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BGCSE Agricultural Science 1517 study materials
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BGCSE Agricultural Science 1517 practice questions

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Question 1Soil Science and Soil Management

Which term describes the relative proportions of sand, silt and clay particles in a soil?

  1. Soil texture Correct answer.
  2. Soil porosity
  3. Soil structure
  4. Soil colour

Explanation

Soil texture is the relative proportion of sand, silt and clay particles in a soil. It controls how the soil feels and how water moves through it. Soil structure, by contrast, describes how particles are grouped into aggregates.

Question 2Soil Science and Soil Management

In a typical soil profile, which horizon is the main zone of accumulated organic matter and plant roots?

  1. R horizon
  2. C horizon
  3. B horizon
  4. A horizon Correct answer.

Explanation

The A horizon is the topsoil, where organic matter accumulates and most plant roots are concentrated. It is usually darker and more biologically active than deeper layers. The B and C horizons lie below it, and the R horizon is bedrock.

Question 3Soil Science and Soil Management

Which benefit of soil organic matter most directly increases the amount of water a sandy soil can hold?

  1. It changes soil colour
  2. It lowers soil pH sharply
  3. It raises cation exchange capacity
  4. It increases water retention Correct answer.

Explanation

Organic matter acts like a sponge and holds water that plants can later use. This effect is especially valuable in sandy soils, which drain quickly and store little water. The other listed effects do not directly increase water storage.

Question 4Soil Science and Soil Management

A soil test reports pH 5.2 and the crop to be grown prefers pH 6.5. Which practice is most appropriate?

  1. Apply elemental sulfur
  2. Apply agricultural lime and retest Correct answer.
  3. Flood the field with saline water
  4. Apply gypsum to the soil

Explanation

Agricultural lime raises soil pH by neutralising acidity, so it is the appropriate treatment for a soil that is too acidic for the crop. Elemental sulfur has the opposite effect and lowers pH. Gypsum supplies calcium and sulfur but does not reliably correct acidity, and saline water would worsen soil conditions.

Question 5Soil Science and Soil Management

A farmer on a gentle slope wants to reduce soil erosion between rows of maize. Which practice is most suitable?

  1. Leave the soil bare between the crop rows
  2. Remove crop residues after harvest
  3. Sow a cover crop between rows Correct answer.
  4. Plough up and down the slope

Explanation

A cover crop protects the soil surface from raindrop impact and slows runoff between maize rows. Removing residues leaves the soil bare, and ploughing up and down the slope channels water downhill and accelerates erosion. Bare soil between rows is also exposed to erosive forces.

Question 6Soil Science and Soil Management

A soil is at field capacity. What does this mean for water movement and plant availability?

  1. All water has been lost beyond wilting point
  2. The soil is saturated and water drains freely
  3. Gravitational water has drained and capillary water remains Correct answer.
  4. Only hygroscopic water remains in the soil

Explanation

At field capacity, the soil has drained free gravitational water, but capillary water is still held in the smaller pores. This capillary water is the main reserve that plant roots can absorb. Saturation, wilting point and hygroscopic water describe wetter or drier states.

Question 7Soil Science and Soil Management

Which change is most likely to increase soil compaction on a cultivated field?

  1. Adding compost to the topsoil
  2. Growing deep-rooted cover crops
  3. Trafficking wet soil with heavy machinery Correct answer.
  4. Using wider tyres that reduce ground pressure

Explanation

Wet soil is weak and compacts readily under the weight of machinery or livestock. Wider tyres, organic matter and deep roots tend to reduce compaction or improve soil strength. Trafficking wet soil therefore increases the risk of compacted layers.

Question 8Soil Science and Soil Management

Two soils have similar pH. Soil X contains 35% clay and 4% organic matter; Soil Y contains 10% clay and 1% organic matter. Which statement best explains their likely difference in cation exchange capacity?

  1. Soil X has more exchange sites from clay and humus Correct answer.
  2. Soil Y has more exchange sites from sand
  3. Both soils have equal CEC because pH is the same
  4. Soil X has fewer exchange sites from clay

Explanation

Clay particles and organic matter carry negative charges that hold exchangeable cations. Soil X has much more clay and organic matter than Soil Y, so it should have a higher cation exchange capacity. Equal pH does not make CEC equal, and sand contributes very little to CEC.

Question 9Soil Science and Soil Management

A farmer irrigates with slightly saline water. Which management practice best reduces salt accumulation in the root zone?

  1. Leach salts with adequate drainage Correct answer.
  2. Add gypsum without testing the soil
  3. Apply less water to concentrate salts
  4. Cover the soil to trap salts

Explanation

Salts accumulate in the root zone when evaporation exceeds leaching. Applying extra water moves salts downward, but good drainage is essential so they are removed from the profile. Using less water concentrates salts, and gypsum is not a universal remedy for salinity.

Question 10Soil Science and Soil Management

A crop needs phosphorus, which moves very little in soil. Which placement method is most efficient?

  1. Apply it to the leaves as a gas
  2. Band it near the seed or roots Correct answer.
  3. Place it deep below the root zone
  4. Broadcast it on the surface and leave it

Explanation

Phosphorus is largely immobile in soil, so roots must grow to the fertilizer to absorb it. Banding places phosphorus close to developing roots, improving uptake efficiency. Broadcasting leaves much of it away from roots, and deep placement below the root zone makes it unavailable.

Question 11Soil Science and Soil Management

Which term describes the arrangement of soil particles into aggregates such as granules, blocks and plates?

  1. Soil texture
  2. Soil consistence
  3. Soil structure Correct answer.
  4. Soil porosity

Explanation

Soil structure is the way individual particles are grouped into aggregates, and it controls pore shape and root penetration. Texture, by contrast, refers only to the proportions of sand, silt and clay. Consistence describes how soil behaves when pressed or worked, while porosity is the amount of pore space.

Question 12Soil Science and Soil Management

Which type of soil water is held so tightly by soil particles that plant roots cannot absorb it?

  1. Drainage water
  2. Hygroscopic water Correct answer.
  3. Gravitational water
  4. Capillary water

Explanation

Hygroscopic water forms a very thin film held by strong adhesive forces around soil particles and is unavailable to plants. Capillary water is held in smaller pores and is the main plant-available supply. Gravitational water drains freely through large pores after rain.

Question 13Soil Science and Soil Management

Which soil organism is best known for burrowing through soil and improving aeration and water movement?

  1. Fungi
  2. Earthworms Correct answer.
  3. Nematodes
  4. Bacteria

Explanation

Earthworms create burrows and castings that increase pore space, mix organic matter with mineral soil and improve water infiltration. Bacteria and fungi are mainly decomposers, and nematodes are mostly microscopic worms living in soil water films.

Question 14Soil Science and Soil Management

Which practice is most likely to increase the cation exchange capacity of a sandy soil over several years?

  1. Deep ploughing
  2. Incorporating compost Correct answer.
  3. Applying gypsum
  4. Applying elemental sulfur

Explanation

Cation exchange capacity rises mainly with increases in clay and organic matter, and compost adds stable organic matter with many negatively charged exchange sites. Gypsum supplies calcium but does not greatly increase exchange capacity. Sulfur acidifies soil, and deep ploughing dilutes organic matter.

Question 15Soil Science and Soil Management

Soil A has many fine pores, while Soil B has many large pores. Which statement about water retention is most likely correct?

  1. Soil A retains more water Correct answer.
  2. Soil B retains more water
  3. Soil A has lower total porosity
  4. Both soils retain equal water

Explanation

Fine pores hold water strongly by capillary forces, so a soil dominated by fine pores retains more water after free drainage. Large pores drain quickly and mainly allow air movement. Total porosity depends on bulk density and particle arrangement, not on pore size alone.

Question 16Soil Science and Soil Management

Which process is the main way that wind transports medium sand-sized particles across a bare field?

  1. Solution
  2. Surface creep
  3. Suspension
  4. Saltation Correct answer.

Explanation

Saltation is the bouncing or hopping movement of medium sand grains lifted by wind and dropped back to the surface. Suspension carries very fine particles such as silt and clay high in the air. Surface creep moves larger grains by rolling or pushing, and solution applies to dissolved substances.

Question 17Soil Science and Soil Management

A calcareous soil has a pH of 7.8. Which micronutrient is most likely to be deficient because of low solubility at this pH?

  1. Chloride
  2. Iron Correct answer.
  3. Molybdenum
  4. Boron

Explanation

Iron solubility falls sharply as pH rises, so iron deficiency is common on calcareous or alkaline soils. Molybdenum availability generally increases at high pH, and chloride is not strongly reduced by alkalinity. Boron availability can be affected by pH, but iron is the classic micronutrient tied to high-pH chlorosis.

Question 18Soil Science and Soil Management

A soil sample has an oven-dry mass of 120 g and a bulk volume of 100 cm³. What is its bulk density?

  1. 1.45 g/cm³
  2. 2.20 g/cm³
  3. 1.20 g/cm³ Correct answer.
  4. 0.83 g/cm³

Explanation

Bulk density equals oven-dry mass divided by bulk volume, so 120 g ÷ 100 cm³ = 1.20 g/cm³. Bulk volume includes both solids and pore space. The value 0.83 would result from dividing volume by mass, which is not the formula.

Question 19Soil Science and Soil Management

A soil contains 45% sand, 30% silt and 25% clay. Which textural class is most likely?

  1. Silt loam
  2. Sandy loam
  3. Clay loam
  4. Loam Correct answer.

Explanation

A loam generally has roughly balanced sand, silt and clay, within about 23–52% sand, 28–50% silt and 7–27% clay. The given percentages fall inside those ranges. Sandy loam has more sand, silt loam has much more silt, and clay loam has more clay.

Question 20Soil Science and Soil Management

A field remains waterlogged for several weeks. Which change is most likely in the soil?

  1. Organic matter decays faster
  2. Ferric iron increases
  3. Ferrous iron accumulates Correct answer.
  4. Nitrate levels rise

Explanation

Waterlogging removes oxygen, so soil microbes use alternative electron acceptors and reduced compounds such as ferrous iron accumulate. Nitrate is also lost through denitrification, and organic matter decomposition slows under anaerobic conditions. Ferric iron is reduced rather than increased.

Question 21Soil Science and Soil Management

Which term describes the downward movement of dissolved nutrients and salts through the soil profile?

  1. Leaching Correct answer.
  2. Erosion
  3. Capillary rise
  4. Denitrification

Explanation

Leaching is the downward movement of dissolved salts and nutrients carried by water percolating through the profile. It removes soluble material from the root zone rather than transporting soil particles sideways. Erosion, capillary rise and denitrification describe different processes.

Question 22Soil Science and Soil Management

A soil has a bulk density of 1.5 g/cm³ and a particle density of 2.5 g/cm³. What is its total porosity?

  1. 60%
  2. 20%
  3. 80%
  4. 40% Correct answer.

Explanation

Total porosity is calculated as 1 minus the ratio of bulk density to particle density. Here 1.5 divided by 2.5 equals 0.60, so porosity is 1 minus 0.60, or 40 percent. This represents the fraction of soil volume occupied by pores.

Question 23Soil Science and Soil Management

In a dry season, which practice most directly reduces water loss from the soil surface by evaporation?

  1. Removing crop residues
  2. Applying a surface mulch Correct answer.
  3. Increasing row spacing
  4. Deep ploughing

Explanation

A surface mulch shades the soil, lowers its temperature and slows the evaporative demand at the surface. This keeps more water in the root zone during a dry period. Deep ploughing, wider rows and residue removal do not provide this protective cover.

Question 24Soil Science and Soil Management

A soil has pH 8.5, a high exchangeable sodium percentage and a dispersed surface crust. Which management practice is most appropriate?

  1. Cultivate the surface while it is wet
  2. Apply gypsum and leach with clean water Correct answer.
  3. Apply ground limestone and incorporate it
  4. Irrigate with saline water more frequently

Explanation

A high exchangeable sodium percentage, alkaline pH and dispersed aggregates are classic signs of a sodic soil. Gypsum supplies calcium that displaces sodium, and leaching with good-quality water carries the sodium below the root zone. Lime does not correct sodicity and may raise pH further.

Question 25Crop Production and Agronomy

Which set of conditions is essential for the germination of most crop seeds?

  1. Pesticide, mulch and shade
  2. Nitrogen, phosphorus and potassium
  3. Water, oxygen and a suitable temperature Correct answer.
  4. Light, carbon dioxide and soil minerals

Explanation

Most crop seeds germinate when they absorb water, receive oxygen for respiration and are held at a suitable temperature. These three conditions activate enzymes and support the growing embryo; light and soil minerals are not the primary triggers.

Question 26Crop Production and Agronomy

A soil test shows a pH of 5.2. Which action is most appropriate for a maize crop that prefers pH 5.8–7.0?

  1. Apply elemental sulfur to raise the pH
  2. Apply gypsum to lower the pH further
  3. Apply agricultural lime to raise the pH Correct answer.
  4. Flood the field to leach the acidity

Explanation

A pH of 5.2 is below the preferred range for maize, so the soil is too acidic. Agricultural lime neutralises soil acidity and raises pH, improving nutrient availability. Gypsum supplies calcium without changing pH much, sulfur lowers pH, and flooding is not a practical correction.

Question 27Crop Production and Agronomy

A seedling emerges with two cotyledons and net-like leaf veins. To which group does the plant most likely belong?

  1. Fern
  2. Monocot
  3. Dicot Correct answer.
  4. Gymnosperm

Explanation

Plants with two cotyledons and net-like leaf veins are dicotyledons. Monocots have a single cotyledon and parallel veins, gymnosperms produce naked seeds, and ferns reproduce by spores rather than seeds.

Question 28Crop Production and Agronomy

A farmer alternates maize with groundnuts. Which benefit best explains this rotation?

  1. Groundnuts shade the maize from strong sunlight
  2. Maize residues supply nitrogen to the groundnuts
  3. Groundnuts release a toxin that kills maize pests
  4. Groundnuts fix nitrogen in root nodules Correct answer.

Explanation

Groundnut is a legume that forms root nodules containing rhizobia, which fix atmospheric nitrogen into forms the plant and following crop can use. Rotating a cereal with such a legume improves soil nitrogen and breaks pest cycles.

Question 29Crop Production and Agronomy

When transplanting tomato seedlings, which practice gives the best chance of establishment?

  1. Plant deeper than in the nursery and firm the soil Correct answer.
  2. Water only after a week to encourage deep roots
  3. Pull seedlings by the stem and shake off soil
  4. Transplant at midday in full sun to dry leaves

Explanation

Tomato seedlings establish best when planted slightly deeper than in the nursery and the soil is firmed around the roots. This improves root-soil contact and support, and watering immediately reduces transplant shock and wilting.

Question 30Crop Production and Agronomy

In a dry region with scarce water, which irrigation method usually delivers water most efficiently to crop roots?

  1. Overhead sprinklers in strong wind
  2. Flood irrigation of the whole field
  3. Drip irrigation through perforated tubes Correct answer.
  4. Furrow irrigation with long unlined channels

Explanation

Drip irrigation delivers water slowly and directly to the root zone through perforated tubes, minimising evaporation, runoff and deep percolation. In dry areas with scarce water, these savings make it more efficient than flood, furrow or overhead sprinkler systems.

Question 31Crop Production and Agronomy

A crop has luxuriant dark green leaves but weak, lodging stems and delayed maturity. Which nutrient is most likely excessive?

  1. Potassium
  2. Phosphorus
  3. Calcium
  4. Nitrogen Correct answer.

Explanation

Excess nitrogen encourages vigorous vegetative growth, producing dark green, succulent leaves and weak stems that lodge easily. It also delays maturity. Phosphorus, potassium and calcium do not normally cause these symptoms when excessive.

Question 32Crop Production and Agronomy

Maize is planted at 75 cm between rows and 25 cm within rows. If the field is 100 m by 100 m, what is the approximate plant population?

  1. About 53,333 plants Correct answer.
  2. About 13,333 plants
  3. About 5,333 plants
  4. About 26,667 plants

Explanation

Convert spacing to metres: 0.75 m between rows and 0.25 m within rows gives 0.1875 m² per plant. A 100 m by 100 m field is 10,000 m², so divide 10,000 by 0.1875 to obtain about 53,333 plants.

Question 33Crop Production and Agronomy

A maize variety yields 8 t/ha at a research station but only 3 t/ha on a nearby farm with the same seed and fertilizer. Soil tests show adequate nutrients, but the farm has heavy clay that waterlogs after rain. Which factor most likely explains the yield gap?

  1. Fertilizer being applied too evenly
  2. Seed variety being too improved
  3. Poor soil drainage limiting root function Correct answer.
  4. Too much sunlight damaging the leaves

Explanation

Waterlogging fills soil pores with water and reduces oxygen available to roots, impairing respiration, water uptake and nutrient absorption. Even with adequate nutrients and good seed, this root-zone limitation can explain a large yield gap.

Question 34Crop Production and Agronomy

Which statement best describes the critical period for weed control in an annual field crop?

  1. The crop is most sensitive to weed competition during early growth Correct answer.
  2. Weeds may be left until harvest because they do not compete
  3. Weeds should be removed only after the crop flowers
  4. Weed competition matters only in the nursery

Explanation

The critical period is the growth stage when weeds compete most strongly with the crop, usually early in the season. Young crop plants are small and lose light, water and nutrients to fast-growing weeds, so early control protects yield.

Question 35Crop Production and Agronomy

Which seedbed condition is most important when sowing small seeds such as lettuce?

  1. A loose, cloddy surface with deep cracks
  2. A dry surface layer covered with coarse trash
  3. A compacted pan about ten centimetres below the surface
  4. A fine, firm, level tilth with adequate moisture Correct answer.

Explanation

Small seeds have limited stored reserves and must be sown shallow, so the bed should be fine, firm and level. Good seed-to-soil contact keeps sowing depth uniform and holds moisture around the seed, giving even germination and a strong, even stand.

Question 36Crop Production and Agronomy

A farmer sows maize seed 12 cm deep in moist clay loam. What is the most likely result?

  1. Stronger anchorage with no effect on emergence
  2. Faster germination because deeper soil stays cooler and wetter
  3. Earlier flowering because the shoot is shortened
  4. Poor emergence from exhausted seed reserves Correct answer.

Explanation

Maize is normally sown about four to six centimetres deep. At twelve centimetres the young shoot must grow much further before reaching the surface, using up the limited food in the endosperm, so many seedlings die before emergence and the stand is thin and uneven.

Question 37Crop Production and Agronomy

Which change is the most reliable sign that maize grown for grain has reached harvest maturity?

  1. Leaves turn yellow about two weeks after tasselling
  2. A black layer forms at the base of the kernel Correct answer.
  3. The cob stands upright above the leaves
  4. Silks appear at the top of the cob

Explanation

At physiological maturity a dark abscission layer, often called the black layer, forms where the kernel joins the cob. This shows that dry matter accumulation has stopped and the grain can be harvested and dried safely with little loss of quality or yield.

Question 38Crop Production and Agronomy

A maize crop at the six-leaf stage needs a nitrogen top dressing. Which method places the fertilizer where roots can use it while limiting leaf scorch?

  1. Broadcast urea onto the leaves at midday
  2. Dissolve the fertilizer and spray it over the whole field
  3. Band it 10–15 cm beside the rows and cover lightly Correct answer.
  4. Place prills in a band directly against the stem base

Explanation

A nitrogen top dressing works best when banded beside the row, away from the stem, and lightly covered. This places the nutrient in the moist root zone, reduces losses by volatilisation and avoids the direct contact with foliage and stems that causes scorching.

Question 39Crop Production and Agronomy

A farmer can irrigate only once a week. Which practice best reduces water loss from the soil surface between irrigations?

  1. Cultivate the soil into a fine dust mulch every day
  2. Apply a straw mulch over the soil surface Correct answer.
  3. Increase the spacing between plants
  4. Irrigate in the afternoon at the hottest time

Explanation

A straw mulch shades the soil, lowers its surface temperature and slows evaporation, so more of the water stored after each irrigation remains available to the roots. It also reduces crusting and protects the surface from the impact of rain or overhead watering.

Question 40Crop Production and Agronomy

Cowpea is to be intercropped with maize. Which arrangement is likely to use light best and reduce competition between the two crops?

  1. Mix both seeds and broadcast them thickly over the plot
  2. Plant cowpea in alternate rows with a shorter maize variety Correct answer.
  3. Plant cowpea beneath a very tall maize canopy at high density
  4. Plant cowpea in the same hill as the maize

Explanation

Alternate rows and a shorter maize canopy reduce shading of the legume, so the two crops intercept light at different heights instead of competing for the same layer. This arrangement also spreads root competition and makes weeding, spraying and harvesting easier.

Question 41Crop Production and Agronomy

Which storage condition most encourages insect damage and mould in stored grain?

  1. Damp grain heaped in a warm room Correct answer.
  2. Dry grain stored on a raised platform
  3. Cool, dry grain kept in sealed bags
  4. Clean grain treated and kept in closed containers

Explanation

Storage insects and moulds multiply fastest when grain is damp and warm. Damp grain heaped in a warm room heats up, supports fungal growth and allows weevils to breed rapidly, leading to caking, discolouration and serious losses.

Question 42Crop Production and Agronomy

Older lower leaves of a tomato crop show yellowing between the veins while the veins stay green, and the problem appears first on old leaves. Which nutrient is most likely deficient?

  1. Magnesium Correct answer.
  2. Calcium
  3. Iron
  4. Nitrogen

Explanation

Magnesium is mobile within the plant, so when supply is short it is moved from older leaves to young growing tissue. The older leaves then develop interveinal chlorosis while the veins remain green, and the problem spreads upwards as the shortage continues.

Question 43Crop Production and Agronomy

A maize field wilts at midday even though soil at 30 cm depth is moist. Which explanation is most likely?

  1. Transpiration exceeds uptake, so stomata close to conserve water Correct answer.
  2. Nutrient uptake has stopped for the day
  3. The plants have already completed grain filling
  4. The roots have permanently stopped absorbing water

Explanation

Midday wilting with moist subsoil usually reflects a temporary imbalance: high evaporative demand makes leaves lose water faster than roots can replace it, so stomata close and the leaves droop. The plants normally recover in the evening, unlike plants suffering permanent wilting.

Question 44Crop Production and Agronomy

A cabbage grower wants to limit aphid damage with as little pesticide as possible. Which approach is the soundest integrated pest management strategy?

  1. Apply extra nitrogen so the plants outgrow the aphids
  2. Remove all weeds and hedgerows around the field
  3. Monitor weekly, conserve ladybirds and parasitic wasps, spray only above a threshold Correct answer.
  4. Spray a broad-spectrum insecticide every week regardless of pest numbers

Explanation

Integrated pest management relies on regular scouting, action thresholds and biological control before chemicals are used. Counting aphids and natural enemies weekly allows sprays to be timed only when the pest is actually causing economic damage, which saves money and slows resistance.

Question 45Crop Production and Agronomy

A lot of 200 maize seeds is tested in a germination tray, and 170 normal seedlings emerge. How should this result be used when deciding the sowing rate?

  1. Viability is 85%, so the sowing rate must be increased. Correct answer.
  2. Viability is 17%, so the seed lot should be discarded as worthless.
  3. Viability is 100%, because only healthy seedlings were counted.
  4. Viability is 85%, so the normal sowing rate can be reduced by 15%.

Explanation

Germination percentage is calculated as 170 divided by 200, multiplied by 100, giving 85%. A seed lot with less than full viability must be sown more thickly so that the target plant population is still reached. The required pure-live-seed rate is divided by 0.85 to find the actual sowing rate.

Question 46Crop Production and Agronomy

Which statement best describes the main purpose of primary tillage when preparing land for an annual crop?

  1. To loosen soil and bury weeds and residues Correct answer.
  2. To apply a selective herbicide evenly across the field
  3. To firm the seedbed before sowing the crop
  4. To grade the field for surface irrigation

Explanation

Primary tillage, such as ploughing, opens and aerates compacted soil and buries weeds, crop residues and organic matter. It creates the rough basis that secondary tillage later refines into a seedbed. Herbicide application and land grading are separate operations, not the purpose of primary tillage.

Question 47Crop Production and Agronomy

Cassava is normally propagated by which method?

  1. Planting mature stem cuttings Correct answer.
  2. Budding onto a maize stem
  3. Rooting leaf petioles in water
  4. Sowing fresh botanical seed each season

Explanation

Cassava is propagated vegetatively from mature stem cuttings, usually 20 to 30 cm long, each carrying several nodes. These cuttings root and sprout to form a new plant that is genetically identical to the parent. Botanical seed is used mainly by plant breeders, not for normal field planting.

Question 48Crop Production and Agronomy

A gardener wants a compost heap to heat up quickly. Which material should be added as the main nitrogen-rich green component?

  1. Dry maize stover
  2. Sawdust
  3. Fresh poultry litter Correct answer.
  4. Chopped dry banana leaves

Explanation

Fresh poultry litter is rich in nitrogen and has a low carbon-to-nitrogen ratio, so it is a green material that fuels rapid microbial growth and heating. Dry stover, sawdust and dry banana leaves are browns with high carbon-to-nitrogen ratios and decompose slowly. A compost heap heats best when greens and browns are mixed in reasonable balance.

Question 49Crop Production and Agronomy

A recommendation is 60 kg of nitrogen per hectare. How much urea, which contains 46% nitrogen, must be applied per hectare?

  1. About 276 kg
  2. About 28 kg
  3. About 60 kg
  4. About 130 kg Correct answer.

Explanation

The amount of fertilizer needed is the recommended nutrient divided by the nutrient concentration in the product. Dividing 60 kg by 0.46 gives about 130 kg of urea per hectare. Multiplying instead of dividing would underestimate the fertilizer requirement.

Question 50Crop Production and Agronomy

A maize field is heavily infested with broad-leaved weeds while the maize is at the four-leaf stage. Which herbicide type is most suitable?

  1. A soil sterilant applied to the whole field
  2. A non-selective contact herbicide sprayed over all plants
  3. A selective broad-leaved weed herbicide Correct answer.
  4. A pre-planting soil fumigant

Explanation

A selective herbicide can remove broad-leaved weeds from a grass crop such as maize with limited injury to the crop when applied at the correct stage and dose. The product label must be followed because crop stage and weed size affect safety and effectiveness. Non-selective products would also damage the maize.