SOIL CONSERVATION
Reforestation: Replanting of trees reduces force of wind speed and also reduces the force of the raindrops. The roots of trees also help hold soil particles into crumbs and the dead leaves that drop allow penetration of water and thus preventing run off erosion.
Bush fallowing: This is the allowing of land to rest to bush after a farming period. This allows naturally occuring plants to re-fertilise the soil by the decay of their organic matter.
Terracing and contour ploughing: These two practices which are done along the contours across a hill put successive barriers which prevent soil erosion.
Strip cropping: This is the cultivation of broad strips of crops along the contours of a slope and these alternate with cover crops like grass or sweet potatoes which hold back any water running off.
Manuring: Application of organic matter may be by adding farmyard manure or compost manure decayed by bacteria and fungi This adds plant nutrients into soil.
Mulching: This invloves covering soil surface with dry grass. It reduces the impact of rain drops, reduces evaporation of water from soil and decays to form humus with plant nutrients.
Crop rotation: This is the growing of different crops on a plot of land every year.
¬ Crops included in a rotation should make different demands on soil; and should have varying root depths to draw on different levels for mineral salts.
¬ A rotation does not increase fertility; so there should be regular addition of manure or artificial fertilizers.
¬ A rotation should include legumes because they fix nitrogen into the soil.
¬ Deep rooted crops like cassava in a rotation help to increase soil depth by breaking up subsoil.
¬ Crop rotation prevents establishment of a crop pest or disease.
- Artificial fertilizers: Potassium is supplied as potassium sulphate, nitrogen as ammonium sulphate and phosphorus as calcium phosphate.
Disadvantages of artificial fertilizers.
¬ Continual application of fertilizers does not replace humus so that erosion may be accelerated.
¬ Excess salts could also leach into rivers causing overgrowths of phytoplankton algae resulting in eutrophication.
The process of eutrophication:
- Since continual application of artificial fertilizers reduces humus content, there will be deteriorating crumb structure and soil aeration will be reduced.
- So the plant roots will be deprived of oxygen and so can not absorb salts effectively.
- The unabsorbed nitrates eventually drain into rivers and lakes where they stimulate excessive growth of microscopic plants like phytoplankton algae.
- The overgrowths of algae die and their decomposition depletes oxygen for aquatic animals which also die.
- These deaths and decompositions result into a foul mud.
- This over-fertilisation of rivers and lakes due to sewage disposal or over-application of fertilizers leading to excessive plant growth is called eutrophication.