Agricultural Science 2015 Jamb Examination

Quarantine is a regulatory method used to control the spread of plant diseases by restricting the movement of infected plant materials across regions. By isolating affected crops or preventing the introduction of potentially harmful organisms, plant health can be safeguarded at a national or regional level. Rouging, crop rotation, and soil tillage are cultural practices, but quarantine is strictly a government-enforced regulatory control measure.

Nitrogen is a vital element for chlorophyll production and protein synthesis in plants. Deficiency symptoms usually appear first in older leaves because nitrogen is mobile and moves to younger tissues when scarce. In maize, a lack of nitrogen manifests as yellowing (chlorosis) starting from the lower leaves while the upper leaves remain greener for longer. Other nutrients such as potassium and phosphorus cause different deficiency symptoms like stunted growth, poor root formation, or marginal leaf burns, but nitrogen deficiency is specifically associated with yellowing of older leaves.

Swollen shoot disease of cocoa is a viral disease transmitted mainly by mealybugs. These insects feed on the sap of cocoa plants and transfer the virus from infected plants to healthy ones. Stem borers cause mechanical damage, whiteflies are vectors for other viral diseases, and scale insects mainly suck sap and reduce plant vigor but are not responsible for swollen shoot transmission.

Arid regions are prone to desertification due to low rainfall, sparse vegetation, and strong winds. Establishing forests in these regions helps reduce desert encroachment by binding the soil with tree roots, reducing wind erosion, and improving microclimatic conditions. While firewood, bush meat, and aesthetic values may be by-products, the primary reason is to act as a barrier against desert advancement.

Farm mechanization in West Africa faces challenges such as land fragmentation, which makes it difficult for large machines to operate efficiently, high costs of machinery and maintenance, and the need for skilled operators and technical know-how. However, the availability of spare parts is not generally considered a limitation, though sometimes accessibility may be an issue in remote areas. The major limiting factors are fragmentation, cost, and expertise.

Tsetseflies thrive in forested and humid zones of West Africa. They transmit trypanosomiasis, a deadly disease to animals like cattle, horses, and donkeys used for traction. This makes it difficult to rely on animal power in these regions. While rainfall, culture, and topography may influence farming systems, the direct limiting factor is the presence of tsetseflies.

Land preparation follows a specific order to ensure efficiency. First, the plough is used to break and turn over the soil. Next, the harrow is used to break clods into finer particles and level the soil surface. Finally, the ridger is used to make ridges for planting crops. Therefore, the correct sequence is plough → harrow → ridger.

Staking involves supporting tomato plants with sticks or ropes to keep them upright. This prevents fruits from touching the soil, thereby reducing fungal infections and rotting. It also improves air circulation and exposure to sunlight, leading to healthier plants. While staking may indirectly aid growth and ripening, the main reason is to prevent fruits from rotting on the ground.

Volcanic eruptions produce igneous rocks such as basalt and pumice. Granite is also an igneous rock formed from cooled magma, though more commonly intrusive. Limestone, sandstone, shale, marble, and gneiss are sedimentary or metamorphic. Therefore, the group basalt, granite, and pumice is correctly linked with volcanic origin.

Sub-surface irrigation delivers water directly to the root zone through underground pipes. This method reduces evaporation losses and minimizes weed and pest infestation since the surface remains relatively dry. It is also suitable for soils with low water-holding capacity because water reaches the roots directly. However, it is not restricted to only specific crops; its applicability is wider though it requires technical setup. Hence, option B is not a true advantage.