7 An agricultural extension officer visited two farms in different climate zones. Farm P is in a hot, dry savanna region and Farm Q is in a cool, wet highla...

(a) Soil temperature differences between the two farms during the growing season:

1. Farm P (hot, dry savanna) has higher soil temperatures because it receives intense solar radiation with less cloud cover, and the higher ambient air temperature heats the soil surface directly. Dry soils also warm up faster because there is less water to absorb heat energy (water has a high specific heat capacity). [1]
2. Farm Q (cool, wet highland) has lower soil temperatures because of higher altitude (temperature drops approximately 6.5 degrees Celsius per 1000 m elevation gain), greater cloud cover that blocks incoming solar radiation, and wetter soil that absorbs more energy before its temperature rises. [1]

(b) Two effects of high soil temperature on soil organisms:

1. Death or dormancy of microorganisms - at very high temperatures (above 40-45 degrees Celsius), many beneficial soil bacteria and fungi are killed or become inactive because their cellular enzymes denature. This reduces the microbial population responsible for decomposing organic matter and releasing nutrients. [1]
2. Reduced earthworm activity - earthworms are sensitive to heat and will burrow deeper into the soil or become dormant when surface temperatures are too high. Since earthworms are major contributors to soil aeration, mixing, and organic matter incorporation, their retreat reduces soil health. [1]

(c) One method to reduce soil temperature at Farm P, with an explanation of how it works:

Apply mulch to the soil surface (using dried grass, straw, crop residues, or other organic material).

1. Shading effect - the mulch layer physically blocks direct sunlight from reaching the soil surface, reducing the amount of solar radiation absorbed by the soil. [1]
2. Insulation - the air trapped within the mulch layer acts as an insulator, buffering the soil from rapid temperature fluctuations and keeping it cooler during the hottest part of the day. Mulch also reduces evaporation, maintaining soil moisture, which in turn moderates temperature because wet soil warms more slowly than dry soil. [1]

[3]

(d) The farmer at Farm Q (cool, wet highland) might need raised beds for vegetable production because:

1. Excess moisture and poor drainage - in a cool, wet climate the soil is frequently saturated or waterlogged. Raised beds lift the root zone above the surrounding water table, allowing excess water to drain off the sides and preventing roots from sitting in saturated soil. [1]
2. Improved root health - with better drainage, the root zone has adequate air-filled pore space for aerobic respiration. This prevents root rot and oxygen starvation that would otherwise kill or stunt vegetable crops, which are generally intolerant of waterlogging. [1]