Theory question 102
Soil Fertility and Plant Nutrition(a) Explain four ways in which nutrients are depleted from the soil.
(b) Give three: (i) advantages of applying green manure to soils. (ii) disadvantages of applying green manure to soils
(c) Give four reasons why deforestation should be discouraged in West Africa.
Show the model answer
(a) Any four, explained: leaching – rain water washes soluble nutrients down beyond the roots; crop removal – harvested crops and grazed plants carry nutrients away; burning – bush burning destroys organic matter and nitrogen goes off as gas; erosion – fertile topsoil is washed or blown away; continuous cropping without replacement; oxidation/denitrification losses of nitrogen.
(b)(i) Any three: adds organic matter and nutrients (especially nitrogen from legumes); improves soil structure, aeration and water holding; increases soil organisms; reduces erosion; cheap.
(ii) Any three: labour intensive; land is out of use while the green manure grows; slow release of nutrients; bulky; may encourage pests or weeds; depends on rainfall.
(c) Any four: prevents soil erosion and loss of fertility; checks desert encroachment; protects wildlife and biodiversity; reduces global warming/climate change; keeps rainfall and water supply steady; prevents flooding; preserves timber and other forest products for the future.
Explain how each loss happens.