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Soil Properties Under Different Vegetation Types in Chittagong University Campus, Bangladesh

Md. Akhtaruzzaman*
Department of Soil Science, University of Chittagong, Chittagong-4331, Bangladesh

Sajal Roy
Department of Soil Science, University of Chittagong, Chittagong-4331, Bangladesh

Muhammad Sher Mahmud
Department of Soil Science, University of Chittagong, Chittagong-4331, Bangladesh

T. Shormin
Department of Soil Science, University of Chittagong, Chittagong-4331, Bangladesh

Abstract/ Executive Summary:

Soil physical and chemical properties at three layers such as top (0-10 cm), middle (10-20 cm) and bottom (20-30 cm) layers under three different vegetation types were studied. Soil samples were collected from Acacia forest, vegetable and fallow lands of Chittagong university campus, Chittagong, Bangladesh. Results showed that sand was the dominant soil particle followed by clay and silt fractions in all soil depths under different vegetation types. Soils of fallow land showed the highest values of bulk density while forest soils had the lowest values at three depths. Acacia forest soil having lowest values of dispersion ratio (DR) is less vulnerable while fallow soil with highest DR values is more vulnerable to soil erosion. The lower pH value at all soil layers in three ecosystems represented that soils under study are acidic in nature. Contents of organic matter, total nitrogen, exchangeable cations (Ca2+, Mg2+, K+ and Na+ ) and cation exchange capacity (CEC) were observed higher in Acacia forest soils compared to vegetable and fallow soils. Only soils of vegetable land had higher level of available phosphorus in three layers than that of other two land covers. The study also revealed that different soil properties were observed in three different vegetation types might be due to variation in vegetation and agronomic practices.

Keywords: Vegetation types, Physical properties, Dispersion ratio, Chemical properties

Location: Chittagong university campus, Chittagong, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Physico-Chemical

Objectives:

The objective of the present study is to assess some physical and chemical properties of soil under different land vegetation. This study provides information that can be useful for selecting better ways to improve soil productivity in the investigated area.

Methodology:

Study area: The study was conducted in different sites under three vegetation covers at the campus of Chittagong University, Hathazari, Bangladesh . Geographically, the studied area of Chittagong University extends between 22°30′ to 22°47′N latitude and 91°58′ to 91°79′E longitude. The soils under present study are classified as Brown Hill Soils as general soil type. Topographical features were maintained more or less similar during soil collection. The general information on three locations was given in Table 1. Chittagong region has a sub-tropical climate and is characterized by long summer and short winter. Mean annual precipitation ranges from 2877 to 3842 mm and mean annual temperature varies from 25.5° and 25.7°C. The present study was carried out in the area with three different vegetation types under Acacia forest, vegetable and fallow lands. In Acacia forest of the studied area, the vegetation is composed of akashmoni (Acacia auriculiformis) as the major species while mangium (Acacia mangium), gamar (Gmelina arborea), chapalish (Artocarpus chaplasha) etc. as minor tree species. In the vegetable land, major winter vegetables are cabbage (Brassica oleracea var capitata), cauliflower (Brassica oleracea var botrytis), hyacinth bean (Lablab niger) tomato (Lycopersicon esculentum), radish (Raphanus sativus), brinjal (Solanum melongena), bottle gourd (Lagenaria siceraria), red amaranth (Amaranthus gangeticus), while summer vegetables such as pumpkin (Cucurbita maxima), jinga (Luffa acutangula), bitter gourd (Momordica charantia), ribbed gourd (Luffa acutangula), teasle gourd (Momordica cochinchinensis), ladies finger (Abelmoschus esculentus), Indian spinach (Basella alba) etc. are grown. Agricultural practices such as tillage, irrigation and fertilization are also followed by the local farmers. Organic manures and chemical fertilizers are usually used in the vegetable field during growing seasons. The fallow land is dominated by grasses. Herbs like assamlata (Mikania micrantha), assam gas (Grewia nervosa) and shrubs such as lajjabati (Mimosa pudica), bon tejpata (Melastoma malabathricum) etc. are also frequent. Livestock were also found grazing in fallow land during soil collection. Sampling method and analysis Three plots of 10×10 m size were selected for soils under each vegetation type. Soil samples were collected in winter and summer seasons. Soils were taken from top (0-10 cm), middle (10-20 cm) and bottom (20-30 cm) layers at four sites of each plot for analysis. Three replications for single depth were followed during soil collection. Prior to laboratory analysis, the soil samples were air-dried at room temperature, crushed and passed through a 2 mm diameter sieve. Particle size distribution of the soils was determined by hydrometer method (Day 1965). Bulk density was measured using the procedure described by Blake (1965). The dispersion ratio (DR) was determined as a measure for structure stability. According to Middleton (1930), DR is calculated using the following equation: DR = (c/d) × 100, where c is the percentage of water-dispersible silt-plus-clay determined by the pipette method when 20 g of air-dried soils was agitated end over end 20 times without dispersion agent with 1 L of distilled water in a sedimentation cylinder and d is actual silt-plus-clay amount determined by routine particle-size distribution analyses with Na-hexametaphosphate (Calgon) as a dispersing agent. Based on the criteria proposed by Middleton (1930), soils having a dispersion ratio?15.0 are nonerosive, and soils having a dispersion ratio?15.0 are erosive. Cation exchange capacity (CEC) was determined after extraction of the cations with ammonium acetate (Black 1965). Soil pH was measured in soil-water suspension (1:2.5) using a corning glass electrode pH-meter. Organic carbon was determined by wet-oxidation method of Walkley-Black (1934) and the percentage of soil organic matter was calculated by multiplying value of organic carbon with 1.724, the Van Bemmelen factor (Piper 1950). Total nitrogen of soil was measured by micro-Kjeldahl method (Jackson 1973). Exchangeable calcium and magnesium were determined by EDTA method while ex-changeable potassium and sodium were determined using a flame photometer (Jackson 1973). Available phosphorus was extracted with Bray and Kurtz no.2 extractant and measured by SnCl2 reduced molybdophosphoric blue color method using spectrophotometer (Jackson 1973). Significance of difference in soil properties in different land uses was tested by paired t test using Minitab (1996).

Source of Information: Journal of Forest and Environmental Science, Vol. 36, No. 2, pp. 133-142, June, 2020

Article Link (Online Journal): https://doi.org/10.7747/JFES.2020.36.2.133

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study showed that Soils under study had poor physical and chemical properties in terms of proper production of forests or vegetable crops. Fallow soils with higher values of dispersion ratio represent more vulnerable to soil erosion compared to forest and vegetable soils. Soils under Acacia forest land had relatively higher content of organic matter, total nitrogen, exchangeable cations and CEC in comparison to vegetable and fallow sites. On the other hand, soils of vegetable land contained only higher amount of available phosphorus than that of other two land use types. There is a need for greater attention to improve soil characteristics. In vegetable land, proper agricultural practices should be followed to restore soil physical and chemical properties. Plantation or cultivation with suitable agricultural practices may be considered to minimize soil organic matter and nutrient loss from soil of fallow land. Further study is necessary to take proper measures to improve soil productivity and soil quality in area under study

Knowledge Management: Journal