Faqrul Islam Chowdhury
Institute of Forestry and Environmental Sciences, University of Chittagong, Chattogram, Bangladesh;
Imon Barua
Institute of Forestry and Environmental Sciences, University of Chittagong, Chattogram, Bangladesh;
Aminul Islam Chowdhury
Department of Applied Chemistry and Chemical Engineering, University of Chittagong, Chattogram, Bangladesh;
Víctor Resco de Dios
School of Life Science and Engineering, Southwest University of Science and Technology, Mianyang, China
Mohammed Shafiul Alam
Institute of Forestry and Environmental Sciences, University of Chittagong, Chattogram, Bangladesh;
Soil physicochemical properties; Forest plantation; Land use; Soil organic carbon; Soil compaction
Kaptai Upazila, in the CHTs of Bangladesh
Farming System
Study area: The study was conducted at Wagga Union (22° 31015.2” N and 92°07'49.1” E), under Kaptai Upazila, in the CHTs of Bangladesh. CHTs show an undulating relief with hills running from NorthSouth, and with summits reaching 300 − 1,000 m above mean sea level. Slopes are generally above 40%, and they are often subject to landslides and soil erosion. Soils in the study area develop from semiconsolidated to consolidated shales, siltstones, and sandstones. The area has a tropical climate with heavy rainfall concentrated in the summer monsoon period (Feroz et al., 2014). The parent materials are low in weatherable minerals (Biswas et al., 2012). The area is known for its high-intensity slash-and-burn practiced on the steep slopes of the hills by the indigenous people (Suryatmojo, 2014). To protect this hilly area from further degradation, agroforestry and reforestation practices have been established in different parts of the CHTs. Experimental design As previously mentioned, we used sampled across three land use categories, agroforestry, forest plantations, and denuded hills. The sampling plots within the agroforestry and reforested land use types used to be under a slash-and-burn regime, and they were transformed into the current land use type about 10 years before experiment inception. The denuded hills ecosystem (slash-and-burn practice) at the time of sampling had been left fallow for 3 years after the last harvest. The slash-and-burn denuded hills were characterized by no vegetation while the plantation forest was dominated by Acacia auriculiformis and a scarce litter cover on the soil. Agroforestry plots had an intensive seasonal mixed cropping practice throughout the year, along with fruit trees such as Mangifera indica (Mango), Psidium spp. (Guava) and Carica spp. (Papaya). Agroforestry plots were treated mechanically during farming and harvesting seasons, and they were fertilized by cow manure. Four plots within each land use type were selected randomly from each of three different villages (i.e.,: Pagliupor, Paglimoddho, and Paglinichu) within Wagga Union. We collected samples at 0–15 cm depth in the middle of the slope using a soil auger (four samples per plot) and a soil core (four samples per plot). To avoid the interaction among the different land-use types, sampling points were taken at least 30 m inside the boundary of each landuse category. Hence, 96 soil samples (3 villages 4 plots 4 samples 2 soil sampling tools (auger and core)) were taken per land use type, adding up to 288 samples in total (96 3 land use types). Soil samples collected by auger were used for analyses of soil chemical properties (N, P, K, SOC, SOM and pH) and samples collected by soil core were used for measuring soil physical properties (soil MC, MBD, DBD and particle density). For soil texture measurements, one composite sample was analyzed by mixing the 48 soil samples (3 villages 4 plots 4 samples) within a land use. The soil samples were packed and labelled with airtight plastic bags for further laboratory analyses. In the laboratory, we sieved the samples for chemical analyses through a 10-mm wire mesh to remove gravel, small stones, and coarse roots, and then we passed the sample through a 2-mm sieve. We then stored the sieved samples at room temperature. Moist samples of soil were oven-dried at 105°C for 48 h. Determination of soil physical properties Soil texture was determined with the Bouyoucos hydrometer method (Miah et al., 2010). To determine soil PD, we used two cylinders marked every 10 mL. The first cylinder was filled with 10 mL of water and the second with 2 g of soil, which had been previously burned in a furnace and weighed (Sw). We poured the water from the first cylinder to the cylinder with burned soil until the water level reached the 10 mL mark and we calculated sample volume (Sv) as the water remaining in the first cylinder. Soil PD was then determined following (Mahmud et al., 2018).
Geology, Ecology, and Landscapes,
Journal