neco 2020 agricultural_science | Practical

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Question 1 View Details
A field experiment was set up to compare a monoculture of maize with an intercropping system of maize and cowpea. Two adjacent plots of equal size (20 m × 20 m) were prepared. Soil moisture (as % volume) and weed density (number of weeds per m²) were recorded weekly for four weeks. The data obtained are shown in the table below. | Week | Monocrop Soil Moisture (%) | Intercrop Soil Moisture (%) | Monocrop Weed Density (per m²) | Intercrop Weed Density (per m²) | |------|----------------------------|-----------------------------|--------------------------------|---------------------------------| | 1 | 22 | 24 | 15 | 9 | | 2 | 20 | 23 | 14 | 8 | | 3 | 19 | 22 | 13 | 7 | | 4 | 18 | 21 | 12 | 6 | Using the above information, answer the following questions:
Question Parts
(a)
Calculate the average soil moisture for the monocrop plot and for the intercropped plot over the four‑week period.
(b)
Determine the percentage reduction in average weed density in the intercropped plot compared with the monocrop plot.
(c)
Based on the results obtained, state which cropping system is more sustainable and give two reasons supporting your choice.
(d)
Mention two possible sources of error in this experiment and two precautions that could minimise them.
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Question 2 View Details
A soil sample was collected from a field to determine its water‑holding characteristics using the gravimetric method. The following measurements were recorded: - Dry weight of the soil sample (after oven‑drying at 105 °C) = 200 g - Weight of the sample when saturated with water (no air voids) = 340 g - Weight of the sample after free drainage for 2 hours (field capacity) = 260 g - Weight of the sample after allowing it to dry to the permanent wilting point = 220 g - Bulk density of the soil = 1.3 g cm⁻³ - Depth of the effective root zone for the crop = 60 cm Using the data above, answer the following questions:
Question Parts
(a)
Calculate the gravimetric water content (expressed as % w/w) at field capacity and at the wilting point.
(b)
Convert the gravimetric water contents obtained in part (a) to volumetric water contents (expressed as % v/v). Use the bulk density provided (assume water density = 1 g cm⁻³).
(c)
Calculate the Available Water Capacity (AWC) of the soil in the root zone, expressed in millimetres (mm).
(d)
A crop to be cultivated on the field requires a total water supply of 150 mm during the growing season. Based on the AWC calculated in part (c), state whether the soil can meet the crop’s water requirement and justify your answer.
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Question 3 View Details
A farmer who is 165 cm tall wants to select a hand hoe. The recommended handle length for a farmer is 0.75 times the farmer's height. The farmer has three hand hoe handles available with lengths of 110 cm, 120 cm and 130 cm. The farmer will only accept a handle whose length is within ±5 cm of the recommended length. To decide which handle is best, the farmer measures the time taken to till a 0.5 ha plot with each handle and records the following times: - 110 cm handle: 45 minutes - 120 cm handle: 38 minutes - 130 cm handle: 42 minutes Using this information, answer the questions below.
Question Parts
(a)
Calculate the recommended handle length for the farmer.
(b)
State which of the available handles satisfy the length requirement.
(c)
From the handles that meet the length criterion, which one gives the least tilling time?
(d)
Calculate the percentage reduction in tilling time of the chosen handle (from part c) compared with the longest time recorded among all three handles.
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Question 4 View Details
A farmer owns a 30 HP tractor whose engine speed can be varied between 1,200 rpm and 2,400 rpm. The tractor’s power‑take‑off (PTO) shaft is driven by a belt system with a pulley ratio of 3:1 (engine pulley : PTO pulley) and the belt has an overall efficiency of 90%. The threshing machine to be used requires a PTO speed of exactly 540 rpm and a minimum torque of 250 Nm. Using the information given, determine whether the tractor can meet the required speed and torque. If the tractor cannot meet the torque requirement at the required speed, calculate the minimum engine speed needed (still within the adjustable range) to satisfy both conditions. Finally, suggest two practical adjustments the farmer could make to increase the available PTO torque.
Question Parts
(a)
Calculate the torque that will be available at the PTO when the engine is running at its minimum speed of 1,200 rpm.
(b)
State whether the torque obtained in part (a) satisfies the threshing machine’s minimum requirement of 250 Nm.
(c)
If the required PTO speed of 540 rpm must also be met, calculate the minimum engine speed (within the adjustable range) that will give both the correct speed and at least the required torque.
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