(a) State four characteristics of clay. [4 marks]
(b) Mention four effects of drought on plant growth and development [4 marks]
(c) List two symptoms of phosphorus deficiency in crops. [2 marks]
(d) State three ways in which each of the following soil properties is important in crop production:(i) soil reaction; (ii) soil temperature. [6 marks]
Explanation
(a)Characteristics of Clay:
– Particle size less than 0.002mm/ very fine particles/ smooth texture.
-Very small pore spaces.
-Numerous pore spaces.
– High water holding capacity.
– Hard when dry.
– Poor drainage.
-Very easy to mould into shape/High plasticity.
– It swells when wet and cakes when dry.
– Absorbs and releases heat slowly.
– Sticky when wet.
– Poor aeration.
-High nutrient level/High Cation Exchange Capacity.
-Colloidal in nature.
-High capillarity.
(b) Effects of drought on plant growth and development:
-Delay in flowering/reduction in flowers/flower abortion.
-Poor crop establishment.
-It leads to a reduction in leaf area.
-There is a reduction in cell size and inter-cellular volume.
-Several physiological processes may decrease due to the dehydration of protoplasm.
-Water stress produces important changes in carbohydrate and nitrogen metabolism of plants.
-There is a decrease in the production of green matter.
-There is a reduction in photosynthesis.
-It impairs desired quality, that is, appearance, fibre content, firmness, etc.
-There is reduction in yield.
-Wilting.
-Possible death of plants/crop failure.
– Lower resistance/prone to diseases.
-Difficulty in pegging especially in groundnut.
(c) Symptoms of phosphorus deficiency in crops:
-Purple and brownish colouration of leaves, from tip backwards.
-Stunted growth.
-Poor root development.
-Immature fruit drop.
-Lodging in cereal crops.
(d) Ways in which soil reaction and soil temperature are important in crop production
(i) Soil Reaction:
-It affects the activities of soil micro-organisms.
-It affects the availability of certain soil nutrients.
-It affects the solubility of certain elements which may be toxic to crops at higher concentration.
-It determines the type of crops to grow.
(ii) Soil Temperature:
-The decomposition of soil organic matter is also affected. Influences rate of seed germination.
-Influences the rate of photosynthesis.
-Affects distribution of crops.
– Affects maturity and ripening of crops.
-Influences the rate of evapo-transpiration.
– Influences root development.
– It affects the population of soil microbes.
-Low temperature causes a decrease in metabolic activities and reduction in enzymatic reactions.
-High temperature will also affect the activities of micro-organisms.
– It affects the level of soil moisture, absorption of water and nutrients by roots.