Soil fertility. 

Soil fertility. 

This is the ability of the soil to supply plants with nutrients in appropriate quantities to sustain their growth. Soil fertility may be sustained through crop rotation, manuring, addition of fertilizers, fallowing, reducing soil erosion, etc.

Loss of soil fertility.

Soil fertility may be lost through;

  1. Monocropping.
  2. Continous cultivation/ploughing.
  3. Leaching.
  4. Soil erosion.
  5. Crop removal from the soil/harvesting.

Soil erosion.

This is the removal of top soil by agents of erosion e.g. running water, air,

Factors aiding/promoting/influencing soil erosion.

  1. Topography.
  2. Burning of surface vegetation.
  3. Construction/mining/brick making/quarrying.
  4. Deforestation.
  5. Over grazing.
  6. Amount and intensity of rainfall.
  7. Type of soil e.g. sand soils are more easily detached and carried away than clay soils. Types of soil erosion.
  8. Sheet erosion.
  9. Rill erosion.
  10. Gulley erosion.
  11. Splash erosion.

Soil and water conservation.

Conservation is preservation or restoration of the natural environment (or sustainable use of a resource).

Preservation methods include;

  • Afforestation/reafforestation.
    • Contour farming.
    • Terracing.
    • Mixed cropping/Intercropping.
    • Crop rotation.
    • Strip cropping.
    • Mulching.
    • Cover cropping.
    • Grassed water ways.
    • Trash or stone lines.
    • Barriers.
    • Ridging.
    • Wind breaks.

Effects of soil erosion.

  • Loss of plant nutrients and micro-organisms, hence reduce crop yield.
  • Damage to crops.
  • Silting of dams, lakes, rivers/water pollution.
  • Degradation of the land.
  • Shortage of water as soil displaces water in rivers.
  • Increase cost of agricultural production through application of manures, artificial fertilizers, etc.

Ways of improving soil fertility.

Soil fertility may be improved through;

  • Application of fertilizers/manures.
  • Crop rotation.
  • Fallowing i.e. leaving land uncultivated/to rest. ü Afforestation and reafforestation.

Nitrogen cycle.

Nitrogen is fixed into an inorganic form e.g. nitrates and ammonia before it is used by the plants and animals. Nitrogen may be fixed through;

1:Nitrogen fixation.

Through,

  1. Thunderstorms.

The energy of lightening combines atmospheric nitrogen and oxygen together to form oxides of nitrogen. These oxides combine with rain water to form acidic solutions which reach the soil through rainfall. In the soil the acid combines with chemicals to form nitrates that can be availed to the plants.

  • Nitrogen fixing organisms.

These include symbiotic Rhizobia and free living bacteria like

Azotobacter and Clostridium. They fix the atmospheric nitrogen into plant roots and soil respectively which is used to make plant proteins and amino acids.

  • Ammonification.

 This is where putrefying bacteria and fungi decompose the dead bodies of animals and plants into ammonia, carbon dioxide and water. Ammonia is also formed from faeces of animals. 

2:Nitrification.

This is where ammonia is converted into nitrates from ammonium compounds by Nitrobacter and Nitrosomonas.

Denitrification.

Some organisms in the environment break down nitrates into nitrogen thus releasing nitrogen into the atmosphere. E.g. bacteria like pseudomonas and some fungi.

image 2
A-Nitrogen fixed by electrical discharge into the soil. B-Denitrifying bacteria. C-Nitrogen fixing bacteria (e.g. Azotobacter). D-Nitrates absorbed by plants to make plant proteins. E-Nitrogen-fixing bacteria in root nodules of leguminous plants. F-Feeding by animals. G-Death and decay. H- Excretion and faeces. I- Nitrifying bacteria (e.g. Nitrosomonas). J-Nitrifying bacteria (e.g. Nitrobacter).
 
Carbon cycle.
Carbon dioxide is removed from the atmosphere by plants through photosynthesis. It is released into the atmosphere through combustion, decay and respiration.


 

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