Soil Fertility
What this domain tests
Domain 3 asks how you build and maintain fertility without soluble mineral fertilisers, on Cypriot soils that are typically calcareous (pH 7.5–8.5), low in organic matter (often under 1.5 %) and prone to erosion by intense winter rain. Expect questions on organic matter management, legume nitrogen, soil analysis and nutrient budgeting.
Core rules and concepts
- Fertility is fed, not injected. The aim is a living soil: organic matter, aggregation, biological activity, mycorrhizae.
- Legumes (vetch, clover, bitter vetch, faba bean, chickling vetch) fix atmospheric N; inoculation helps where the species is new to the field.
- Green manure and cover crops protect the soil surface from autumn storms, catch nitrate, smother weeds, then are incorporated or rolled.
- Rotation and root depth - alternate deep and shallow rooters, heavy and light feeders.
- pH and calcareous soils: avoid unnecessary liming; high pH locks up iron, zinc, manganese and phosphorus. Elemental sulphur can lower pH locally and slowly; organic matter and acidifying composts help more.
- Soil analysis every 3–4 years (pH, EC, organic matter, P, K, Ca, Mg, micronutrients); then a nutrient budget - crop removal versus inputs.
- Minimum disturbance: reduce deep ploughing, protect terraces, maintain stone walls and vegetative strips.
Worked example
A field is to be planted with processing tomatoes needing 150 kg N/ha. Hairy vetch is grown over winter and produces 3.5 t/ha dry matter at 3 % N. Reasoning: N in the biomass = 3,500 × 0.03 = 105 kg N/ha, of which roughly half (about 50–60 kg) is available to the following crop in the first season after incorporation, depending on incorporation date, moisture and C:N ratio. So the legume supplies around a third to a half of demand; the balance comes from compost (allowed animal manure within the 170 kg N/ha cap) and from mineralisation of soil organic matter. If vetch had reached 12 % C:N it decomposes fast; a stemmy, mature vetch with high C:N immobilises N and needs extra compost.
Traps that cost marks
- Quoting total N in a manure or residue as if it were all available in year one (typically 20–50 % for manure, more for young legume tissue).
- Ignoring the 170 kg N/ha/year manure nitrogen limit when "feeding the soil".
- Recommending lime on an already alkaline soil because "calcium is good".
- Forgetting that P is fixed by calcium in high-pH soils, so rock phosphate performs poorly there.