Soil Composition and Components

The Soil

• Soil is crucial for plant growth

Soil Composition

• Mineral particles are rock fragments combined with inorganic substances
  • They are formed through physical, chemical, and biological weathering of parent rock
• Organic content is a mix of living plants, animals, microorganisms, and their dead remains
• Air is held within pore spaces between mineral particles and organic content
  • Air enters the soil through diffusion
• Water is held within pore spaces and is available for plant growth
  • Water gets into the soil through precipitation or irrigation

Components Proportion

• The proportion of soil's components depends on soil type, management, climate, and mineral particle size

Soil Components Origin

• Mineral particles, occupying the largest volume, are created by weathering and erosion of parent rock
• Weathering breaks rocks into smaller particles
• Particle movement is erosion
• Weathering has various forms:
  • Physical weathering is caused by frost, heat, water, ice, or wind
  • Chemical weathering is caused by carbonic acid, made from carbon dioxide and water, which reacts with alkaline minerals
  • Biological weathering is caused by plant roots, animal movement, and organisms producing carbon dioxide

Soil Particle Classification

• Soil particles can be classified into three groups according to their size
• Sand has a gritty texture, large pore size, drains well and contains large air spaces, with particles sized between 2.0 - 0.02 mm
• Silt has a silky or soapy texture, less friction than sand and slippery particles, with particles sized between 0.02 – 0.002 mm
• Clay has a sticky texture when wet, holds particles tightly, has poor air spaces and drainage, and forms a hard mass when dried with particles sized less than 0.002 mm

Soil for Plant Growth

• Successful plant growth requires nutrients, anchorage, water, and oxygen for root respiration

Elements Supplied

• Plants need nitrogen, phosphorus, potassium, and other elements for proteins and life processes
• Nitrogen is supplied as nitrate ions (NO-3)
• Phosphorus is supplied as phosphate ions (PO4-3)
• Potassium is supplied as potassium ions (K+)

Organic Content

• Organic content involves decomposers that produce humus, which is rich in nutrients

Soil Decomposers & Breakdown

• Earthworms break down vegetation, mix and aerate the soil, and spread organic matter
• Fungi feed on dead matter, digest woody items, and aid nutrient uptake
• Bacteria work on organic matter, convert waste into chemicals, and convert nitrogen to nitrates

High Levels of Organic Matter

• High organic matter increases water-holding capacity, air spaces, decomposers, and prevents mineral nutrient loss

Soil pH

• Soil pH depends on parent rock and water pH
• Affects nutrient uptake and availability
• Farmers adjust pH by acidifying with acidic fertilizers or alkalizing with ground limestone

Mineral Nutrient Deficiency Signs

• Nitrogen deficiency causes slow growth and yellowing leaves (oldest first)
• Phosphorus deficiency causes dull, blue-green leaves that fall early
• Potassium deficiency causes poor fruit and seed quality, with leaves having brown edges
• Sulfur deficiency causes yellowing of leaves (youngest first)
• Calcium deficiency causes plant tissue death and poor fruit storage
• Magnesium deficiency causes yellowing between leaf veins and early leaf fall
• Iron deficiency causes yellowing between the veins of the youngest leaves
• Copper deficiency causes dark green leaves that become twisted and withered (young leaves first)
• Zinc deficiency causes leaves with poor development and small size
• Boron deficiency causes misshapen leaves and hard areas in fruits

Sandy Soil vs Clay Soil

• Sandy soils have larger air spaces and drain well, but have poor humus retention and are easier to cultivate
• Clay soils have poor air spaces and drainage, but retain humus and are hard to cultivate
• Adding organic matter reduces negative impacts, providing water-holding capacity to sandy soils and increasing air spaces in clay soils

Agriculture

• Agriculture is cultivating animals, plants, and fungi for food and products to sustain human life
• It depends on climate, culture, technology, and economics.

Agriculture Types

• Subsistence agriculture cultivates food for the farmers and their families, with surplus bartered for goods, examples include wheat and rice
• Commercial agriculture cultivates food for sale, with some food for the farmers examples being tea, coffee, cocoa, sugarcane, cotton, rice, wheat, and corn
• Arable agriculture produces plants for human consumption, examples include rice, wheat, maize and soybeans
• Pastoral agriculture produces animals or related products, examples include grass/grain (to feed the animals), milk, wool eggs
• Mixed agriculture involves farms that grow crops for food and rear animals

Production Types

• Extensive production occurs when there is a small amount of production from a large area of land
• Intensive production occurs where large amounts are produced from small areas of land

Increasing Agricultural Yields

• Food demands are increasing along will global population, creating pressure on food production due to:
  • An increasing world population needing more resources
  • Climate change and affecting the availability of fertile farmland.
  • Increases in the standard of living creating a demand for more food variety
  • Increasing settlement sizes reducing available farmland
  • Larger populations impacting the availability of water for irrigation.

Improving Crop Yields

• Crop rotation involves growing different plants in different plots each year to address:
  • Repeated planting leading to disease build-up
  • Increase pest incidence
  • Soil nutrient depletion
• Crop rotation divides a large plot into four smaller areas, each with a plant type:
  • Legumes have nitrogen-fixing bacteria
  • Leafy crops require nitrogen left by legumes
  • Root crops have deep root systems
  • The land is left fallow by planting and allowing to grow wild for a number of years

Crop Rotation Advantages

• Leaving diseases and pests behind in the prior soil
• Allowing the new soil to have essential nutrients
• Having crops ready to harvest at different times to reduce potential waste and to even out the labor and machinery needed

Fertilizers

• Fertilizers contain minerals such as nitrogen, potassium, and phosphorus to supplement available nutrients

Types of Fertilizers

Irrigation

• Irrigation supplies water to crops, which is important because:
  • Plants consist of high percenttage of water
  • Cells require water for activity
  • Photosynthesis requires water
  • Soil requires water to uptake mineral nutrients
  • Water should be pollutant-free and low in salt

The process of supplying water involves: - Storage of water - Transportation of water to the required site - Application of water to the plant

Water Application Methods

• Overhead sprinklers are easy to set up and cover large areas, but can cap the soil, be blown away, and evaporate quickly
• Clay pot irrigation systems use simple technology, are easy to check, and have high efficiency, but are only suitable for permanent plants and have high labor costs
• Trickle drip systems place water at the base of the plant, are automated, and use water efficiently, but are expensive, complex to maintain, blockable, and inflexible
• Flood irrigation is inexpensive and covers large areas quickly, but is inefficient, damages soil structure and wastes water

Controlling Competing Organisms

• Undesirable plants should be controlled because they:
  • Can compete with crops for light and nutrients
  • Reduce seed or grain quality
  • Can be poisonous
  • Can make cultivation difficult
  • Can lead to too much growth in drainage systems
  • Can be a source of pests and diseases
  • Can leave impact on tourism areas by looking untidy
• Herbicides are weed-killing chemicals for large areas
  • Advantages include an easier process to manage and the ineffectiveness of other alternatives

Alternative Weed Control

• Cultural Controls
  • Hand weeding
  • Hoeing
  • Weed barriers.
  • Flame guns

Controlling Pests and Diseases

• Pesticides control pests, with insecticides controlling insects and fungicides controlling fungal diseases

Alternatives to Insecticides

• Biological control means finding natural predators

Mechanisation

• Mechanization allows larger cultivation areas and reduces labor cost
• Ploughing can be done in heavy soil
• Attachments can apply fertilizers/pesticides
• Tractors can transport loads
• The process of selective breeding consists of : - Picking parents that show the sought after characteristcs - Raising said off spring - Pickingthe offspring that show the characteristics and
  • Repeat the prior process

Selective Breeding Drawbacks

• Can be a slow process with a low change of success

GMO (Genetically Modified Organisms)

Controlling Crop Environments

• Large areas cannot be controlled easily, but techniques include cattle shade, windbreaks, and removing trees that shade crops
• Greenhouse manages environment for plant growth

Growth Factor Controls

• Growing blueprint is used to identify the ideal environmental conditions for maximum plant growth

The Greenhouse Effect

• Greenhouses heat up from rays that can be turned heat when passing through transparent material on the inside

Hydroponics

• Hydroponics grows plants without soil via dissolved nutrients

Key Terms

• Legumes: plants with nitrogen-fixing bacteria producing nitrate
• Gene: DNA sequence responsible for a living organism's characteristics
• Genetically modified organism (GMO): organism with altered genetic material

The Impact of Agriculture

• Agriculture uses a lot of chemical that have both intended and unintended impacts

Overuse of Herbicides and Insecticides

• Regular use causes resistance within pest populations
  • A varied amount should be used
• Beneficial insects like bees are affected and the food web is damaged
• Herbicides stay in soil, affecting the next crop
• Heavy rainfall causes chemical leaching into lakes, damaging organisms

Overuse of Fertilizers

• Extra nutrients wastes money and resources if the soil can't contain it;
• Heavy rainfall causes leaching;
• Fertilizers in water lead to eutrophication;
• Nitrates cause diseases;
• pH is affected, availability of minerals;
• Too much reduces plants and produce lots of foliage, but no flower.
• Strict limits are needed; can replace with organic fertilizers

Misuse of Irrigation

• Too much irrigation causes:
  • Damage to soil structure through soil compaction
  • Plant roots die
  • The loss of nutrients that have been dissolved
  • Soil erosion, hard surface, surface content and cultivations issues

Soil Problems

• Overproduction and waste from unsold crops
• Exhaustion of mineral ion content
  • Farmers use the same soil too much with no rest, leaving nutrients depleted
  • Can be resolved through crop rotation

Cash Crops

• Cash crop are more common than crops grown for food leading to a food shortage

Mechanization Impacts

• Machines allow larger cultivated areas, removal of habitats as well as non-renewable enery consumption
• Machines cause soil compaction, can affect job opportunities

Soil Erosion

• Soils that are cultivated regularly tend to lose the structure through the breaking down on of smaller components

Soil Erosion Causes

• Removal of natural vegetation reduces root binding, so flash flooding and rainwater runoff pick the soil
• Overcultivation breaks soil into smaller particles carried by wind
• Overgrazing reduces vegetation, compacting soil
• Wind erosion is increase by Deforestation, increase in need for space, increase in developed space

Water Erosion

• Occurs when water erodes ways such as
  • Heavy rainfall carrying away particles
  • rainwater run-off excess
• soil with no absortion ability will allow rain

Erosion Impacts

• Topsoil erosion impacts organisms
• Silting impacts water courses
• Silt deposits affect water qualirty

Desertification

• Desertification is the process by which fertile land becomes dry
  • Severe droughts lead to migration of the whole community as well as famine and food shortage.

Managing Soil Erosion

• Terracing prevents rainwater soil erosion on steep slopes, commonly used for rice cultivation
  • water is held in the flat areas
• Contour ploughing involves ploughing along the contour in a parallel way creating ridges and troughs
  • Each creates a water barrier protecting from gullies & run off
• Bunds are artificial banks at the edges of growing spaces to hold back water, commonly used for rice cultivation.
• Increases fertility of the soil.
• Windbreaks are barriers that reduce wind impact
  • Without = eroded away
  • Solidy and permeable exist
• Permeable stuctures allow wind to pass and decrees wind speed
• Roots prevent erosion due to run off
• Addition: Create a habitats for insects

Maintaining Crop Cover

• Sowing legumes after crop harvest prevents soil erosion and provides more nitrogen for the next major crop
  • legumes provide nutrients for when the land is ploughed

No Dig Method

• Existing vegetation is left until the current crop is gorwn
  • Harbicides used to prevent growth
  • Vegetation protects major point from being overgrown
• Can give risks such as herbcide build up

###Organic Matter Addition

• Used to improve the soil structure.

• Multi layer approach is cropping

• Trees act as wind barriers

• Provide animal habitata. Fall leave also add to the oil

Mixed Cropping

• Crop rotation maximises the use of spcae

Sustainable Agriculture

• Focuses on meeting population needs as well as following the proccesses of ecology

Irrigation Types

• Use varities of plants that are suited for differen things for effiency

Irrigation With Trickle Drip

• Creates sustainabily and minimise waster while targerting

Rainwater Harvesting

• Collection of rain from roofs

Resistance

• Ability for an orgasim to live through a toxic chemical

Eutrophication

• A sequence events starting with enrichment of water by mineral nutrients or organic that leads to a reduction in oxygen levels in the water and the death of fish and other animals.

Osmosis

• Process in which mineral molecules pass through the the membrane from a weaker to a a stronger solution

Desertification

• Process where the where to soil comes desert.

Famine

• Lack of food access

Terrancing

• Development of the artificial for in a slope terrain.

Intercropping

• Growing other corps around a main crop