neco model questions vol1 2018 agricultural_science | Practical

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Question 1 View Details
A field trial was set up to investigate the effect of intercropping maize (Zea mays) with cowpea (Vigna unguiculata) on the population of the stem borer pest (Chilo partellus). The experiment consisted of three treatments, each replicated three times (randomised complete block design). The treatments were: T1 – Sole maize T2 – Sole cowpea T3 – Maize + cowpea intercropped (1 m spacing between rows of each crop). At 45 days after planting, the number of stem borer larvae per plant was counted in each plot. The data obtained are shown in the table below: | Plot | Treatment | Larvae per plant | |------|-----------|------------------| | 1 | T1 | 12 | | 2 | T1 | 15 | | 3 | T1 | 13 | | 4 | T2 | 4 | | 5 | T2 | 5 | | 6 | T2 | 3 | | 7 | T3 | 6 | | 8 | T3 | 5 | | 9 | T3 | 7 | Using the data above, answer the following: a) Determine the mean number of larvae per plant for each treatment. b) Calculate the percentage reduction in mean larvae count of the intercropped treatment (T3) relative to the sole maize treatment (T1). c) Discuss two ecological reasons why intercropping may have reduced the stem borer population. d) Suggest one management practice that could be combined with intercropping to further suppress stem borer attacks.
Question Parts
(a)
Determine the mean number of larvae per plant for each treatment.
(b)
Calculate the percentage reduction in mean larvae count of the intercropped treatment (T3) relative to the sole maize treatment (T1).
(c)
Discuss two ecological reasons why intercropping may have reduced the stem borer population.
(d)
Suggest one management practice that could be combined with intercropping to further suppress stem borer attacks.
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Question 2 View Details
A soil sample was collected from a cultivated field and analysed for organic carbon using the Walkley‑Black dichromate oxidation method. The procedure was as follows: 1. 2.5 g of air‑dry soil was weighed into a digestion flask. 2. 10 mL of 1 N potassium dichromate (K₂Cr₂O₇) and 20 mL of concentrated sulphuric acid (H₂SO₄) were added and the mixture was heated for 30 min. 3. After cooling, the excess dichromate was titrated with 0.5 N ferrous ammonium sulphate (FAS) solution using diphenylamine as indicator. The titration data for the three replicate determinations are: | Replicate | Volume of FAS used (mL) | |-----------|--------------------------| | 1 | 12.4 | | 2 | 13.0 | | 3 | 12.7 | The correction factor for incomplete oxidation is 1.3. The soil bulk density is 1.35 g cm⁻³ and the sampled depth is 15 cm. Using the data above, answer the following: a) Calculate the average % organic carbon (C) in the soil (expressed to one decimal place). b) Determine the stock of organic carbon (in tonnes per hectare) present in the top 15 cm of the soil. c) The exchangeable bases (Ca²⁺, Mg²⁺, K⁺, Na⁺) in the same soil were found to be 12, 5, 2 and 1 cmol kg⁻¹ respectively. Compute the Cation Exchange Capacity (CEC) in cmol kg⁻¹ and comment on the fertility implication of the obtained CEC value. d) Identify two sources of error that could affect the accuracy of the Walkley‑Black determination and suggest a way to minimise each error.
Question Parts
(a)
Calculate the average % organic carbon (C) in the soil (expressed to one decimal place).
(b)
Determine the stock of organic carbon (in tonnes per hectare) present in the top 15 cm of the soil.
(c)
The exchangeable bases (Ca²⁺, Mg²⁺, K⁺, Na⁺) in the same soil were found to be 12, 5, 2 and 1 cmol kg⁻¹ respectively. Compute the Cation Exchange Capacity (CEC) in cmol kg⁻¹ and comment on the fertility implication of the obtained CEC value.
(d)
Identify two sources of error that could affect the accuracy of the Walkley‑Black determination and suggest a way to minimise each error.
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Question 3 View Details
A farmer wishes to compare the efficiency of two hand tools for weeding a uniform field. The tools are: 1. A traditional hand hoe. 2. A newly introduced ergonomic hand hoe. The farmer selects a 0.5 ha (5,000 m²) plot where the weed density is known to be 150 weeds per 100 m². For each tool, the farmer clears a 10 m × 10 m quadrat (100 m²) and records the time taken and the number of weeds removed. The recorded data are: | Tool | Time taken (minutes) | Weeds removed | |---------------------|----------------------|---------------| | Traditional hand hoe| 12 | 150 | | Ergonomic hand hoe | 9 | 150 | Using this information, answer the following questions:
Question Parts
(a)
Calculate the work output of each tool expressed as the number of weeds removed per minute.
(b)
Estimate the total time required to clear the whole 0.5 ha plot with each tool, assuming the weed density is uniform throughout the field.
(c)
Calculate the percentage time saved when the ergonomic hand hoe is used instead of the traditional hand hoe.
(d)
Identify two possible sources of error in this experiment and suggest one precaution for each to improve reliability.
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Question 4 View Details
A small 15 kW tractor is used to pull a two‑bottom disc plough through a loamy field. The tractor speed is kept constant at 5 km h⁻¹. A drawbar dynamometer records the draft force required at three different ploughshare depths as shown below. | Depth of ploughshare (cm) | Draft force (kN) | |---------------------------|------------------| | 10 | 2.8 | | 15 | 3.9 | | 20 | 5.1 | Assume that the relationship between draft force (F) and depth (d) is linear. Answer the following questions:
Question Parts
(a)
Derive the linear equation that relates draft force (kN) to ploughshare depth (cm).
(b)
Using the equation from part (a), estimate the draft force when the ploughshare depth is 12 cm.
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