The study area of this research work comprises the western boundary of the Rajshahi University campus, Rajshahi city of Bangladesh ( Figure 1 ). This area is situated in the central-western part of Bangladesh. For getting the soil profile of Rajshahi University campus area, two separate digging sites were selected. One of the profile sites is located in the latitude 24.37363 N and longitude 88.629888 E, another one is located in the latitude 24.373885 N and longitude 88.629568 E.

The Bengal Basin, which spans a considerable area in Bangladesh, is an intricate sedimentary basin located between the Peninsular Indian Shield and the Shillong massif. It is located near the triple junctions of the Indian and Eurasian plates and the Burmese sub-plate. It contains the thickest sedimentary piles (>20 km) in the

world. Tectonically, the Rajshahi Division belongs to the Southern slope of Rangpur Saddle or Bogura Shelf and its sedimentary cover is about 700 m, while the thickness gradually increases in the southern part of the platform ( Reimann, 1993 ; Hossain et al., 2009 ). The Ganges-Brahmaputra-Meghna River system carries these sediments primarily. Because of the elevation change, the Ganges River flows from downstream to the south in the basin, according to a grain size analysis of the river bed sediments.

The soil is the thin topmost layer of the earth’s crust mainly composed of organic matters, minerals and rock particles that support life. A soil profile is a vertical cross-section of the soil, made of layers running parallel to the surface. These layers are also known as soil horizons. The top layer is generally fertile, with sandy clay or sandy loam and silty textures, which makes it suitable for agriculture. The soil is moderately rich in organic matter due to crop residues and the natural vegetation of the area. Below the topsoil, the subsoil layer of the studied profiles is typically loamy sand or medium sand in nature. It can sometimes become less compacted, having some root penetration. Lower layer of the profiles consists of weathered alluvial deposits, mainly derived from the sediments of the Ganges River. Main texture is slightly mixed sandy loam or loamy sand or medium loam, sandy clay loam, comparatively moist, locally oxidized spotted with light brown color or dark spot, slightly sticky when wet. The characteristics of soil profile-1 (SP1) are shown in Table 1 and Figure 2 .

The characteristics of soil profile-2 (SP2) are shown in Table 2 and Figure 3 .

Analysis of the subgrade soil enables us to identify it as falling into classes S2and S4 on the basis of their CBR of between 6 and 26 ( CEBTP, 1984 ).

The particle size classes are based on the particle size grades of the British Standards Institution and the Massachusetts Institute of Technology and the measured particle size data are shown in Table 3 . Particle size data of a soil profile is very important for delineating the soil characteristics of a crop land. In the present study, two representative soil profiles have been dug near the western boundary of the Rajshahi University campus to know the soil characteristics of the experimental crop land of the Institute of Environmental Sciences (IES), University of Rajshahi. According to size grade, sand particles are divided into coarse sand, medium sand, fine sand, very fine sand. In this case, overall profile samples show coarse sand (0.24 - 1.47 wt%), medium sand (8.51 - 23.98wt%), fine sand (11.26 - 30.26 wt%), very fine sand (17.14 - 44.12 wt%). On the other hand, silt (8.82 - 33.84 wt%) and clay (5.19 - 27.02 wt%) are comparatively identical. Overall, sands (55.05 - 82.30 wt%) are dominant particle size in both profiles.

The soil texture triangle and the ratios of sand, silt, and clay of two soil profiles SP1 and SP2 are shown in Table 4 . We can learn about characteristics like permeability and water-holding capacity by understanding the texture of the soil. These attributes affect the kinds of plants that can grow there as well as the rates of erosion. Applications for using soil texture analysis include construction, agriculture, and conservation. This texture also influences the key characteristics such as drainage, water storage, workability, susceptibility to soil erosion and suitability for different uses. It also plays a major part in defining soil structure.

The texture class of a soil is defined on the relative proportions of sand, silt and clay. The relative amounts of clay, silt, and sand particles in the soil allow for the classification of mineral soils into 11 major classes ( Figure 4 ).

Soil profile 2 (SP2) shows mostly sandy loam texture all over the profile length. However, soil profile 1 (SP1) has slightly heterogenous. It shows medium loam, sandy loam, sandy clay loam and loamy sand.

All over the profile 2 consists of individual grains, which can be seen and felt. In dry condition, clods are easily break. During digging or wet condition (with moisture), soils were moderately gritty to gritty; forms ball and did not show ribbons or very poorly visible.

There are various levels in soil taxonomy, such as great group, subgroup, family, order, and suborder ( Donovan, 1981 ). Soil order is the broadest classification level in the USDA (United States Department of Agriculture) Soil Taxonomy system. This system of classification primarily makes use of the quantitatively measured characteristics of the soil, such as its organic matter content, base saturation, texture, structure, moisture content, temperature, cation exchange capacity, and clay mineralogy ( Banglapedia, 2021 ).

Based on a number of criteria, including parent materials, soil formation (the percentage of soil profile development), weathering (chemical and physical), and climate, the earth’s soils are divided into several classes.

There are twelve different types of soil in the world: Mollisols, Alfisols, Entisols, Inceptisols, Vertisols, Spodosols, Ultisols, Oxisols, Histosols, Andisols, and Gelisols. Within this international group, Bangladesh is exposed to six of these types: Entisols, Inceptisols, Mollisols, Alfisols, Ultisols, and Histosols.

In these six types, the study area is prominently rich with Entisols. As the soil profiles of the studied bore logs show very weak development beyond the A-horizon and lack clear diagnostic horizons, they are almost unaltered sediments. This soil is dominantly sandy loam means sandy mineral-rich soil and comparatively low in organic matter, natural fertility and water holding capacity ( Weil & Brady, 2016 ). Near the Ganges River system, the floodplain soil is more fertile due to the regular deposition of silt from flooding, which replenishes nutrients and enhances agricultural productivity. We also know very well that there are Entisols covering about sixteen percent of the Earth’s land area that is free of ice. These occur where the rate of erosion or deposition is higher than the rate of soil formation, such as in dunes, steep slopes, and flood plains, or in areas that have recently been exposed to parent materials. Soil series depends on the geographical location of soil. Ten soil series under Alfisols are reported in Southeastern Missouri ( Aide, 2024 ).