gce model questions vol1 2021 agricultural_science | Essay

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Question 1 View Details
A farmer intends to convert a 5‑hectare monoculture field of maize into a diversified agro‑ecosystem. Discuss the ecological implications of this conversion.
Question Parts
(a)
Explain why biodiversity is important for the productivity and resilience of agro‑ecosystems.
(b)
Analyse the likely effects of the existing monoculture on soil health and suggest two soil‑conservation practices that could mitigate these effects.
(c)
Propose an integrated pest‑management (IPM) strategy for the new diversified system, highlighting at least three control measures.
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Question 2 View Details
The diagram shows the laboratory set‑up used for the gravimetric hydrometer method of soil‑texture analysis.
Question Parts
(a)
State the principle on which the hydrometer method determines the proportions of sand, silt and clay in a soil sample.
(b)
Using the diagram, outline the step‑by‑step procedure for determining the percentage of sand, silt and clay in a 50 g air‑dried soil sample.
(c)
The hydrometer reading at 40 s is 1.025 g cm⁻³ and at 2 h is 1.015 g cm⁻³. Assuming the volume of the suspension is 1000 cm³ and the density of water is 1.000 g cm⁻³, calculate the approximate percentages of sand, silt and clay in the sample.
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Question 3 View Details
A farmer collected a 500 g soil sample from the top 15 cm of a field. The sample was oven‑dried and then separated by wet sieving into sand, silt and clay fractions. The masses obtained were: sand 280 g, silt 150 g and clay 70 g. Explain how the percentages of sand, silt and clay are calculated and discuss what the resulting texture class indicates about the field’s water‑holding capacity and suitability for rice cultivation.
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Question 4 View Details
Soil tests from a 1 ha maize field gave the following extractable nutrient levels: N = 45 kg ha⁻¹, P = 18 kg ha⁻¹, K = 30 kg ha⁻¹. The target yield is 6 t ha⁻¹ and the average nutrient removal rates are N = 20 kg t⁻¹, P = 5 kg t⁻¹ and K = 15 kg t⁻¹. The recommended fertilizer sources are urea (46 % N), single superphosphate (20 % P₂O₅ ≈ 9 % P) and muriate of potash (60 % K₂O ≈ 50 % K). Calculate the amount of each fertilizer (in kg ha⁻¹) required to meet the nutrient deficit, and justify why a balanced application is important for sustainable production.
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Question 5 View Details
A farmer in northern Nigeria has 2 ha of land with sandy loam soil, pH 5.8, low organic matter, an average annual rainfall of 800 mm and a temperature range of 28–35°C. The farmer intends to grow maize as a cash crop and to intercrop it with cowpea to improve soil nitrogen. Answer the following:
Question Parts
(a)
Explain whether the given soil conditions are suitable or unsuitable for maize and for cowpea, citing the relevant soil properties.
(b)
Recommend a soil‑fertility management plan for the maize‑cowpea intercrop. Include (i) the amount of lime required to raise the pH to 6.5 (assume 1 t of CaCO₃ per ha raises pH by 0.2 units in sandy loam), (ii) the rate of organic amendment (apply 5 t/ha of well‑decomposed farmyard manure), and (iii) the nitrogen fertilizer rate needed for maize after accounting for the 30 kg N ha⁻¹ fixed by cowpea. Show all calculations.
(c)
Assuming expected yields of 4 t ha⁻¹ of maize and 1.5 t ha⁻¹ of cowpea, with market prices of ₦150,000 per tonne for maize and ₦120,000 per tonne for cowpea, calculate the gross income from the 2‑ha farm. Then estimate the total cost of the inputs recommended in part (b) (lime ₦10,000 per tonne, organic manure ₦5,000 per tonne, nitrogen fertilizer ₦30,000 per tonne). Finally, compute the net profit.
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Question 6 View Details
A smallholder dairy farmer keeps 8 lactating Friesian cows, each averaging 20 L of milk per day. The cows are fed a total mixed ration (TMR) on a dry‑matter basis consisting of 40% cassava leaf meal, 30% maize grain, 20% groundnut cake and 10% mineral mix. The nutrient composition per kilogram dry matter is: cassava leaf meal 18% CP, 4 MJ ME; maize grain 9% CP, 13 MJ ME; groundnut cake 45% CP, 12 MJ ME; mineral mix negligible CP but supplies required minerals. The maintenance requirement for a 600‑kg cow is 0.5 kg CP and 8 MJ ME per day, and each litre of milk requires an additional 0.09 kg CP and 0.5 MJ ME. Answer the following:
Question Parts
(a)
Calculate the daily amount of crude protein (CP) and metabolizable energy (ME) supplied by the TMR per cow. Show your working.
(b)
Determine whether the ration meets the cows' total CP and ME requirements for the reported milk production. If a deficit exists, suggest a realistic supplement (type and amount) to eliminate the shortfall.
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Question 7 View Details
A farmer cultivates maize on a 5‑hectare field. During a scouting visit he observes stem borer (Busseola fusca) larvae on the crop. The farmer wishes to decide whether to apply the recommended insecticide and, if so, how many larvae per hectare would justify treatment.
Question Parts
(a)
Define the term *economic threshold* (ET) and explain at least three agronomic or economic factors that influence its value for a pest species.
(b)
Given the following data, calculate the Economic Injury Level (EIL) in number of larvae per hectare and then the Economic Threshold (ET). - Average grain loss per stem borer larva = 0.15 kg - Market price of maize grain = ₦120 per kg - Cost of the recommended insecticide per hectare = ₦2 500 - The insecticide kills 90 % of the larvae present. Assume the EIL formula: \[\text{EIL} = \frac{C}{V \times D \times K}\] where C = cost of control per ha, V = market value per kg, D = damage per larva (kg), K = proportion of pest killed. State the EIL (rounded to the nearest whole larva) and then compute the ET as 20 % of the EIL.
(c)
If the farmer’s scouting count shows an average of 12 larvae per hectare, advise whether the insecticide should be applied now, justifying your answer with reference to the ET calculated in part (b).
(d)
List two non‑chemical control methods that could be incorporated into an Integrated Pest Management (IPM) programme for stem borer and briefly explain how each reduces pest pressure.
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Question 8 View Details
A 4‑hectare cassava farm in the Niger Delta region shows the following symptoms: leaf necrosis with brown lesions, wilting of older leaves, and rotting of harvested tubers. The farmer suspects a disease problem and wishes to confirm the diagnosis, predict its spread, and plan control measures.
Question Parts
(a)
Identify the most likely disease, give its scientific name, describe the causal organism and outline the main epidemiological factors that favour its development in the Niger Delta.
(b)
During a six‑week monitoring period the proportion of infected plants was recorded as follows: Week 1 = 5 %, Week 2 = 12 %, Week 3 = 25 %, Week 4 = 45 %, Week 5 = 68 %, Week 6 = 85 %. Assuming the disease follows a logistic growth pattern \[P(t)=\frac{1}{1+e^{-(a+bt)}}\], where P is the proportion infected at week t, use a logit transformation to linearise the data and estimate the parameters a and b (show the calculation steps).
(c)
Using the parameters a and b obtained in part (b), predict the proportion of infected plants at week 8. Comment on the implication of this prediction for the farmer’s planned harvest date (which is at week 10).
(d)
Propose an integrated disease management plan for this cassava farm. Include (i) a cultural practice, (ii) a resistant variety recommendation, and (iii) a chemical control measure, explaining the rationale for each component.
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Question 9 View Details
A cattle farmer in northern Nigeria observes the following in a herd of 120 cattle: sudden high fever (41.5 °C), red swollen lymph nodes, nasal discharge, and a sudden death rate of 15 % within a week. Post‑mortem reveals haemorrhagic lesions in the lungs and liver. The farmer reports that the herd was recently introduced to a new water source that is shared with a neighbouring herd known to have a history of tick infestation.
Question Parts
(a)
Identify the most likely disease affecting the herd and justify your answer using the clinical signs and epidemiological information provided.
(b)
Describe the causative agent, its mode of transmission and the part of its life‑cycle that is most relevant for control on the farm.
(c)
Propose an integrated control programme for the farm, including vaccination, tick control and management measures. Justify each component.
(d)
If each dead animal represents a direct loss of ₦150 000 (including carcass value and replacement cost), calculate the total direct economic loss. Then discuss two indirect losses that could affect the farm’s productivity.
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Question 10 View Details
A mixed farm plans to allocate 10 ha of land for crop production and 5 ha for pasture. The farm intends to raise 80 goats and 30 chickens. The goats require 2.5 kg of concentrate feed per day and 0.5 kg of roughage per day. The chickens require 0.1 kg of concentrate feed per day and 0.02 kg of roughage per day. The farm can produce roughage (grass) on the pasture at a yield of 3 tonnes per hectare per year. Concentrate feed must be purchased at ₦250 per kg. The farm wishes to minimise feed‑purchase cost while meeting nutritional needs. Additionally, the farm aims to generate a net profit of at least ₦2 000 000 per year from the sale of goat meat (average market price ₦2 500 per kg, each goat yields 20 kg of meat) and chicken eggs (average market price ₦150 per dozen, each chicken lays 150 eggs per year).
Question Parts
(a)
Determine the total annual roughage requirement (in kilograms) for the goats and chickens combined.
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