neco model questions vol1 2017 agricultural_science | Essay

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Question 1 View Details
A farmer practices mixed cropping of maize and cowpea on a 2 ha field that experiences a dry season followed by a rainy season. Discuss the role of biodiversity in maintaining soil fertility and pest regulation in this system.
Question Parts
(a)
Explain how crop diversity influences nutrient cycling in the mixed‑cropping system.
(b)
Discuss how the presence of two crop species can affect pest populations in the field.
(c)
State why maintaining a field margin with native grasses is important for the ecological balance of the farm.
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Question 2 View Details
The diagram shows a laboratory setup used to determine the infiltration rate of three soil types (sand, loam and clay) arranged in separate columns. Each column is 30 cm tall with a cross‑sectional area of 100 cm². Water is added at a constant rate of 200 mL min⁻¹ to the top of each column via a funnel. The outflow is collected in a graduated cylinder.
Question Parts
(a)
Explain how this setup allows the measurement of infiltration rate for each soil type.
(b)
If the outflow from the sand column stabilises at 150 mL min⁻¹ after the first 5 minutes, calculate the infiltration rate (in cm hr⁻¹) for the sand column.
(c)
Discuss two factors that could cause the measured infiltration rates to differ from those in the field.
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Question 3 View Details
A soil sample collected from a cultivated field has a bulk density of 1.4 g cm⁻³ and a particle density of 2.65 g cm⁻³.
Question Parts
(a)
Calculate the total porosity of the soil (express your answer as a percentage).
(b)
If field capacity is 75 % of the total porosity, determine the volumetric water content at field capacity (express as % v/v).
(c)
Discuss whether this soil is suitable for the cultivation of maize, considering its water‑holding capacity.
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Question 4 View Details
A leaf analysis of a 2‑month‑old maize crop gave the following nutrient concentrations on a dry‑weight basis: N = 2.5 %, P = 0.30 %, K = 1.20 %. The recommended optimum concentrations for a high‑yielding maize crop are N = 3.0 %, P = 0.50 %, K = 2.0 %. The topsoil (0–15 cm) has a bulk density of 1.3 g cm⁻³ and the field area is 1 ha.
Question Parts
(a)
Identify which nutrient(s) are deficient in the crop.
(b)
Assuming the farmer wishes to correct the deficiency by applying a single N‑P‑K fertilizer (15‑15‑15) uniformly over the hectare, calculate the amount of fertilizer (in kg) required to raise the deficient nutrient(s) to the recommended level. Use the following assumptions: the soil mass in the top 15 cm = bulk density × depth × area; 1 ha = 10 000 m²; 1 g cm⁻³ = 1 t m⁻³.
(c)
Briefly state two agronomic practices that could help maintain adequate nutrient levels in the long term.
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Question 5 View Details
A farmer intends to cultivate maize on 2.5 hectares of land. The recommended seed rate for the variety he will use is 25 kg ha⁻¹. Because of an anticipated 10 % loss of seed to birds, he decides to increase the seed rate by the same percentage. The soil test recommends the following fertilizer rates per hectare: nitrogen (N) = 120 kg, phosphorus as P₂O₅ = 60 kg and potassium as K₂O = 40 kg. The farmer will purchase a blended NPK fertilizer that contains 20 % N, 10 % P₂O₅ and 5 % K₂O by weight. The cost of the seed is ₦30 kg⁻¹ and the blended fertilizer costs ₦45 kg⁻¹.
Question Parts
(a)
Calculate the total quantity of seed required for the 2.5 ha farm after adjusting for the 10 % expected loss.
(b)
Determine the total weight of the blended NPK fertilizer that must be purchased to meet the recommended N, P₂O₅ and K₂O rates for the whole farm.
(c)
Compute the total cost of the seed and the blended fertilizer for the whole farm.
(d)
Briefly discuss why it is important to adjust the seed rate for expected losses and to apply a balanced NPK fertilizer in maize production.
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Question 6 View Details
A dairy farmer keeps 20 lactating cows. Each cow produces an average of 22 L of milk per day. The cows require 12 MJ of metabolizable energy (ME) for maintenance and 5 MJ of ME for each litre of milk produced. Their present total ration supplies 100 MJ of ME per cow per day. The farmer plans to supplement the diet with a concentrate feed that provides 2.5 MJ of ME per kilogram. The concentrate costs ₦120 per kilogram.
Question Parts
(a)
Calculate the total daily ME requirement per cow.
(b)
Determine the daily ME deficit that must be supplied by the concentrate feed.
(c)
Calculate the amount of concentrate feed required per cow per day (in kilograms).
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Question 7 View Details
A farmer cultivates 5 hectares of maize that has recently shown symptoms of two major insect pests: the stem borer (Busseola fusca) and the African armyworm (Spodoptera exempta). The farmer wishes to adopt an Integrated Pest Management (IPM) approach that minimises pesticide use while protecting yield.
Question Parts
(a)
Describe the complete life cycle of each pest, highlighting the stage that causes the most damage to the maize crop.
(b)
Explain two monitoring techniques that can be used to detect the onset of each pest population in the field.
(c)
Propose an IPM programme that combines cultural, biological and chemical control for each pest. Justify the choice of each control method.
(d)
If a 5 % infestation of stem borer larvae in the stand results in a 0.5 % yield loss per hectare, calculate the economic threshold (in % infestation) at which the farmer should apply chemical control, assuming the cost of control per hectare is ₦12 000 and the market price of maize is ₦30 000 per tonne with an average yield of 4 tonnes ha⁻¹.
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Question 8 View Details
A smallholder grows 200 tomato plants in a raised bed. During the rainy season, 30 plants show wilting, yellowing leaves and brown vascular streaks, while 20 other plants develop circular leaf spots with a grey‑white centre. The farmer suspects bacterial wilt and early blight respectively.
Question Parts
(a)
Identify the causal agents of the two diseases and describe the primary mode of spread for each.
(b)
Calculate the disease incidence for each disease as a percentage of the total plant population.
(c)
Discuss three cultural, two biological and one chemical control measures that could be incorporated into an integrated disease management plan for the two diseases. Explain how each measure reduces disease spread or severity.
(d)
Assuming the cost of applying the copper fungicide to the whole bed is ₦8 000 and the expected yield loss from early blight at 10 % incidence is 0.3 t ha⁻¹ (market price ₦30 000 t⁻¹), determine whether the chemical control is economically justified. Show your calculation.
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