WAEC SSCE - Agricultural Science - 2011 (Essay)

Détails de la réponse

(a) Soil consistency

Soil consistency is the degree of resistance of the soil to deformation or rupture, that is the strength with which soil particles hold together (cohesion) and stick to other objects (adhesion) at different moisture contents. It is described as loose, friable, firm or hard when dry, and as sticky and plastic when wet.

(b) Influence of soil properties on crop growth

(i) Soil texture: texture refers to the relative proportion of sand, silt and clay. It determines how much water and air the soil holds and how easily roots penetrate. Sandy (coarse) soils drain fast and dry quickly, holding few nutrients, while clayey (fine) soils hold much water and nutrients but may become waterlogged and poorly aerated. A well balanced loam gives the best water, air and nutrient supply for crop growth.

(ii) Soil pH: pH measures the acidity or alkalinity of the soil. It controls the availability of plant nutrients; most crops grow best at slightly acidic to neutral pH (about 6 to 7). Very acidic or very alkaline soils lock up nutrients, may release toxic elements, and reduce the activity of beneficial soil micro-organisms, thereby limiting crop growth.

(c)(i) Four methods of maintaining soil fertility

1. Application of organic manure
2. Application of inorganic (chemical) fertilisers
3. Crop rotation
4. Cover cropping/green manuring (mixed farming and fallowing are also acceptable)

(c)(ii) How each method maintains soil fertility

• Organic manure: adds nutrients to the soil, and improves soil structure, aeration and water-holding capacity.
• Inorganic fertiliser: supplies specific nutrients (N, P, K) quickly, and corrects identified nutrient deficiencies to boost yield.
• Crop rotation: alternating deep- and shallow-rooted crops uses nutrients from different soil depths, and including legumes fixes nitrogen while breaking the pest and disease cycle.
• Cover cropping/green manuring: protects the soil from erosion and adds organic matter, and legume cover crops fix atmospheric nitrogen into the soil.

Détails de la réponse

(a)(i) Vegetative propagation

Vegetative propagation is the method of raising new plants from the vegetative parts of a parent plant such as the stem, root, leaf or bud (for example cuttings, suckers, tubers, bulbs, budding and grafting), without the use of seeds. The new plants are genetically identical to the parent.

(a)(ii) Advantages and disadvantages of vegetative propagation

Advantages:

1. The new plants keep exactly the good qualities of the parent plant.
2. Plants mature and bear fruit earlier than those raised from seed.
3. It is useful for propagating crops that produce few or no viable seeds.

Disadvantages:

1. It does not allow production of new/improved varieties (no genetic variation).
2. Diseases of the parent plant are easily passed on to the offspring.
3. The plants lack a tap root, are less vigorous and cannot be stored or transported over long distances as easily as seeds.

(b) Four cultural methods of controlling crop pests

1. Crop rotation.
2. Regular weeding and keeping the farm clean (field sanitation).
3. Early planting and early harvesting to escape pest attack.
4. Use of resistant varieties and proper spacing (destroying crop residues after harvest is also acceptable).

(c) Four harmful effects of chemical pest control

1. Chemicals may kill useful organisms such as bees, natural enemies and soil organisms.
2. They pollute the soil, water and air (environmental pollution).
3. Chemical residues on crops are poisonous and harmful to human and animal health.
4. Continuous use makes pests develop resistance to the chemicals.

Détails de la réponse

(a) Four ways in which rangeland is important in livestock production

1. Source of cheap natural feed: rangeland supplies natural pasture (grasses and legumes) which grazing animals feed on directly, greatly reducing the cost of buying feed.
2. Supply of water: streams, ponds and other natural water sources found within the rangeland provide drinking water for the livestock.
3. Space for exercise and free movement: the open land gives the animals room to move about and exercise, which keeps them healthy and reduces stress.
4. Shelter and shade: the scattered trees and shrubs on the rangeland provide shade and protection against harsh weather (sun, wind and rain).

(Also acceptable: habitat and breeding ground for natural mating; source of mineral licks and medicinal plants.)

(b) Carrying capacity of the rangeland

From the diagram, the rangeland is a stadium shape: a central rectangle with a semicircular end on each side.

• Length of the straight (rectangular) portion \(= 250\,\text{m}\)
• Width \(= 114\,\text{m}\), so each semicircle has diameter \(114\,\text{m}\) and radius \(r = \dfrac{114}{2} = 57\,\text{m}\)

Step 1: Area of the rectangular portion

\[A_{\text{rect}} = L \times W = 250 \times 114 = 28{,}500\,\text{m}^2\]

Step 2: Area of the two semicircular ends

The two equal semicircles together make one full circle of radius \(57\,\text{m}\). Taking \(\pi = \dfrac{22}{7}\):

\[A_{\text{circle}} = \pi r^2 = \frac{22}{7} \times 57^2 = \frac{22}{7} \times 3249 = 10{,}211.14\,\text{m}^2\]

Step 3: Total area of the rangeland

\[A_{\text{total}} = 28{,}500 + 10{,}211.14 = 38{,}711.14\,\text{m}^2\]

Step 4: Convert to hectares \((1\ \text{hectare} = 10{,}000\,\text{m}^2)\)

\[A_{\text{total}} = \frac{38{,}711.14}{10{,}000} = 3.87\,\text{hectares}\]

Step 5: Carrying capacity

Recommended grazing area per cattle \(= 3\,\text{m} \times 3\,\text{m} = 9\,\text{m}^2\).

\[\text{Carrying capacity} = \frac{\text{Total area}}{\text{Area per cattle}} = \frac{38{,}711.14}{9} = 4301.2\]

Since a fraction of an animal is not counted, the rangeland (about 3.87 hectares) can carry 4301 cattle.

(If the shape is read as a rectangle with only one semicircular end, the area \(= 28{,}500 + \tfrac{1}{2}(10{,}211.14) = 33{,}605.57\,\text{m}^2 = 3.36\ \text{ha}\), giving a carrying capacity of \(3733\) cattle.)

(c) Two benefits of each management practice

(i) Dipping

• Controls external parasites such as ticks, lice and mites on the skin and coat of the animal.
• Prevents parasite-borne diseases (for example anaplasmosis, babesiosis and heartwater) and keeps the hide healthy.

(ii) Vaccination

• Confers immunity, protecting the animal against specific infectious diseases such as anthrax, blackleg and rinderpest.
• Reduces the death rate and checks the outbreak and spread of epidemic diseases within the herd.

(iii) Artificial insemination

• Allows the use of semen from superior, proven sires so that the genetic quality and productivity of the offspring are improved.
• Prevents the transmission of breeding (venereal) diseases spread during natural mating, and lets one superior bull serve many cows even over long distances.

Détails de la réponse

(a) Deep litter system of poultry management

Advantages:

1. Many birds can be kept together in one house, so it saves space and labour.
2. The litter (droppings and bedding) can later be used as valuable manure.
3. Birds are protected from bad weather, predators and theft, and eggs are cleaner and easily collected.

Disadvantages:

1. Diseases and parasites spread quickly among the closely kept birds.
2. Damp or dirty litter produces ammonia, bad odour and can cause respiratory diseases.
3. It requires high capital for housing, litter and feeding, and birds may develop vices such as cannibalism and egg eating.

(b) Reasons for animal husbandry practices

(i) Castration of goats

1. To make the animals docile and easy to handle.
2. To improve the quality and remove the offensive smell/taste of the meat.
3. To prevent indiscriminate/uncontrolled mating and to promote fattening.

(ii) Creep feeding of pigs

1. To supply extra nutrients to the piglets since the sow's milk is not enough.
2. To help the piglets grow fast and reach weaning weight early.
3. To accustom the piglets to solid feed and reduce the stress of weaning.

(c) Four local breeds of cattle reared in West Africa

1. White Fulani (Bunaji)
2. Sokoto Gudali
3. Red Bororo (Rahaji)
4. N'Dama (Muturu and Keteku are also acceptable)

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(a) Ten differences between subsistence and commercial agriculture

(b) Sources of farm power

Détails de la réponse

(a)(i) Farm credit

Farm credit is the money or resources borrowed by a farmer from a source such as a bank or cooperative, to be used for farming operations and repaid later, usually with interest, over an agreed period.

(a)(ii) Five sources of farm credit

1. Commercial banks
2. Agricultural/development banks (for example the Bank of Agriculture)
3. Cooperative societies
4. Government loans and grants
5. Money lenders, friends and relatives (thrift/esusu societies are also acceptable)

(b)(i) Three main extension teaching methods

1. Individual (person-to-person) method
2. Group method
3. Mass (mass media) method

(b)(ii) Most appropriate method for creating awareness about the disease outbreak

The mass (mass media) method is the most appropriate.

(b)(iii) Two reasons for the choice

1. It reaches a very large number of farmers over a wide area within a very short time, which is important because the disease is spreading fast.
2. It is quick and cheap per farmer reached, so the warning gets to everyone before the disease spreads further.

(b)(iv) Three problems in using the mass method

1. There is no personal contact, so farmers cannot ask questions or get their doubts cleared (no feedback).
2. The message may be too general and may not suit the individual conditions of each farmer.
3. Many rural farmers may not own radio/television or read newspapers, and the message may be misunderstood or ignored.

Détails de la réponse

(a)(i) Agricultural extension

Agricultural extension is an informal, out-of-school educational service that teaches farmers improved and modern farming methods, carries the results of agricultural research to them, and helps them to solve their farm and home problems so as to raise their standard of living.

(a)(ii) Five demerits of cooperative societies

1. Poor and dishonest management can lead to loss or embezzlement of members' funds.
2. Many members are illiterate, which leads to poor record keeping and mismanagement.
3. Disagreement and lack of unity among members can break up the society.
4. Inadequate capital limits what the society can do for its members.
5. Delay in decision making because decisions are taken collectively (over-dependence on the society and undue government interference are also acceptable).

(b)(i) Three effects of rural-urban migration on agriculture

1. It causes shortage of farm labour because able-bodied young people leave the villages for the towns.
2. Farm output falls as farmland is left uncultivated or abandoned, leading to food shortage.
3. It leaves mostly the aged and weak to farm, so productivity and adoption of modern methods decline (cost of hired labour also rises).

(b)(ii) Three solutions to rural-urban migration

1. Provide social amenities such as good roads, water, electricity, schools and health centres in the rural areas.
2. Make farming attractive and profitable through mechanisation, credit, subsidies and good prices for produce.
3. Establish industries and create job opportunities in the rural areas to keep the youth on the land.

Détails de la réponse

(a)(i) Soil tillage

Soil tillage is the mechanical manipulation or working of the soil (by ploughing, harrowing, ridging, etc.) to loosen it, prepare a good seedbed, control weeds and create favourable conditions for planting and crop growth.

(a)(ii) Primary versus secondary tillage

Primary tillage is the first, deep and rough breaking of the land (for example ploughing) that opens up and loosens the soil, whereas secondary tillage is the lighter, shallow working done after primary tillage (for example harrowing and ridging) to break clods, level the soil and prepare a fine seedbed.

(b) Roles of soil management practices

(i) Green manuring

1. Adds organic matter and improves soil structure.
2. Increases soil nitrogen and fertility (especially when legumes are used).
3. Protects the soil surface from erosion and smothers weeds.

(ii) Mulching

1. Conserves soil moisture by reducing evaporation.
2. Controls weeds and moderates soil temperature.
3. Protects the soil from erosion and adds organic matter when it decays.

(c) Six reasons for irrigation in crop production

1. To supply water to crops during the dry season or periods of drought.
2. To make crop production possible all year round.
3. To supplement rainfall where it is inadequate or unreliable.
4. To dissolve and make soil nutrients and applied fertilisers available to crops.
5. To help in land preparation and softening of hard soil (as in paddy rice).
6. To reduce the harmful effects of high soil temperature and to leach out excess salts from the soil.

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(a) Contributions of science and technology

(i) Crop protection

1. Development of chemical pesticides, herbicides and fungicides for controlling pests, weeds and diseases.
2. Breeding of pest- and disease-resistant crop varieties.
3. Development of biological control methods and improved storage/spraying equipment to protect crops in the field and in store.

(ii) Climatology and meteorology

1. Accurate weather forecasting helps farmers to plan planting, spraying and harvesting.
2. Rainfall and temperature records guide the choice of crops and the timing of farm operations.
3. Early warning of drought, flood and storms allows farmers to take protective measures and reduce losses.

(b) Two functions of each farm machine/implement

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(a) Field pest versus storage pest

A field pest is a pest that attacks and damages crops while they are still growing on the farm (in the field), for example the grasshopper and stem borer, whereas a storage pest is a pest that attacks and damages harvested farm produce kept in storage, for example the weevil and rat.

(b) Two reasons for early harvesting of maize

1. To avoid damage and losses caused by field pests, birds and rodents.
2. To reduce spoilage from rain, mould and rotting and to prevent lodging of over-mature plants (early harvest of green maize also fetches a good market price).

(c) Methods of crop improvement

(i) Introduction: this is bringing in crop varieties or planting materials from another area or country where they have desirable qualities, and growing them in a new environment. If they perform well, they are multiplied and released to farmers.

(ii) Cross breeding (hybridisation): this is the deliberate mating (crossing) of two crop plants of different varieties, each having desirable qualities, so that the offspring combines the good qualities of both parents, for example high yield with disease resistance.

(d) Six factors to consider in selecting a crop variety

1. High yielding ability.
2. Resistance to pests and diseases.
3. Suitability to the local soil and climate.
4. Early maturing ability.
5. Market demand and consumer preference.
6. Tolerance to drought and adverse conditions (good storage/keeping quality is also acceptable).