Soils, Soil Management and Plant Nutrition
Core concepts
Know the essential macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur) and micronutrients (iron, manganese, zinc, copper, boron, molybdenum, chlorine). Nitrogen promotes leafy growth, phosphorus supports roots and flowering, potassium supports fruiting, ripening and general vigour. Learn deficiency symptoms: yellowing older leaves often indicates nitrogen; purple tints can indicate phosphorus; marginal browning can indicate potassium.
Understand fertiliser types: organic (manures, composts, slow release, improves soil) versus inorganic (concentrated, fast acting, easy to over-apply). Know the meaning of a fertiliser analysis such as 10-10-10 (percent N, P2O5 and K2O) and how to calculate application rates. Understand soil management practices: crop rotation, green manures, mulching, liming to raise pH, and testing soil before applying nutrients.
Traps in questions
A frequent trap is over-application: more fertiliser is not better and can cause scorch or pollution. Another is confusing lime (raises pH) with sulfur (lowers pH). Candidates also forget that nutrient availability depends on pH, so a deficiency may be caused by wrong pH rather than absence of the nutrient.
Worked example
A 10-10-10 fertiliser means 10 percent nitrogen, 10 percent phosphate and 10 percent potash. To supply 30 g of nitrogen, divide 30 by 0.10, giving 300 g of fertiliser. Rule of thumb: test first, apply the calculated rate, and water in to avoid scorch.