The Physical Soil Factors Affecting Crop Production

June 7, 2023June 27, 2023 Agric4Profits

Soil is the uppermost layer of the earth that supports the growth of higher plants, mainly by providing a medium for plant roots and supplying elements that are essential to the entire plant.

The soil is the regulator of water supplies in rivers, lakes, and underground aquifers; it recycles raw materials such as humus, and is a habitat for soil organisms, including beneficial organisms, predators, prey, producers, consumers, and parasites.

Soil type, fertility, and the present and potential systems of soil management have considerable influence on agricultural production. Regional variations in soil types often influence the prospect of growing particular crops in different parts of the country. Also, fertility level influences soil types and traditional soil management techniques used in their maintenance.

Physical Soil Factors Affecting Crop Production

These include the soil’s texture, structure, porosity, and bulk density.

1. Soil Texture

This is defined as the relative proportions of the sand, silt, clay, and gravel/stone particles (composition) in the soil. The proportion of solid soil particles provides a useful guide to a soil’s potential for agricultural crop production since it exerts a major influence on soil characteristics.

The soil texture influences the water-holding capacity (through the clay type and content and capillary conductivity), temperature, drainage, and nutrient retention capacity of the soil.

Also, soil texture influences the efficacy of soil-applied pre-emergence herbicides and other pesticides.

Soils are classified into light (sandy, workable), medium (loamy, most workable), or heavy types (clay, unworkable) based on soil texture, due to its close relationship to the workability (the ease of working the soil with machinery) of the soil.

2. Soil Structure

This is defined as the arrangement of the particles (sand, silt, clay) in the soil. It influences the soil tilth, root growth and development, gaseous exchange/aeration, drainage, water infiltration into the soil, and efficiency of water and nutrient uptake by plants (through capillary conductivity).

“Structural stability” is the ability of the soil to resist deformation when wet. It is influenced by the clay content, presence of lime, iron oxides, and humus. However, soil structure is not a stable soil property, and therefore changes with time and weather.

Poorly stable soil aggregates slake (collapse) easily while good aggregate structure maintains the shape when wet for a short time and gradually pieces off thereafter.

Good structural stability is essential to prevent soil degradation and limited crop growth. Soil structure can be improved by the addition of decomposable OM (e.g. farmyard manure, FYM), crop roots, and crop residues. Heavy machinery causes damage to soil structure in wet soil, especially heavy clay soils.

3. Soil Porosity

This is defined as the percentage volume filled with air when the soil is fully drained of saturated water.

The pore sizes include micropores (smallest pores containing only water which rarely dries out and is unavailable for crop uptake); mesopores (middle-sized pores containing water available to plants and which allow free aeration of the soil); and macropores (pores greater than 0.1 mm in diameter, can drain easily to allow in the air after full wetting of the soil).

Soil porosity influences the infiltration of water into the soil, water-holding capacity, drainage, and aeration of the soil aggregates; these properties have a significant influence on the SOM status.

Ecologically, soil aeration plays a significant role in organic residue decomposition; oxidation-reduction of elements, especially nutrients; plant growth; nutrient and water uptake; soil compaction; soil structure; and soil cultivation.

Aeration capacity is very high in sandy soils, optimal in loamy soils, and very low in clay soils. However, organic matter additions (which increase the number of meso- and macro-pores) can improve the aeration capacity of clay soils.

4. Soil Bulk Density

This is the mass of soil per unit volume of the soil. It is determined by the volume of pore spaces in the soil; the more the pore spaces, the lower the bulk density, and vice versa for high bulk density or soil compaction.

Soil bulk density affects the workability of the soil, especially concerning mechanical cultivation, and especially in dry weather. No-tillage or minimum tillage is also strongly affected by soil compaction.

5. Soil Water

Water is held in the soil in three forms, namely:

1. Capillary water (the water held by surface tension forces as a continuous film around the particles and in the capillary pore spaces of the soil);

2. Gravitational water (the water held to the soil particles against gravitational forces and suction force of the roots, and which drains under the influence of gravity); and

3. Hygroscopic water (water adsorbed from an atmosphere of water vapor as a result of attractive forces on the surface of the soil particles and aggregates).

Soil water is very critical to root absorption of essential nutrients from the soil, soil temperature, microbial and microbial soil activities, organic matter decomposition, etc. The farm soil needs to be at field capacity always to ensure optimal growth and development.