Agricultural Science
WAEC 2019
(a) (i) Define the term drainage.
(ii) State four reasons why waterlogged agricultural land should be drained.
(b)List six factors affecting nutrient availability in the soil.
(c) Complete the table below on the causative organisms of crop diseases.
| Disease |
Causative Organism |
| Rice blast |
(i) |
| Groundnut rosette |
(ii) |
| Cassava mosaic |
(iii) |
| Root knot of tomatoe |
(iv) |
| Maize rust |
(v) |
| Tristeza |
(vi) |
Explanation
(a)(i) Definition of drainage
- Drainage is the removal of excess water/soil moisture from the soil
(ii) Reasons why waterlogged agricultural land should be drained
- Improves soil temperature.
- Improves aeration of the soil.
- Supports the decomposition of organic matter in the soil to enhance the nutrients’ status/enhances mineralization of organic matter .
- Excess salts that would be toxic to plants are removed with drained water
- Improves soil structure
- Makes land available for cultivation/makes tillage operations easy
- Enhances seed germination/proper development of plant
- Regulates soil pH
b(i) Factors affecting nutrient availability in the soil
- Vegetative cover
- Soil type/nature of soil
- Bush burning
- Soil texture
- Soil structure
- Soil pH
- Topography
- Leaching
- Erosion
- Crop removal/weeding
- Soil water content
- Cultural practices adopted
- Activities of soil microorganisms
- Oxidation and reduction
- Nutrient imbalance/excess of other nutrients
(ii) Causative Organisms of crop diseases
| Disease |
Causative Organism |
| Rice blast |
(i) Fungus (Piricularia oryzae) |
| Groundnut rosette |
(ii) Virus |
| Cassava mosaic |
(iii) Virus |
| Root knot of tomatoe |
(iv) Nematode (Meloidogyne spp) |
| Maize rust |
(v) Fungus (Puccinia polysora) |
| Tristeza |
(vi) Virus |
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