WAEC SSCE - Agricultural Science - 1995 (Essay)

Answer Details

The nitrogen cycle is a natural process that involves the transformation of nitrogen from one form to another. Nitrogen is a crucial element required for the growth and development of plants and other living organisms. However, nitrogen in its gaseous form (N₂) cannot be used by plants directly. Therefore, it has to be converted into other forms such as ammonia, nitrate, and nitrite, which plants can absorb and use.

The nitrogen cycle can be divided into several steps:

1. Nitrogen Fixation: The first step in the nitrogen cycle is nitrogen fixation. Nitrogen gas (N₂) is converted into ammonia (NH₃) by nitrogen-fixing bacteria such as Rhizobium found in the root nodules of legumes like beans and peas. Some free-living bacteria like Azotobacter and Clostridium also fix atmospheric nitrogen.
2. Nitrification: The next step is nitrification, where ammonia (NH₃) is converted into nitrite (NO₂^-) and then into nitrate (NO₃^-) by nitrifying bacteria. Nitrate is the form of nitrogen that is most commonly taken up by plants.
3. Assimilation: Assimilation is the process by which plants and animals absorb nitrogen in the form of ammonia, nitrate, and other nitrogen compounds to synthesize amino acids, proteins, and other nitrogen-containing organic molecules.
4. Ammonification: Ammonification is the process by which decomposers like bacteria and fungi break down nitrogen-containing organic matter such as dead plants and animals and release ammonia into the soil.
5. Denitrification: Denitrification is the final step in the nitrogen cycle, where nitrate (NO₃^-) is converted back into gaseous nitrogen (N₂) by denitrifying bacteria under anaerobic conditions in soil and water.

Here is a labelled diagram of the nitrogen cycle:

            Nitrogen Fixation
                N2 + 3H2 -> 2NH3

                        NH3
                         |
                     Nitrification
                    NH3 -> NO2- -> NO3-

                    Assimilation
                         |
                    NH3, NO3-
                         |
                    Amino acids, proteins, etc.

                 Ammonification
                      Organic nitrogen
                          |
                          NH3

                 Denitrification
                        NO3-
                         |
                NO2-, NO, N2O, N2
                         |
                         N2

Overall, the nitrogen cycle is an essential process that enables the conversion of atmospheric nitrogen into forms that

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(a) Ten tools or equipment used on a dairy cattle farm:

1. Milking machine
2. Milking pails/buckets
3. Milk churns / milk cans
4. Milk strainer or sieve (filter)
5. Milk cooler / refrigerator
6. Lactometer (for testing milk quality/density)
7. Cream separator
8. Weighing scale (or milk-measuring cans)
9. Wheelbarrow (for feed and dung) and feeding troughs
10. Water troughs and hose/hoses; disinfectant and udder-washing cloths/towels

(b) Three harmful contaminants of milk:

1. Disease-causing micro-organisms (bacteria) such as those causing tuberculosis and brucellosis.
2. Dirt and dust (soil, dung, hair) falling into the milk.
3. Chemical residues such as antibiotic and drug residues (or traces of detergents and disinfectants).

(c) Three precautions to obtain clean milk:

1. Clean the animal and the udder: wash and dry the cow's udder and teats with a clean cloth and mild antiseptic before milking, and keep the animal and its surroundings clean, so that dirt and germs do not fall into the milk.
2. Use clean, sterilised utensils and clean hands: all pails, churns and the milking machine must be thoroughly washed, sterilised and dried, and the milker's hands must be clean and healthy, to prevent contamination.
3. Handle and store milk hygienically: strain the milk immediately after milking and cool it quickly to a low temperature in a covered container, keeping it away from dust and flies, to check the growth of bacteria.

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(a) Six problems of agricultural development in Nigeria:

1. Inadequate finance and poor access to credit facilities by farmers.
2. Poor storage and processing facilities, leading to heavy post-harvest losses.
3. Poor transportation network and bad rural roads.
4. Use of crude and outdated farm implements with low mechanisation.
5. Land tenure system that fragments land and discourages large-scale farming.
6. Inadequate and inefficient agricultural extension services.

(b) Five possible solutions:

1. Provide soft loans and agricultural credit to farmers through banks and cooperatives.
2. Establish modern storage and processing facilities such as silos and cold rooms.
3. Construct and maintain good rural roads and provide affordable transport.
4. Encourage mechanisation by subsidising tractors and modern implements.
5. Reform the land tenure system and strengthen extension services to reach more farmers.

(c) Five ways inadequate storage and processing facilities have affected agricultural development:

1. High post-harvest losses: much produce spoils and rots before it can be sold or used, wasting farmers' effort.
2. Reduced farmers' income: farmers are forced to sell perishable produce cheaply and quickly at harvest, lowering their earnings.
3. Seasonal gluts and scarcity: produce is abundant and cheap at harvest but scarce and expensive off-season, causing price instability.
4. Discouragement of large-scale production: farmers avoid producing more than they can store or sell, keeping output low.
5. Loss of quality and value: unprocessed and poorly stored produce loses quality, reducing its value and limiting export and industrial use.

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(a) Rosette disease of groundnut.

(i) Causal organism: a virus, the groundnut rosette virus.

(ii) Symptoms: stunted growth of the plant; yellowing (chlorosis) and mottling of the leaves; the leaves become small, curled and crowded together, giving a bushy, rosette-like appearance; there is general dwarfing and few or no pods are formed.

(iii) Method of transmission: it is transmitted from infected to healthy plants by an insect vector, the groundnut aphid (Aphis craccivora), which sucks the sap.

(iv) Damage done: it stunts the plants and reduces leaf area and photosynthesis, causing poor pod and seed formation; this leads to a heavy reduction in yield, and severe early infection can cause almost total crop loss.

(v) Preventive and control measures: plant resistant/tolerant varieties; plant early and at the recommended close spacing to reduce aphid spread; control the aphid vector with appropriate insecticides; rogue out and destroy infected plants; and practise good field hygiene and crop rotation.

(b) Plant population calculation.

Spacing per stand = 30 cm by 30 cm = 0.3 m by 0.3 m.

Area occupied by one stand = \(0.3 \times 0.3 = 0.09 \text{ m}^2\).

Total area of land = \(60 \times 30 = 1800 \text{ m}^2\).

Plant population = \(\dfrac{\text{total area}}{\text{area per stand}} = \dfrac{1800}{0.09} = 20{,}000\) plants.

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(a)(i) Surface drainage. It is the removal of excess water from the surface of the land by directing it into open channels, ditches, drains or furrows that carry the water away, usually by shaping and sloping the land so that water flows off freely. It prevents water-logging of the topsoil.

(ii) Three disadvantages of surface drainage:

1. The open channels and ditches occupy land that could otherwise be cropped.
2. The channels can cause soil erosion and gullying as the flowing water carries away topsoil.
3. They require regular cleaning and maintenance, since they easily become blocked by weeds and silt.

(b)(i) Irrigation. Irrigation is the artificial application of water to the soil (crops) through pipes, channels or sprinklers to supplement rainfall and provide the moisture needed for plant growth, especially during the dry season.

(ii) Two aims of irrigation:

1. To supply crops with adequate water for growth where rainfall is insufficient or unreliable.
2. To make dry-season (all-year-round) crop production possible and to increase yields.

(iii) Five problems associated with irrigation:

1. High cost of installing and maintaining irrigation equipment and structures.
2. Build-up of salts in the soil (salinity), which reduces soil fertility.
3. Water-logging of the soil when drainage is poor.
4. It can encourage water-borne diseases (such as bilharzia) and breeding of disease vectors.
5. Scarcity or unreliable supply of water at the source, and silting of dams and canals.

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The four major food nutrients required in livestock production, with two sources and two functions of each, are shown below.

(Vitamins and water are also essential dietary constituents; the four nutrients above are the standard answer required.)

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(a) Tractors. A tractor is a heavy, self-propelled engine-powered machine that provides the main source of mechanical draught power on the farm. It is used to pull and drive implements such as ploughs, harrows, ridgers, planters and trailers, and can supply power to other machines through its power take-off (PTO) shaft and hydraulic system. Tractors greatly reduce human drudgery and enable timely, large-scale land preparation and other operations. They may be wheeled or crawler (tracked) types.

(b) Incubators. An incubator is a machine that provides the correct conditions of warmth, humidity, ventilation and turning needed to hatch fertile eggs artificially in the absence of a broody hen. It maintains a temperature of about 37 to 39 degrees Celsius and suitable humidity, and turns the eggs regularly. It allows large numbers of eggs (for example chicks) to be hatched at the same time, which is essential in commercial poultry production.

(c) Sprayers. A sprayer is an equipment used to apply liquid chemicals such as insecticides, herbicides, fungicides and liquid fertilisers onto crops in the form of a fine mist or droplets. It breaks the liquid into small particles and distributes it evenly over the plants. Common types include the knapsack (back-pack) sprayer, the hand sprayer and the motorised or tractor-mounted sprayer.

(d) Shelters. Shelters are structures (housing) provided to protect farm animals from harsh weather (rain, sun, cold and wind), predators, theft and diseases. Good shelters keep animals comfortable and healthy, ease feeding, watering and management, and improve productivity. Examples include poultry houses, pig pens, cattle kraals and rabbit hutches.

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(a)(i) Marketing in agriculture. Marketing is the sum total of all the activities and business processes involved in moving agricultural produce from the producer (farmer) to the final consumer. It covers assembling, buying, selling, processing, grading, storage, transportation, financing and distribution, together with the exchange of ownership, so that the produce reaches the consumer at the right place, time and form.

(ii) Five stages involved in marketing agricultural produce:

1. Assembling (collecting the produce from scattered farmers).
2. Processing (converting the produce into usable/storable form).
3. Grading and standardisation (sorting produce into uniform quality grades).
4. Storage (holding the produce until it is needed).
5. Transportation and distribution (moving and selling the produce to consumers).

(b) Four agents of marketing:

• Wholesalers: middlemen who buy agricultural produce in large quantities from producers (or assemblers) and sell in smaller lots to retailers. They provide storage and bulk-breaking services.
• Retailers: middlemen who buy produce in fairly small quantities from wholesalers and sell directly to the final consumers in small units at convenient places such as markets and shops.
• Commission agents (brokers): agents who buy and sell produce on behalf of others and are paid a commission; they bring buyers and sellers together but do not usually own the goods.
• Cooperative marketing societies: associations formed by farmers to jointly assemble, grade, store and sell their members' produce, thereby securing better prices and reducing exploitation by middlemen.

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(a) Agricultural Extension. Agricultural extension is an informal, out-of-school educational service that takes useful, research-based agricultural knowledge, improved skills and new technologies to farmers and their families on their farms and in their homes. It teaches farmers to adopt improved practices so that they can increase their production, raise their income and improve their standard of living, and it also carries the farmers' problems back to research stations.

(b) Seven roles of an Agricultural Extension Worker:

1. Teaching farmers improved farming practices and new technologies (for example through demonstrations).
2. Passing on the results of agricultural research from research institutes to the farmers.
3. Conveying the farmers' problems and needs back to research stations and government for solutions.
4. Advising and guiding farmers on the selection and use of improved inputs such as seeds, fertilisers and agro-chemicals.
5. Helping farmers to form and run cooperative societies and other farmer organisations.
6. Assisting farmers to obtain credit, inputs and marketing facilities.
7. Motivating and encouraging farmers to adopt innovations, and helping to improve rural home and community life (nutrition, health and sanitation).

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(a) Two examples of crops in each group:

(b) Production of tomato.

(i) Sowing method: tomato seeds are first sown in a nursery (seed bed or seed box). Shallow rows (drills) are made and the seeds are drilled thinly, then lightly covered with fine soil and watered regularly. Sowing in the nursery gives strong, uniform seedlings before transplanting.

(ii) Transplanting: when the seedlings are about 4 to 6 weeks old and 10 to 15 cm tall with a few true leaves, they are watered, lifted carefully with soil around the roots, and transplanted to the prepared field in the cool of the evening at a spacing of about 60 cm by 45 cm. They are watered immediately after transplanting.

(iii) Varieties: examples of tomato varieties include Roma, Ronita, Ibadan Local, Beske and other improved and local varieties.

(iv) Harvesting: the fruits are ready for harvest about 3 to 4 months after transplanting. Mature fruits are picked by hand at the mature-green, pink or fully ripe (red) stage depending on the market; harvesting is done at intervals as the fruits ripen.