder indicated 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. 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). 181 | Page Green University Review of Social Sciences, Volume 04, Issue 01, June-2018 Results Soil Profile Description BL: 0-5 cm: 5YR6/4, light reddish brown; sandy loam; medium to very coarse sub-angular blocky; very fine to fine roots; moderately well drained; clear wavy boundary 5-15 cm: 7.5YR5/4, brown; sandy loam; medium to very coarse sub-angular blocky; moderately well drained; clear wavy boundary 15-40 cm: 7.5YR6/3, light brown; sandy loam; medium to very coarse sub-angular blocky; moderately well drained NBL: 0-5 cm: 5 YR8/2, pinkish white; loamy sand; week to moderate medium to very coarse sub-angular blocky; common fine to medium roots; moderately well drained; clear wavy boundary 5-15 cm: 5YR7/3, pink; loamy sand; week to moderate medium to very coarse sub-angular blocky; few fine to medium roots; moderately well drained; clear wavy boundary 15-40 cm: 5YR7/3, pink; loamy sand; week to moderate medium to very coarse sub-angular blocky; few fine to medium roots; moderately well drained Soil texture: Soil texture in burnt forest land was sandy loam and no burnt land loamy sand (Table 1). Both the soils were coarse textured and inherently almost similar, which justified that to see the effects of burning on pair land. Table 1: Soil texture at 0 -5 cm soil depth in burnt and no burnt forest land in Chittagong Land condition Sand (%) Silt (%) Clay (%) Texture BL 69.80 28.60 1.60 Sandy loam NBL 80.40 18.00 1.60 Loamy sand Soil Physical Properties Physical properties such as soil moisture, field capacity and maximum water holding capacity were higher and bulk density was lower in burnt forest land compared to no burnt forest land (Table 2).

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