1(a) What are the importance of soil texture in crop production? Give at least five. (5 Marks)
(b) List and explain the effects of organic matter to crops. (10 Marks)
2(a) Give reasons why weeds are difficult to control in farms. (5 Marks)
(b) List three and explain any 3 methods of controlling weeds. (10 Marks)
3(a) Illustrate the nitrogen cycle. (5 Marks)
(b) Explain the terms Ammonification; Ammonization and nitrification in relation to nitrogen cycle. (10 Marks)
4(a) Make a large labeled diagram of a typical plant cell. (5 Marks)
(b) Explain the functions of the following organelles: (i) Plastids (ii) Mitochondrion and (iii) Lysosome (10 Marks)
5(a) What are the causes of soil acidity? (5 Marks)
(b) State any four effects of soil acidity to crops. (5 Marks)
© Explain the importance of liming in agriculture. (5 Marks)
6(a) What is a nursery? (2 Marks)
(b) Mention the reasons for establishing a nursery in crop production. (4 Marks)
© With the aid of diagrams, illustrate the stages involved in budding of citrus. (9 Marks)
7(a) What is seed in agricultural term? (5 Marks)
(b) Briefly explain the different classes of seeds. (5 Marks)
© State the purpose of seed certification. (5 Marks)
8(a) Discuss the cultivation of maize under the following headings: origin, method of propagation, climatic and soil requirements, land preparation and planting and management. (6 Marks)
(b) How would you know maize plants affected by streak? (9 Marks)
Answers
Q1(a) Importance of soil texture in crop production (5)
- Determines water-holding capacity of the soil.
- Influences aeration and drainage — sandy soils drain fast, clay soils retain water/waterlog easily.
- Affects nutrient retention and availability (fine-textured soils hold more nutrients via colloids).
- Influences root penetration and growth — compact clay restricts roots, loose sand allows easy penetration.
- Determines ease of tillage/cultivation — sandy soils are easier to work than heavy clay.
- Affects soil temperature regulation.
Q1(b) Effects of organic matter on crops
- Improves soil structure – binds soil particles into aggregates, improving aeration and root penetration.
- Increases water-holding capacity – humus absorbs and retains moisture for plant use.
- Supplies plant nutrients – decomposition releases N, P, K and other minerals.
- Enhances microbial activity – serves as food/energy source for beneficial soil organisms that aid decomposition and nutrient cycling.
- Improves soil pH buffering – helps resist rapid pH changes, stabilizing nutrient availability.
- Increases Cation Exchange Capacity (CEC) – humus colloids hold nutrient cations, reducing leaching.
- Reduces soil erosion – improves aggregation, making soil more resistant to wind/water erosion.
- Darkens soil colour – increases heat absorption, warming soil for better seed germination.
Q2(a) Why weeds are difficult to control
- They produce large numbers of seeds that remain viable for many years (seed dormancy).
- Seeds are easily dispersed by wind, water, animals, and man.
- Many weeds reproduce both sexually (seeds) and vegetatively (rhizomes, tubers, stolons), so cutting alone doesn’t kill them.
- Some weeds resemble crop plants, making selective removal difficult.
- Weeds often mature and shed seeds faster than crops, replenishing the seed bank continuously.
- Some possess deep or extensive root systems that resist removal.
Q2(b) Methods of weed control (any 3, explained)
- Cultural control – practices like crop rotation, close spacing, and mulching that suppress weed growth by competition or altering conditions unfavorable to weeds.
- Mechanical/manual control – physical removal by hand-pulling, hoeing, ploughing, or slashing to uproot or cut weeds.
- Chemical control – application of herbicides (selective or non-selective) to kill weeds without (or with minimal) damage to crops.
- Biological control – use of natural enemies (insects, pathogens, or grazing animals) to reduce weed populations.
Q3(a) Nitrogen cycle (illustration description)
Atmospheric N₂ → Nitrogen fixation (by Rhizobium/Azotobacter or lightning) → Ammonia/ammonium in soil → Nitrification (Nitrosomonas converts NH₄⁺ to NO₂⁻; Nitrobacter converts NO₂⁻ to NO₃⁻) → Nitrates absorbed by plants → passed to animals through food chain → Decomposition/Ammonification of dead plants/animals and waste returns NH₃/NH₄⁺ to soil → Denitrification (denitrifying bacteria convert nitrates back to N₂ gas) → returns to atmosphere.
Q3(b) Key terms
- Ammonification: The process by which decomposer microorganisms break down nitrogen-containing organic matter (dead plants, animals, waste) to release ammonia/ammonium into the soil.
- Ammonization: Often used interchangeably with ammonification — the formation/release of ammonia compounds during decomposition of organic nitrogenous matter.
- Nitrification: The biological oxidation of ammonium (NH₄⁺) first to nitrite (NO₂⁻) by Nitrosomonas, then to nitrate (NO₃⁻) by Nitrobacter, making nitrogen available for plant uptake.
Q4(a) [Diagram: plant cell showing cell wall, cell membrane, cytoplasm, large central vacuole, nucleus (with nucleolus and nuclear membrane), chloroplasts, mitochondria, endoplasmic reticulum, Golgi body, ribosomes.]
Q4(b) Functions of organelles
- Plastids: Membrane-bound organelles involved in manufacture and storage of food; chloroplasts (contain chlorophyll) carry out photosynthesis; chromoplasts give colour to flowers/fruits; leucoplasts store starch, oils, and proteins.
- Mitochondrion: The “powerhouse” of the cell — site of aerobic respiration, producing ATP (energy) from the breakdown of glucose.
- Lysosome: Contains digestive (hydrolytic) enzymes that break down worn-out cell organelles, food particles, and foreign material; involved in intracellular digestion and cell defense.
Q5(a) Causes of soil acidity
- Leaching of basic cations (Ca, Mg, K) by heavy rainfall, leaving H⁺ ions dominant.
- Decomposition of organic matter releasing organic acids.
- Continuous use of acid-forming fertilizers (e.g., ammonium sulphate).
- Parent material naturally low in bases (e.g., derived from acidic rocks).
- Uptake of basic cations by plants without replacement.
- Acid rain from industrial/volcanic pollutants.
Q5(b) Effects of soil acidity on crops (any 4)
- Reduces availability of essential nutrients like P, Ca, Mg, and molybdenum.
- Increases toxicity of aluminium and manganese to plant roots.
- Reduces beneficial microbial activity (e.g., nitrogen-fixing bacteria).
- Stunts root growth and overall plant development.
- Lowers crop yield and quality.
Q5© Importance of liming
Liming neutralizes soil acidity by raising pH, which increases availability of nutrients (especially P, Ca, Mg), reduces aluminium/manganese toxicity, improves microbial activity (including nitrogen fixation), improves soil structure, and ultimately boosts crop yield.
Q6(a) What is a nursery?
A nursery is a piece of land or structure set aside for raising young seedlings/plants under controlled conditions before they are transplanted to the main field.
Q6(b) Reasons for establishing a nursery
- Allows close monitoring and care of delicate young seedlings.
- Economizes on seeds — fewer seeds needed compared to direct field sowing.
- Facilitates selection of only healthy, vigorous seedlings for transplanting.
- Protects young plants from pests, diseases, and adverse weather until they are strong enough for the field.
Q6© Stages in budding of citrus
- Selection of rootstock (usually 1–1.5 years old, pencil thickness) and scion (bud wood from a healthy, high-yielding mother tree).
- Making a T-shaped or inverted T-shaped incision on the rootstock bark.
- Cutting a bud (shield-shaped) from the scion with a thin sliver of bark and wood.
- Inserting the bud shield into the T-incision, ensuring cambium contact.
- Wrapping/tying firmly with budding tape, leaving the bud exposed.
- After 2–3 weeks, checking for a “take” (green, viable bud); removing the tape.
- Cutting back the rootstock above the bud union to force the bud to grow.
(A labeled diagram would show the rootstock stem, T-cut, bud shield insertion, and tape wrapping.)
Q7(a) What is seed (agricultural term)?
In agriculture, a seed is a fertilized, matured ovule of a plant, consisting of an embryo, stored food (endosperm/cotyledons), and a protective seed coat, capable of germinating into a new plant under suitable conditions.
Q7(b) Classes of seeds
- Breeder seed: The initial seed source produced by the plant breeder, of highest genetic purity.
- Foundation seed: Multiplied from breeder seed under strict supervision to maintain genetic identity.
- Certified seed: Produced from foundation seed for commercial sale to farmers; inspected and certified for quality and trueness to type.
- (Sometimes also includes Registered seed as an intermediate class between Foundation and Certified.)
Q7© Purpose of seed certification
- Ensures genetic purity and trueness to type of the variety.
- Guarantees high germination percentage and seed viability.
- Ensures seeds are free from pests, diseases, and weed contamination.
- Protects farmers from buying substandard or adulterated seeds.
- Maintains and improves crop yield and quality through reliable planting material.
Q8(a) Cultivation of maize
- Origin: Maize (Zea mays) originated in Central America (Mexico).
- Method of propagation: Propagated by seeds (sexual propagation), directly sown or dibbled.
- Climatic requirements: Warm temperatures (21–30°C), rainfall of 500–1200mm well distributed, plenty of sunshine.
- Soil requirements: Deep, fertile, well-drained loamy soil with pH 5.5–7.0.
- Land preparation and planting: Clear, plough, and harrow the land; make ridges or flat beds; plant seeds 2–3cm deep at spacing of about 75cm × 25–50cm, 2–3 seeds per hole.
- Management: Thinning, weeding, fertilizer application (especially nitrogen top-dressing), pest and disease control, and timely harvesting.
Q8(b) Identifying maize plants affected by streak
- Leaves show light-green, yellow, or white broken/continuous streaks running parallel to the veins.
- Affected plants are stunted and show poor growth.
- Leaves may become narrow and chlorotic.
- Severely affected plants produce poor, small, or no cobs.
- Symptoms are most visible on young leaves; disease is transmitted by leafhoppers (vector) and caused by maize streak virus.