Agricultural Science 2020 Jamb Examination

Crop rotation is an agricultural practice where different crops are planted in succession on the same land to maintain soil productivity. It helps replenish soil nutrients, reduces the build-up of crop-specific pests and diseases, and improves soil structure by alternating between deep-rooted and shallow-rooted crops. However, it does not predispose the soil to leaching. Instead, leaching is mainly influenced by excessive rainfall, poor soil type, and lack of proper land management. Therefore, crop rotation is beneficial rather than harmful in this regard.

Igneous rocks are formed from the cooling and solidification of molten magma. Granite is a well-known igneous rock composed mainly of quartz, feldspar, and mica, giving it a coarse-grained texture. Gneiss is a metamorphic rock, limestone is sedimentary, and sandstone is also sedimentary. Hence, granite is the correct example of an igneous rock.

Biotic factors are living components that affect agricultural production. Examples include predators, pests, parasites, and diseases. Predators, such as birds or insects that feed on crops or livestock, directly influence productivity. Rainfall, soil structure, and wind are abiotic (non-living) factors. Therefore, predators are biotic influences on agriculture.

Macronutrients are mineral nutrients required by plants in large quantities, such as nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur. Phosphorus plays a major role in energy transfer, root development, and flowering. Zinc, iron, and manganese, though essential, are required in very small quantities and are classified as micronutrients.

Marketing boards were established by the government to regulate and promote the sale of cash crops such as cocoa, groundnut, and palm produce. They guaranteed stable prices, provided a ready market for farmers, and helped encourage production. Schools of agriculture and extension offices provide education and training, while markets exist for sales but are not government-established structures for stabilising trade.

In a plough, the mould board is the curved surface that turns over the cut slice of soil. It works in conjunction with the plough share, which cuts into the soil, while the mould board lifts and inverts it. The hitch is the connecting point to the tractor or draught animal, and the handle provides control. From the diagram, the part labelled I corresponds to the mould board.

The diagram depicts latex tapping, which involves cutting grooves into the bark of a rubber tree to extract latex. This method is unique to Hevea brasiliensis, the natural rubber tree. Theobroma cacao produces cocoa pods, Zingiber officinale is ginger, and Gossypium hirsutum is cotton, none of which are tapped for latex.

The tool shown is a budding knife, which is specifically designed for budding, a vegetative propagation method. In budding, a bud from a desired plant is inserted under the bark of a rootstock so that it grows and forms a new plant. This knife allows precise cuts necessary for successful budding, unlike seed planting, transplanting, or layering which require different tools.

The tool in the diagram is long and narrow, resembling a tapping knife used in rubber plantations. It is designed to make precise cuts into the bark for latex collection. Secateurs and shears are for pruning, while cutlasses are for clearing. Thus, the tool is most accurately identified as a knife.

The diagram represents the law of diminishing returns, where output increases initially with added input, but eventually the rate of increase slows and becomes uneconomical. Point III typically represents the stage where the marginal returns begin to decline, meaning further input would not significantly increase output and may reduce profit. Thus, the rational decision is to stop at point III.