WAEC Agricultural Science 2024 Theory — Question 2

Model answer

(a) Soil pH is defined as a measure of the degree of acidity or alkalinity of the soil, i.e. a measure of the concentration of hydrogen ions (H+) or hydroxyl ions (OH-) in the soil. A pH scale is graduated from 1-14. A soil whose pH is below 7 is said to be acidic. A soil whose pH is above 7 is said to be alkaline. A soil with pH 7 is said to be neutral. (b)(i) Cover crops are crops that are grown specially to cover the soil and protect it from erosion and leaching for a given length of time. (ii) Advantages: effective in controlling weeds; reduces soil temperature through vegetative cover/reduces direct effect of sunlight on the soil; leguminous cover crops help fix nitrogen in the soil; serves as green manure when ploughed back into the soil; could be harvested as food crop after harvesting the cash crop; prevents soil erosion; reduces soil compaction; improves soil structure; could serve as forage for livestock; controls pests. (c) Wild marigold -- Aspilia africana. Spear grass -- Imperata cylindrica. Stubborn grass -- Eleusine indica. Pig weed -- Amaranthus spp/Boerhavia diffusa. Carpet grass -- Axonopus compressus.