Texture often changes with depth so roots have to cope with different conditions as they penetrate the soil. A soil can be classified according to the way the texture changes with depth. texture-contrast—abrupt texture change between the topsoil and subsoil. gradational—texture gradually increases down the soil profile …

The depth of a soil is measured by how far below the surface plant roots can extend before being stopped by barriers, such as rock, sand, gravel, heavy clay, compacted dirt, or cement. Below the topsoil (usually only a few inches deep) lies another layer called subsoil.

The effective depth of a soil for plant growth is the vertical distance into the soil from the surface to a layer that essentially stops the downward growth of plant roots. The barrier layer may be rock, sand, gravel, heavy clay, or a cemented layer (e.g. caliche).

Soil and Management Factors Influence Seeding Depth

• By Mahdi Al-Kaisi, Department of Agronomy.
• Soil texture and tillage influence available soil moisture.
• Soil texture and tillage affect seeding depth.

Soils used for mineralogy and weathering studies were studied the deepest, having an average depth of 127 cm (range: 5–2000 cm). Studies that used infrared spectroscopy analyzed soils between 5 and 150 cm (average: 31 cm). The average depth for soils analyzed for soil carbon was 23 cm, but ranged from 2 to 560 cm.

The five factors are: 1) parent material, 2) relief or topography, 3) organisms (including humans), 4) climate, and 5) time. If a single parent material is exposed to different climates then a different soil individual will form.

The amount, intensity, timing, and kind of precipitation influence soil formation. Seasonal and daily changes in temperature affect moisture effectiveness, biological activity, rates of chemical reactions, and kinds of vegetation. Topography. Slope and aspect affect the moisture and temperature of soil.

Scientists attribute soil formation to the following factors: Parent material, climate, biota (organisms), topography and time.

Soils are formed through the interaction of five major factors: time, climate, parent material, topography and relief, and organisms. The relative influence of each factor varies from place to place, but the combination of all five factors normally determines the kind of soil developing in any given place.

The relief features, parent material, climate, vegetation, and other life-forms, as well as time apart from human activities, are the major factors responsible for the formation of soil. 2. Climate: It is one of the important factors in the formation of soil because it affects the rate of weathering of the parent rock.

(i) Relief, parent rock or bedrock, climate, vegetation and other forms of life and time are important factors in the formation of soil. (ii) Various forces of nature such as change in temperature, actions of running water, wind and glaciers, activities of decomposers, etc. contribute to the formation of soil.

Four basic processes occur in soils— additions, losses, transformations (changes), and translocation (movement).

Soil minerals form the basis of soil. They are produced from rocks (parent material) through the processes of weathering and natural erosion. Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material.

Translocations: Movement of soil constituents (organic or mineral) within the profile and/or between horizons. Over time, this process is one of the more visibly noticeable as alterations in color, texture, and structure become apparent.

THE FIRST STEP IN SOIL FORMATION IS THE WEATHERING. SOILS THAT USUALLY DEVELOP FASTER AND FLATTER. PLANTS AND ANIMALS. LOTS OF PLANTS AND ANIMALS THAT DEVELOP SLOW SOIL TRENDS.

All soils consist mainly of two kinds of material: particles of minerals and rocks, and organic matter. Organic matter is any matter that is or once was living.

The following properties contribute to soil fertility in most situations:

• Sufficient soil depth for adequate root growth and water retention;
• Good internal drainage, allowing sufficient aeration for optimal root growth (although some plants, such as rice, tolerate waterlogging);

Water-holding capacity is controlled primarily by soil texture and organic matter. Soils with smaller particles (silt and clay) have a larger surface area than those with larger sand particles, and a large surface area allows a soil to hold more water.

Silt is smaller than sand but larger than clay. Medium textured soils (fine sandy loam, silt loam and silty clay loam) have the highest available water capacity, while coarse soils (sand, loamy sand and sandy loam) have the lowest available water capacity.

Sandy soil

• The water holding capacity of a soil is a very important agronomic characteristic.
• The water holding capacity is highest in clayey soil because it is made up of very small tightly packed particles that do not allow water to percolate.
• Hence The water holding capacity is the highest in Clayey soil.

sandy soil

A horizon

There are five soil horizons: O, A, E, B, and C. (R is used to denote bedrock.) There is no set order for these horizons within a soil. Some soil profiles have an A-C combination, some have an O-E-B, an O-A-B, or just an O.

Topsoil

Soils are named and classified based on their horizons. The soil profile has four distinct layers: 1) O horizon; 2) A horizon; 3) B horizon, or subsoil; and 4) C horizon, or soil base (Figure 31.2. 2). The O horizon has freshly decomposing organic matter—humus—at its surface, with decomposed vegetation at its base.

In short, when top layer of soil is exposed, it results in soil erosion and infertile soil.

5 to 10 inches

FOUR LAYERS

Soils can be very shallow (less than 25 cm), shallow (25 cm-50 cm), moderately deep (50 cm-90 cm), deep (90cm-150 cm) and very deep (more than 150 cm).

Solution : Temperature and rainfall are the two main climatic factors responsible for soil formation.

Following are the factors of soil formation:

• Parent Rock: The parent rock determines the colour, texture, permeability, chemical property and mineral content of the soil.
• Climate: Temperature and rainfall influence the rate of weathering.
• Relief: Altitude and slope determine the accumulation of soil at a place.

No. Soil formation is responsible for the number of factors. Weathering is the first and prime important for soil formation. Then the colonisation of bacteria, lichen, mosses, and sheltering of other organisms in the soil help in formation of humus.

Soil texture is not a factor which is responsible for the soil formation. Parent material (minerals and nutrients), Time, Climate, Relief and Organisms are the factors which are responsible for the soil formation.

Answer: D. Building embankment is the right answer.

And men are constantly cutting down trees, thus leaving the land barren and open for soil erosion. Humans are responsible because for their own benefit they are cutting tress and building plants and buildings, . The roots of trees holds the soil and prevent it in getting eroded in rainy season.

List out three methods of soil conservation

• Following methods are normally adopted for conserving soil:
• Afforestation:
• Checking Overgrazing:
• Constructing Dams:
• Changing Agricultural Practices:
• (i) Crop Rotation:
• (ii) Strip Cropping:
• (iii) Use of Early Maturing Varieties:

Overgrazing

Explanation: The top most part of the soil is fit for vegetation which is the top soil where humus is present which help the crops to grow properly.

They cover the plateaus of Maharashtra, Saurashtra, Malwa, Madhya Pradesh, Chhattisgarh and extend in South-East direction along Godavari and Krishna valleys. These soils contain essential clay minerals as montmorillonite.

loamy soil

Porous loamy soils are the richest of all, laced with organic matter which retains water and provides the nutrients needed by crops. Sand and clay soils tend to have less organic matter and have drainage problems: sand is very porous and clay is impermeable.

Generally speaking, clay-rich soils have the largest pore space, hence the greatest total water holding capacity. However, total water holding capacity does not describe how much water is available to plants, or how freely water drains in soil.

The topsoil layer is a mixture of sand, silt, clay and broken down organic matter, called humus. Humus is rich, highly decomposed organic matter mostly made from dead plants, crunched-up leaves, dead insects and twigs. The topsoil is relatively thin but it has most of the soil’s nutrients.