AFU Common Entrance Exam cheat sheet

Law of the Minimum (Liebig): yield is limited by the single most deficient nutrient, not by total nutrient supply.

Photosynthesis: 6CO2 + 6H2O + light → C6H12O6 + 6O2; C3 plants use RuBisCO directly, C4 plants first fix CO2 into a 4-carbon acid and are more water-efficient.

Soil pH ranges: strongly acid below 5.5, near-neutral 6.0-7.0 suits most cereals; legumes need pH above 6.0 for rhizobia nodulation.

Cation exchange capacity (CEC) rises with clay and organic matter content; sandy soils have low CEC and leach nitrate readily.

N-P-K labels give percent elemental N, P2O5 and K2O by weight; a 20-10-10 blend supplies twice as much N as P2O5 or K2O.

Crop rotation with a legume interrupts pest cycles and adds fixed nitrogen; continuous monoculture raises soil-borne disease pressure.

Seed germination requires adequate moisture, temperature above a species-specific minimum, and oxygen; light is a requirement only for some species.

Conservation tillage leaves at least 30% residue cover, reducing erosion but slowing early-season soil warming.

Ruminant digestion: rumen microbes ferment cellulose to volatile fatty acids; rumination and saliva buffer rumen pH near 6.0-6.8.

Rumen acidosis follows a sudden drop in fibre and rise in readily fermentable carbohydrate; rumen pH falls below about 5.5.

Body condition score is assessed by palpating ribs, spine and tail head; extremes at calving reduce fertility and raise metabolic disease risk.

Colostrum must be fed within the first hours of life because the neonatal gut absorbs antibodies only briefly before gut closure.

Normal rectal temperature: cattle about 38.0-39.0 C, sheep 38.5-40.0 C, pigs 38.5-39.5 C, dogs 38.0-39.0 C.

Notifiable diseases such as foot-and-mouth disease and anthrax require immediate reporting to veterinary authorities, not on-farm treatment alone.

Vaccination timing follows the primary course plus boosters; passive maternal antibody can block response in young stock.

Zoonoses (brucellosis, rabies, tuberculosis) transfer from animals to humans; control uses surveillance, culling and protective equipment.

Water quality targets for warm-water pond culture: dissolved oxygen above 5 mg/L, pH 6.5-8.5, unionised ammonia kept low.

Dissolved oxygen is lowest before dawn because respiration continues while photosynthesis stops; dawn sampling detects stress.

Pond fertilisation boosts natural plankton food; over-fertilisation causes algal blooms and night-time oxygen crashes.

Stocking density, survival rate and mean harvest weight together determine yield per unit area.

Fishing mortality (F) and natural mortality (M) combine into total mortality (Z); stock collapse risk rises when F exceeds the level giving maximum sustainable yield.

Induced breeding in carps uses pituitary extract or synthetic hormones; hypophysation triggers spawning outside the natural season.

Fish are poikilothermic: metabolic rate, feed intake and growth rise with water temperature up to a species-specific optimum.

Cage and pen culture depend on free water exchange; sites need adequate current and depth to avoid waste accumulation.

Silvicultural systems: clear-felling removes the whole stand, shelterwood removes it in stages under retained seed trees, selection fells scattered mature trees.

Diameter at breast height (DBH) is measured at 1.3 m above ground; it feeds volume and growth tables.

Mean annual increment (MAI) is total volume divided by stand age; rotation is often set near the age of maximum MAI.

Afforestation establishes forest on land without recent tree cover; reforestation restores forest on recently cleared land.

Agroforestry combines trees with crops or livestock; nitrogen-fixing species such as Leucaena improve soil for intercrops.

Forest fire risk rises with fuel load, low humidity and wind; controlled early burning reduces accumulated fuel.

Selective logging without adequate regeneration planning degrades stand quality; reduced-impact logging limits damage to residual trees.

Wood density and moisture content determine timber strength and drying behaviour; green timber shrinks as it dries.