Soil fertility

• soil fertility - how good the soil is for growing food
• Water content importance

  • Water is used for food transport to dissolve minerals in
  • keeps cells turgid so the plants don't wilt and maximises light absorbance.
  • water is also needed for photosynthesis
  • Too high water content leaches nutrients out of the soil and biota is pushed out
• Soluble Materials importance

  • plants take in nutrients by root absorption e.g:
  • nitrates for amino acids and proteins
  • phosphates for DNA, ATP, cell membranes
  • potassium
  • increasing soluble materials increases fertility
• Air content importance

  • Plants need oxygen to respire and build cell walls with energy
  • nitrogen fixation, ammonification, oxidation, decomposition are aerobic processes performed by soil biota that require air
• Dead Organic Matter importance

  • DOM contains nutrients like phosphates and nucleotides that are important for crop growth.
  • Plants can only access nutrients after decomposition of DOM
  • DOM retains a lot of water (moisture)
• pH importance

  • 5.0 to 7.0 is optimum
  • Optimum pH means optimum enzyme function
  • too acidic = denatured enzymes and biota dies
  • too alkaline = enzymes slow down, crops can't absorb nutrients fast enough and alkali doesn't let nutrients dissolve in it
• Soil biota importance

  • Biota are decomposers and detritovores e.g earthworms that aerate soil
  • Biota decompose dead organic matter to release nutrients
  • All nitrogen processes are done by soil biota
  • Too many biota = nutrients get used up
  • Too few biota = not enough nutrients are released from DOM
• Soil depth importance

  • Deeper soil stores more nutrients
  • it needs to be deep enough for plant roots to grow big enough to allow stability
• Soil texture importance

  Sand is large particles, silt is smaller particles, clay is very small particles

  • Sand is easy to move through as the gaps between the particles are large - root penetration and infiltration are easy
  • Clay is very hard to move through because the gaps between particles are very small - root penetration and infiltration are hard
  • Soft soil allows plant roots to grow more easily to provide stability and source nutrients
• Soil structure importance

  • Sand, silt and clay clump together to form aggregates which clump together to form peds.
  • Platy peds are longer
  • Crumb peds are shorter
  • Water and air can move more easily through crumb peds so smaller peds = higher fertility
• Composition of soil:

  minerals/rock - 40%

  organic matter - 40%

  empty space including air and water - 20%

  biota (bacteria, plants, animals) - 1%
• Soil has a high thermal capacity when it has a high water content
• Crumb peds and a sandy texture makes the soil easy for roots to penetrate and makes it more permeable to water