NSSCAS Agricultural Science 8222 cheat sheet

Namibia is classified as arid to semi-arid: mean annual rainfall ranges from under 50 mm on the coast to about 600 mm in the north-east, and potential evapotranspiration exceeds rainfall everywhere.

Rainfall is highly variable (coefficient of variation often 30-40 %), so stocking rates and crop choices must be based on long-term rainfall records, not on the previous season.

Main farming systems: communal subsistence livestock (cattle, goats, sheep) in the north and north-west, commercial cattle ranching on freehold land in the central and southern areas, and irrigated or dryland crop production in the north-central regions.

The Namib Desert and the Atlantic coast create the cold Benguela current, producing fog that supports livestock and wildlife in the pro-Namib; fog is not a reliable source of drinking water for production.

Crop production is concentrated in the north-central regions (Omusati, Oshana, Ohangwena, Oshikoto) where mahangu (pearl millet), sorghum, maize and groundnuts are grown, largely on sandy soils.

Carrying capacity is expressed in hectares per large stock unit (LSU); one LSU is roughly one 450 kg cow with calf, equivalent to about 6-7 goats or 5 sheep.

Bush encroachment by Acacia mellifera and Dichrostachys cinerea reduces grazing capacity; control options include selective thinning, debushing for charcoal or firewood, and controlled burning.

Namibia's Veterinary Cordon Fence separates the northern communal areas from the export zone to the south; movement of cloven-hoofed animals across it is controlled to maintain foot-and-mouth disease status.

Soil texture classes are defined by the proportions of sand (2.0-0.05 mm), silt (0.05-0.002 mm) and clay (<0.002 mm); a loam has roughly balanced fractions and is generally the most workable agricultural soil.

Most Namibian crop soils are deep aeolian sands with low clay and organic matter content, giving low cation exchange capacity (often below 5 cmol(+)/kg) and poor nutrient and water retention.

Soil pH affects nutrient availability: most crops grow best at pH 5.5-7.0 (water); aluminium toxicity becomes likely below pH 5.0, and phosphorus is locked up in both very acid and very alkaline soils.

Organic matter improves structure, water-holding capacity and cation exchange capacity; it is maintained by crop residue retention, manure application, cover crops and reduced tillage.

Wind erosion is the dominant erosion process on sandy Namibian soils; control measures include maintaining surface cover, windbreaks, strip cropping and avoiding cultivation during the dry windy season.

Water erosion control follows the rule: reduce raindrop impact (mulch, cover), slow runoff (contour ridges, waterways) and increase infiltration (organic matter, tied ridges, infiltration pits).

Essential macronutrients are N, P, K, Ca, Mg and S; micronutrients include Fe, Mn, Zn, Cu, B, Mo and Cl. Nitrogen is most often limiting in sandy soils because nitrate leaches readily.

Legumes fix atmospheric nitrogen through Rhizobium symbiosis; inoculation is needed where the appropriate rhizobia are absent, and the fixed N benefits the following cereal crop in rotation.

Germination requires viable seed, adequate moisture, suitable temperature and, for some species, light or scarification to break dormancy.

Pearl millet (mahangu) is the staple cereal of northern Namibia: it is drought tolerant, matures in about 90-120 days, and is established by broadcasting or planting in rows at the start of the rains.

Crop rotation with legumes (groundnut, cowpea, bambara nut) interrupts pest and disease cycles and adds nitrogen; continuous cereal monocropping depletes soil fertility.

Plant population is calculated as: plants per hectare = (10 000 / row spacing in m) / within-row spacing in m; correct density balances competition against yield per plant.

Weed control follows the critical period concept: crops are most sensitive to competition during early vegetative growth, so the first 4-6 weeks after emergence are decisive.

Irrigation scheduling based on evapotranspiration replaces water lost through the crop and soil surface; over-irrigation leaches nitrate and can raise the water table and cause salinisation.

Integrated pest management combines resistant varieties, crop rotation, sanitation, biological control and targeted pesticide use, with chemical control as the last resort.

Harvest and post-harvest losses are reduced by harvesting at physiological maturity, drying grain to about 12-13 % moisture, and storing in airtight or hermetic containers to prevent insect damage.

Ruminants digest fibre through microbial fermentation in the rumen; non-protein nitrogen such as urea can supply rumen microbes with nitrogen when roughage is low in protein, but urea is toxic if overfed.

A balanced ration supplies energy, protein, minerals, vitamins and water; the protein-to-energy ratio must match the animal's production stage (maintenance, growth, lactation, pregnancy).

Selective breeding uses heritability and selection differential: response to selection = heritability × selection differential; traits such as growth rate respond faster than lowly heritable traits such as fertility.

Crossbreeding exploits heterosis (hybrid vigour); the first cross shows maximum heterosis, which is lost in later generations unless a structured crossbreeding system is maintained.

Inbreeding increases homozygosity and exposes recessive defects; it causes inbreeding depression in fertility and growth, so unrelated sires should be rotated between herds.

Goats and sheep are browsers or mixed feeders suited to Namibian rangeland; cattle are grazers, so species mix should match the vegetation type.

Grazing management follows the principle of rest and recovery: rotational grazing allows palatable species to recover, while continuous grazing leads to selective overgrazing and bush encroachment.

Colostrum must be consumed within the first hours of life because it supplies antibodies and the gut absorbs them only briefly; calves and lambs without colostrum have high mortality.

Foot-and-mouth disease affects cloven-hoofed animals, causes vesicles on the mouth and feet, and is controlled in Namibia through movement restrictions, the cordon fence and vaccination in endemic zones.

Anthrax is a zoonosis caused by Bacillus anthracis; sudden death with dark tarry blood from body openings is typical, and carcasses must not be opened because spores form on exposure to air.

Rabies is a fatal viral zoonosis transmitted mainly by dog bites; post-exposure prophylaxis in humans and annual dog vaccination are the control measures.

Internal parasites include roundworms (Haemonchus, Ostertagia), tapeworms and liver fluke; control relies on strategic deworming, pasture rotation and avoiding overstocking around water points.

External parasites of livestock include ticks, mites, lice and blowfly; ticks transmit heartwater, anaplasmosis and babesiosis, so dipping or pour-on treatment follows a seasonal programme.

Notifiable or controlled diseases in Namibia include foot-and-mouth disease, anthrax, rabies, brucellosis, tuberculosis and African swine fever; suspected cases must be reported to the state veterinary service.

Vaccination principles: a vaccine must be stored at the correct cold-chain temperature, given at the correct dose and route, and the primary course completed before exposure.

Biosecurity measures include quarantine of new animals, disinfection of vehicles and equipment, control of visitors, and separation of sick animals from the herd.

Gross margin = gross income (yield × price) − variable costs; fixed costs are excluded because they do not change with the level of production in the short run.

Gross margin per hectare is used to compare enterprises competing for the same land; the enterprise with the highest gross margin per limiting resource is preferred.

Break-even yield = total fixed costs / (price per unit − variable cost per unit); break-even price = total costs / expected yield.

Partial budget analysis compares the extra costs and extra returns of a proposed change; the change is worthwhile if marginal revenue exceeds marginal cost.

Depreciation is the annual loss in value of an asset through wear, age and obsolescence; straight-line depreciation = (cost − salvage value) / useful life in years.

Farm records fall into physical records (yields, stock numbers, rainfall) and financial records (receipts, payments, inventory); both are needed for enterprise analysis and credit applications.

Marketing margin is the difference between the producer price and the consumer price; it covers transport, handling, processing and trader profit.

Price risk in livestock and grain marketing can be managed by forward contracts, spreading sales, storage when prices are seasonally low, and joining marketing schemes or cooperatives.

Tractor power take-off (PTO) implements are matched to tractor power; operating an implement that is too large for the tractor causes clutch and transmission damage and high fuel use.

Three-point linkage categories (I, II, III) are defined by pin size and spacing; an implement must match the tractor's category for safe coupling.

Diesel engines ignite fuel by compression heat; petrol engines use a spark plug. Diesel engines give higher torque at low speed and better fuel efficiency for field work.

Soil tillage implements: the mouldboard plough inverts soil, the disc plough cuts and partially inverts, the harrow breaks clods and levels, and the ripper loosens compacted layers without inverting.

Calibration of a sprayer: nozzle output (L/min) = flow rate per nozzle; application rate (L/ha) = (nozzle output × 600) / (boom spacing in m × forward speed in km/h).

Farm structures must match their purpose: a cool, dry, ventilated store protects grain; a well-drained concrete floor in a livestock shed prevents hoof problems and mastitis.

Fencing and water points determine grazing distribution; water points spaced too far apart cause uneven grazing, while correct spacing improves rangeland utilisation.

Safety rules for farm machinery: fit guards and shields, disconnect power before maintenance, never enter a running machine, and keep PTO shafts covered.

Sustainable agriculture balances three pillars: economic viability, environmental protection and social equity; a system that depletes soil or water is not sustainable even if profitable in the short term.

Conservation agriculture rests on three principles: minimum soil disturbance, permanent soil cover and crop diversification or rotation.

Climate-smart agriculture pursues three objectives simultaneously: increased productivity, improved resilience and reduced greenhouse gas emissions.

Adaptation options for Namibian farmers include drought-tolerant crop varieties and livestock breeds, early planting with the first rains, water harvesting, and diversified enterprises.

Mitigation differs from adaptation: mitigation reduces greenhouse gas emissions or increases carbon storage, while adaptation reduces vulnerability to climate impacts.

Bush encroachment, overgrazing and deforestation reduce carbon storage and increase erosion; restoration through reseeding, rotational grazing and tree planting reverses these trends.

Water harvesting techniques include tied ridges, infiltration pits, contour bunds, roof catchment and check dams; they capture runoff for later crop use.

Environmental impact assessment principles: identify impacts, assess their significance, propose mitigation, and monitor; farming activities near watercourses must respect buffer zones to protect riparian areas.

A hypothesis is a testable statement predicting a relationship between variables; the independent variable is manipulated, the dependent variable is measured, and controlled variables are kept constant.

A control treatment is essential in agricultural experiments because it provides a baseline against which the effect of the treatment is measured.

Randomisation and replication reduce bias and allow statistical estimation of experimental error; a single unreplicated plot cannot support a reliable conclusion.

Soil texture can be estimated in the field by the ribbon test: moistened soil is squeezed between thumb and forefinger, and the length of ribbon before breaking indicates clay content.

Soil pH and nutrient status are determined by laboratory analysis of a composite sample taken with an auger in a zigzag pattern across the field at 0-20 cm depth.

Seed viability can be tested by a germination test: count germinated seeds as a percentage of seeds sown after a set period under moist, warm conditions.

Plant disease diagnosis uses symptom recognition, examination of affected tissue and, where needed, laboratory culture or molecular testing; correct diagnosis precedes any chemical treatment.

Data presentation: tables for exact values, bar charts for comparing categories, line graphs for trends over time, and scatter plots for relationships between two measured variables.