soil fertility

• organic fertilisers


  • organic fertilisers are animal and plant materials that release nutrients as they decompose
  • they include: faecal material: manure/sewage sludge, animal food production wastes: bone meal/fish meal/dried blood, plant food production wastes: crop harvest wastes/composted plant waste
• advantages of organic fertiliser

  • many are waste products and may be locally available
  • they increase the soil humus content
  • they increase soil biota populations
• disadvantages of organic fertiliser

  • the nutrient composition cannot be controlled
  • nutrients are released slowly as the material decomposes, so they must be used as part of a long-term cultivation plan
  • many are bulky with a high water content so transport is expensive
  • they usually cannot be added to a growing crop
• advantages of inorganic fertiliser

  • the nutrient composition can be controlled to meet specific crop requirements
  • the nutrients are released rapidly
• disadvantages of inorganic fertiliser

  • some require large amounts of energy during manufacture by the chemical industry
  • they do not add organic matter to the soil, so humus levels and soil biota populations may decline
  • some are toxic to worms
  • some have high solubility and may be leached after application
  • raw material supplies for manufacture may be limited, for example, phosphate rocks
• hydroponics

  
  

  • involves the growth of crops in a nutrient solution rather than a solid growth medium
  • it is usually carried out in greenhouses as part of an intensive system
  • productivity is maximised by controlling limiting factors as much as possible
• advantages of hydroponic production

  • nutrient supply is optimal so this is not a limiting factor for growth
  • all the roots are in contact with the nutrient medium, so the roots are smaller and more growth is directed into the harvestable crop
  • there is no soil to hold pathogens
  • there are no weeds
  • the harvested crop still has roots so it stays fresh longer
  • the harvested crop is attractive for consumers as it has no soil on it
• disadvantages of hydroponic production

  • intensive production involves high inputs of nutrients and energy
  • a high level of technical knowledge is needed