Influence of Land-Use Systems and Topographic Variables on Soil Physical Indicators in the Chittagong Hills, Bangladesh.

Abstract

This study evaluates the influence of land-use systems and topographic variables on soil physical indicators in the Chittagong Hills, Bangladesh. A total of 81 topsoil samples (0 - 20 cm depth) were collected from nine land-use types, spanning altitudes from 26.43 m to 106.35 m and slope lines from 26.07% to 77.30%. Soil structure varied from blocky to granular, and soil textures ranged from sandy loam to sandy clay loam, with color ranging from dark grayishbrown to reddish-brown, exhibiting significant variation across land-use sites. One-way analysis of variance (ANOVA) results revealed significant differences (p < 0.05 to p < 0.001) in soil physical indicators across land-use practices. Moisture-related indicators such as moisture content (MC), field capacity (FC), maximum water holding capacity (MWHC), total porosity, and soil organic matter (SOM) were highest in natural forest and agroforestry systems compared to acacia forest, young teak forest, mature teak forest, and shifting cultivation. Dry and moist bulk density (DBD and MBD) were highest in the acacia forest, teak forest, and shifting cultivation site. Pearson correlation analysis confirmed strong positive relationships between slope, altitude, sand content, bulk density (BD), but negative correlations with FC, MWHC, total porosity (TP), silt, SOM (p < 0.01). Among soil physical indicators, strong positive correlations were observed between sand content, DBD, and MBD, while strong negative correlations were observed between silt content, MC, FC, MWHC, TP, and SOM. Regression analyses indicated significant negative relationships of FC and SOM with altitude and slope, whereas MWHC was negatively associated with altitude only. Sand content showed significant positive relationships with both topographic variables, while dry and moist bulk density were positively associated with slope only. The study concludes that variations in the land-use practices along altitude and slope gradients drive the soil physical indicators and soil OM, with steeper slopes showing compacted, coarser soils and lower SOM. Such findings emphasize the role of natural forests and agroforestry systems in preserving soil physical health, whereas shifting cultivation and monoculture plantations lead to soil degradation. Considering climate change variables, future research should focus on the effects of temperature and rainfall on soil physical properties and SOM to conserve the forest ecosystems.