(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
DiseaseCausative 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