3.1-3.4: Soil Composition, Agriculture Type & Yield Notes:

SOIL COMPOSITION

Definition:  

• Soil is the loose outer layer beneath Earth’s surface i.e. the essential medium for plant growth. It’s made up of four main components:

Typical composition of soil:

• 40–45% inorganic matter

• 5% organic matter

• 25% water

• 25% air

Proportion of the composition relies on:

1. Size of mineral particles

2. Type of soil

3. Weather conditions

Soil Classification:

• Soil can be classified into:

  1. Clay

  2. Silt

  3. Sand

Soils for Plant Growth:

Soil as a Medium for Plant Growth:

• Provides anchorage for roots.

• Supplies water, air, and mineral ions.

• Contains organic matter for nutrient recycling.

Organic Matter:

They are decomposers that produce humus. They include:

1. Earthworms: 

   • Mix and aerate soil → improve air and water movement.

   • Spread and break down organic matter → form humus.

   • Their tunnels help root penetration.

2. Bacteria:

   • Decompose dead material → release nutrients.

   • Converts waste to simple chemicals.

   • Convert nitrogen compounds (nitrification) and important in nitrogen cycle.

   • Maintain soil fertility.

3. Fungi:

   • Feed directly on dead matter

   • Decompose complex organic matter (cellulose, lignin).

   • Form mycorrhizae → help roots absorb water and minerals.

   • Bind soil particles → improve structure.

High Levels of Organic Matter

• Increase nutrient availability (especially nitrogen and phosphorus).

• Improve soil structure → better aeration and drainage.

• Enhance water‑holding capacity.

• Support microbial activity → faster nutrient recycling.

• Reduce erosion by binding particles together.

Soil pH

• Depends on:

  1. Parent rock type (limestone → alkaline; granite → acidic).

  2. Rainfall (heavy rain → leaching → acidity).

  3. Organic matter decomposition (produces acids).

  4. Fertilizer use (ammonium‑based → lowers pH).

• Affects:

  1. Nutrient availability: certain ions become insoluble in acidic soils.

  2. Microbial activity: bacteria prefer neutral pH (≈ 6–7).

  3. Plant growth: each species has an optimal pH range.

  4. Soil structure: extreme pH can damage aggregates.

• Farmers try to change the pH by adding acidifiers or fertilizers.

Differences Between Sandy and Clay Soils:

Types of Agriculture:

• Ease of cultivation: how easily the soil can be ploughed.

• Drainage: capacity of the soil to drain water without getting water loss.

Techniques Used to Increase Agricultural Yields

Crop Rotation

• Growing the same crop repeatedly depletes specific nutrients.

• Rotation alternates crops that use different nutrients or restore them.

• Nitrogen‑fixing crops (e.g. clover, peas, beans, alfalfa) add nitrogen to soil via root nodules containing bacteria.

• These crops belong to the legume family and enrich soil for the next planting.

• Leafy crops (e.g. cabbage, spinach) use nitrogen heavily → best grown after legumes.

• Deep‑rooted crops (e.g. potatoes) alternate with shallow‑rooted crops to improve soil structure.

• Advantages:

  • Reduces pest and disease buildup by breaking life cycles.

  • Provides fodder for livestock (e.g. clover grazed by cattle).

  • Saves money by reducing need for chemical pesticides.

  • Maintains fertility and increases yield.

Fertilizers

Eutrophication happens when fertilizers are washed off from the land by rainwater into lakes and rivers (can lead to lifeless bodies of water).

Irrigation:

Definition: supplying water artificially to crops when rainfall is insufficient.

Controlling Pests and Diseases

• Pests and diseases reduce yield and quality.

• They destroy leaves, roots, and fruits.

• Cause economic loss and food shortages.

• Control maintains healthy crops and stable food supply.

• Methods:

Why Weeds Should Be Controlled

• Compete with crops for light, water, space, and nutrients.

• Reduce yield and quality.

• Make harvesting difficult.

• Provide shelter for pests and diseases.

• Increase labor and cost of cultivation.

Advantages of Herbicides

• Efficiency: kill large areas of weeds quickly and uniformly.

• Selectivity: some herbicides target specific weeds without harming crops.

• Labor saving: reduces need for manual weeding.

• Improved yield: crops get more nutrients, light, and space.

• Ease of use: simple to apply with sprayers or machinery.

Disadvantages of Herbicides

• Overuse pollutes soil and water.

• Can harm non‑target plants and wildlife.

• Weeds may develop resistance.

• Chemical residues may affect human health.

Alternatives of Using Herbicides

Crop Diseases

Causes

• Fungi, bacteria, viruses, and nutrient deficiencies.

• Spread by wind, water, insects, or contaminated tools.

Effects

• Wilting, rotting, stunted growth, poor yield.

• Economic losses and food scarcity.

Control

• Fungicides: Prevent fungal infections.

• Resistant varieties: Genetically bred to resist disease.

• Crop rotation: Reduces buildup of pathogens.

• Sanitation: Remove infected plants and clean equipment.

• Controlled environments: Greenhouses reduce exposure to pathogens.

Selective Breeding of Animals and Plants

• Farmers increase productivity by selectively breeding animals or plants with desirable traits.

• Breeding can occur within or across species to improve yields.

• It can be done in laboratories for faster results than natural breeding.

• Genes can be transferred from one plant to another, or even between plants, animals, and microorganisms.

• Example: if a wild grass has a gene for herbicide resistance, that gene can be inserted into a crop like wheat.

• This allows herbicides to kill weeds without harming the crop.

• About 85 % of maize grown worldwide is genetically modified to resist the herbicide glyphosate.

Genetically Modified Organisms (GMOs)

• Genetic modification involves introducing genes from one organism into another to give useful traits.

• Example: transferring a herbicide‑resistant gene from wild grass into wheat.

• The result is a crop that survives herbicide spraying while weeds die.

• 85 % of maize grown globally is genetically modified to resist glyphosate.

• GM technology allows faster improvement of crops compared to traditional breeding.

Controlling Growing Environments

• Productivity increases when plants and animals are removed from natural conditions and grown in controlled artificial environments.

• Farmers control light, heat, water, and food availability.

• Greenhouses are examples. They are used in the Netherlands to grow peppers under constant light, shortening the growing season by four weeks.

• Pumping extra CO₂ into greenhouses speeds up photosynthesis, increasing sugar production, improving flavour, and boosting yield.

• Hydroponics involves immersing plant roots in a nutrient solution inside a greenhouse.

• No soil → fewer pests and weeds → less pesticide use.

• Enables high yields at reduced cost.

• Battery‑cage systems house large numbers of egg‑laying hens in confined spaces.

• Controlled feeding and lighting increase egg production.

• These systems face animal‑welfare opposition for limiting movement and compassion in farming.

NOTES DONE BY FARIDA SABET

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