Chapter 2 : Soil The Source of Life

• Soil


  The source of life
• Components of soil


  • Minerals
  • Air
  • Water
  • Organic matter (humus)

  
• Factors that influence soil formation

  • Parent material
  • Climate
  • Organisms
  • Relief
  • Time

  
• Parent material


  Can be either organic or inorganic
• Soil erosion


  1. Movement of sand

  2. Bigger stones seen because finer sand has been blown away
• Physical properties of soils

  • Water penetration
  • How long water stays in soil
  • How well the soil holds up under machinery
  • Ease of root penetration
  • Aeration of the soil

  
• Soil particle sizes


  • Sand: 0.05-2mm
  • Silt: 0.002-0.05 mm
  • Clay: smaller than 0.002mm

  
• Loam soils


  52% sand, 28-50% silt and 7-27% clay
• Soil horizons


  • O-horizon: un-decomposed and decomposed material (5 cm – topsoil)
  • A-horizon: top soil, organic matter and mineral elements – darker 25 cm – 1m
  • E-horizon: Organic material leached out – light in color
  • B-Horizon: Material leached out. High in clay –O,A,E and B – solum – true soils. Plant roots
  • C-horizon: Parent material
  • R-horizon: Bedrock – not visible

  
• Capillary water


  Held in pores that are small enough to hold water against gravity, but not so tightly that roots cannot absorb it
• Hygroscopic water


  Found not only in pores but also on the surface of soil particles. Tightly held in soil and cannot be absorbed by plants

  
• Gravitational water


  Moves through a soil in the large pores and drains away due to the force of gravity
• Field capacity

  The water remaining in a soil after it has been thoroughly saturated and allowed to drain freely, usually for one to two days
• Permanent wilting point


  The moisture content of a soil at which plants wilt and fail to recover when supplied with sufficient moisture
• pH


  Depends on H+ ions. More H+ = lower pH, more OH- = higher pH
• Farmer must treat pH with lime or acid
• Ideal pH is 6
• Soil fertility


  The soil's ability to supply nutrients to the plant
• Soil negative charge


  Elements have positive charge, so small particles with bigger surface area can attract more elements
• Plants


  • Enrich the environment by providing organic material
  • Photosynthesize and produce sugars and oxygen
  • Filter the air, water and the soil in which they grow
  • Prevent soil erosion
  • Absorb CO2 and purify the air
• Rhizobium bacteria


  Make nitrogen available to the plant
• Mycorrhiza


  Symbiotic relationship between a fungus and plants. Plants provide sugars to fungi and the fungus provides water and nutrients such as phosphates to the plants
• Earthworms


  • Provide nutrients to other organisms such as felts, hedgehogs and frogs, as well as to plants
  • Provide aeration (Oxygen) in the soil
• Characteristics


  • Some are dominant (R)
  • Others are recessive (r)
• Crossing two pure bred lines

  1. Homozygous RR or rr

  2. Cross two homozygous genes with each other
• Example of crossing


  • Red flowers (RR) and white flowers (rr)
• R is dominant for red flowers and r is recessive for white flowers
• Crossing two heterozygous lines (Rr)


  Three red flowers will be produced and 1 white flower
• Transgenic plant


  Plants with new characteristics
• Chromosome


  • All genetic material is grouped together
  • Consist of two chromatids with DNA on each chromatid
  • DNA divided into segments known as genes responsible for certain traits

  
• Meiosis


  The 2 chromosomes separate from each other and the offspring receive one of each parent
• Organism


  • Most have two sets of chromosomes
  • Humans have 23 chromosome pairs
  • Some plants have more than 2 sets of chromosomes and are called polyploid

  
• On each chromatid lay double helixes of DNA string
• Transcription


  Occurs in the nucleus of the cell
• Translation

  Occurs in the cytosol of the cell
• Plant breeding


  • Very long process (around 10 years)
  • Not very effective (only 1% of plants good enough to use as parents for the next generation)
• Genetic engineering

  More effective and faster than plant breeding
• People are resistant to genetic engineering due to concerns about side effects