GCE Agricultural Science
Past Questions

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Subsistence agriculture is characterised by small-scale production primarily aimed at feeding the farmer and his family, with little or no surplus for sale. This type of farming is common in rural areas of West Africa and relies mainly on family labour and simple tools.

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Profit = Revenue − Cost = ₦450,000 − ₦180,000 = ₦270,000. Profit margin (%) = (Profit ÷ Revenue) × 100 = (₦270,000 ÷ ₦450,000) × 100 = 60%. Option A (40%) results from dividing cost by revenue; option C (150%) results from dividing profit by cost; option D (250%) is a common arithmetic error from incorrect formula application.

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Commercial farming involves the large-scale production of crops and livestock primarily for sale in order to generate profit. Subsistence farming produces mainly for the farmer's own consumption. Pastoral farming focuses on rearing livestock, and mixed farming combines both crops and livestock.

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Sericulture is the branch of agriculture concerned with the rearing of silkworms (Bombyx mori) and the production of raw silk. Apiculture involves bee keeping, aquaculture deals with fish and other aquatic organism farming, and floriculture is concerned with the cultivation of flowers.

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Mixed farming involves the simultaneous combination of crop cultivation and livestock rearing on the same farm, with each enterprise benefiting the other. In this case, the poultry provides manure for the maize, illustrating the integrated nature of mixed farming. Monoculture involves only one crop, plantation agriculture is large-scale single-crop production, and pastoral farming focuses exclusively on livestock.

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Despite agriculture's critical role in Nigeria's economy, the country still imports significant quantities of food items such as wheat, sugar, and fish to meet domestic demand, so agriculture does not eliminate the need for food importation. The other options are factually correct: agriculture supplies raw materials to industries, contributes substantially to GDP, and remains the largest employer of labour in Nigeria.

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Metallurgy is the science and technology of metals and their extraction, and is not a branch of agriculture. Agronomy deals with field crop production, horticulture involves fruit and vegetable production, and apiculture is the rearing of bees for honey and other products.

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Inadequate capital and poor access to credit facilities remain major constraints preventing Nigerian subsistence farmers from expanding into commercial agriculture, as they cannot afford modern inputs, machinery, or large-scale operations. Arable land availability and rainfall are generally favourable factors, while improved varieties are a positive development, not a hindrance.

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Apiculture is correctly defined as the science and practice of rearing bees, primarily for honey and wax production. Silviculture deals with forest tree cultivation, not fish rearing; agrostology is the study of grasses, not vegetables; and horticulture covers fruits, vegetables and ornamentals, not timber trees specifically.

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Agriculture is broadly defined as the art and science of cultivating the soil, rearing animals, and processing their products for human use and benefit. It encompasses crop production, animal husbandry, and related processing activities. Options A and D are too narrow, while C describes land clearing, not agriculture.

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Soil permeability refers to the rate at which water and air move through soil pores. While texture, porosity, and structure all influence permeability, permeability itself is the specific property that measures the ability of soil to transmit water. It is directly measured in terms of flow rate through a given soil volume.

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Bacteria and fungi are the principal decomposers of organic matter in the soil, breaking down complex organic compounds into simpler inorganic nutrients through mineralisation. While earthworms, nematodes, and millipedes contribute to physical fragmentation and mixing of organic matter, the biochemical decomposition that releases nutrients is primarily carried out by microbial organisms such as bacteria and fungi.

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A soil catena (or toposequence) is a sequence of soils that have developed from the same parent material under the same climate but differ in their characteristics due to variations in topographic position (relief) and drainage. The term was introduced by Milne (1935) in East Africa. Option A describes a climosequence, while C describes a soil profile.

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A loam soil typically contains approximately 25–50% sand, 25–50% silt, and 10–25% clay, with no single fraction dominant. The given composition of 40% sand, 35% silt, and 25% clay falls within the loam textural class on the USDA soil textural triangle. This balanced composition gives loam its favourable agricultural properties.

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Liming is the application of calcium-containing materials to neutralise soil acidity, thereby raising the soil pH. An increased pH improves the availability of most plant nutrients such as phosphorus, calcium, and magnesium, and reduces the toxicity of aluminium and manganese. Liming does not directly add nitrogen or organic matter to the soil.

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Total porosity (%) = [1 − (bulk density / particle density)] × 100 = [1 − (1.5 / 2.65)] × 100 = [1 − 0.566] × 100 = 0.434 × 100 = 43.4%. Option B (56.6%) is the complement error where candidates subtract porosity from 100 incorrectly. A porosity of 43.4% is typical of a moderately compacted agricultural soil.

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The B horizon, also called the subsoil or zone of illuviation, is where materials such as clay, iron oxides, and humus leached from the A horizon accumulate. The A horizon is the zone of eluviation (loss), while the C horizon consists of weathered parent material. The O horizon contains organic matter at the surface.

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Moisture content on a dry weight basis = [(wet weight − dry weight) / dry weight] × 100. Here, [(150 − 120) / 120] × 100 = [30 / 120] × 100 = 25%. Option A (20%) is a common error from dividing by wet weight instead of dry weight. The dry weight basis is the standard method used in soil science.

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Jenny (1941) proposed the CLORPT model of soil formation, where soil is a function of Climate, Organisms, Relief (topography), Parent material, and Time. This sequence is conventionally remembered by the acronym CLORPT. All five factors interact to determine the characteristics of a soil profile.

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Cation exchange is the process whereby negatively charged clay and humus colloids attract and hold positively charged nutrient ions (cations) such as Ca²⁺, Mg²⁺, and K⁺. These cations can be released and exchanged with other cations in the soil solution, making nutrients available to plant roots. This is a fundamental mechanism of soil fertility.

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NPK 15:15:15 means the fertilizer contains 15% nitrogen by weight. Applying 60 kg of this fertilizer gives: $60 \times \frac{15}{100} = 9$ kg of nitrogen. Distractors represent common errors such as using 10%, 20%, or 25% instead of 15%.

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Thinning is the practice of removing excess seedlings from a stand to achieve the optimum plant population per unit area. This ensures that the remaining plants have adequate space, light, water, and nutrients for vigorous growth. It is commonly practised when seeds are sown in clusters or when germination rate exceeds the desired population.

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Organic matter improves soil structure by binding soil particles together into aggregates, thereby enhancing porosity, water retention, and aeration. Soil texture refers to the relative proportions of sand, silt, and clay and cannot be changed by adding organic matter. Soil colour and mineralogy are not primary targets of organic matter incorporation.

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Mixed cropping (also called intercropping) involves growing two or more crops at the same time on the same piece of land. Crop rotation involves growing different crops in sequence over different seasons. Monoculture is the cultivation of a single crop, while relay cropping involves planting a second crop into a maturing first crop before harvest.

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Plant population per hectare is calculated as: $\frac{10{,}000 \text{ m}^2}{0.75 \text{ m} \times 0.50 \text{ m}} = \frac{10{,}000}{0.375} \approx 26{,}667$ plants per hectare. Option A results from dividing by 0.75 alone, option C from dividing 10,000 by 0.50, and option D from using 25 cm × 100 cm spacing.