(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.