Field Crop currently grown Soil pH 1 Pineapple 4.8 2 Cowpea 6.2 3 Cabbage 7.5 6 A farmer collected soil samples from three different fields on the farm and ...

(a) Field with the most acidic soil [1]

Field 1, with a pH of 4.8. [1] This is well below the neutral point (pH 7) and lower than both Field 2 (6.2) and Field 3 (7.5).

(b) Material to raise the pH of Field 1 [1]

Lime (calcium carbonate / ground limestone / dolomite / wood ash). [1] Liming is the standard practice for correcting acidic soils. The calcium carbonate reacts with hydrogen ions in the soil, neutralising the acidity and raising the pH toward a more favourable range for crop growth.

(c) How low pH reduces crop growth [2]

1. Low pH reduces the availability of essential nutrients such as phosphorus, calcium, and magnesium, because these elements become chemically locked in insoluble forms that plant roots cannot absorb. [1]
2. At the same time, low pH increases the solubility of toxic elements such as aluminium and manganese to levels that damage root cells, inhibiting root growth and water uptake. [1]

(d) Most suitable field for groundnuts (pH 5.5-6.5), and why [2]

Field 2 (pH 6.2) is most suitable. [1] Its pH of 6.2 falls within the preferred range of 5.5 to 6.5 for groundnuts, meaning nutrient availability will be optimal and there is no need for liming or acidification. Field 1 (4.8) is too acidic, and Field 3 (7.5) is above the preferred range. [1]

(e) Two factors other than pH that affect soil fertility [2]

Any two of:

1. Organic matter content - humus releases nutrients, improves structure, and supports microbial life. [1]
2. Nutrient content (N, P, K) - the actual supply of essential plant nutrients in the soil. [1]
3. Soil texture - affects water retention, drainage, and nutrient-holding capacity.
4. Soil structure - determines root penetration and aeration.
5. Drainage / aeration - waterlogged soils have low fertility because roots and microbes lack oxygen.
6. Microbial activity - soil organisms cycle nutrients from organic matter into plant-available forms.

(f) How to test soil pH using a field testing kit [3]

1. Take a small sample of soil and place it in the test container or tube provided in the kit. [1]
2. Add the indicator solution or reagent (usually barium sulphate and indicator dye) to the soil sample and mix or shake well to ensure full contact. [1]
3. Allow the mixture to settle, then compare the colour that develops in the liquid with the colour chart provided in the kit. The matching colour indicates the pH value of the soil. [1]