Composting and Organic Fertilisation
What this domain tests
Domain 4 covers making and using compost, manure and permitted fertilisers: getting the C:N ratio, moisture and aeration right, knowing when compost is mature, and applying manures legally so nutrients stay in the field rather than in the groundwater.
Core rules and concepts
- C:N ratio 25–30:1 at the start. Too high (straw alone) slows the process; too low (slurry only) loses nitrogen as ammonia.
- Moisture 50–60 % - the squeeze test: a handful should feel like a wrung-out sponge, no free water running out.
- Aeration by turning at windrow edges every 2–4 weeks; 3–5 turns over the cycle keeps the core aerobic.
- Thermophilic phase 55–65 °C for several consecutive days kills pathogens and most weed seeds; above 70 °C the heap dries and beneficial microbes suffer.
- Maturity: 2–4 months in Cyprus conditions, judged by a dark crumbly texture, earthy smell, low temperature, and a cress/lettuce germination test (immature compost is phytotoxic and robs nitrogen).
- Methods: windrow, static pile, in-vessel, vermicompost (cool, <30 °C, good for propagules).
- Permitted fertilisers under Reg. (EU) 2018/848 Annex II and Reg. 2021/1165: farmyard manure, compost, poultry litter, plant meals, seaweed extracts, wood ash, molasses, soft ground rock phosphate, potassium sulphate, micro-organisms. Synthetic NPK, urea, superphosphate and chelates are out.
- Storage: impermeable base, cover to keep rain out, away from wells and watercourses.
Worked example
A farmer mixes 1,000 kg of straw (0.6 % N, ~45 % C) with 500 kg of fresh grass clippings (2.4 % N). Reasoning: straw contributes 6 kg N and ~450 kg C; clippings contribute 12 kg N and ~200 kg C (dry-weight basis). Total = 18 kg N against 650 kg C → C:N ≈ 36:1, too woody, so the heap will heat slowly and lose little N but take months. To reach 25:1 the mix needs about 26 kg N, i.e. roughly 8 kg more N - add about 1 t of poultry litter or manure, or a similar nitrogen-rich material, then re-check the ratio before building the windrow.
Traps that cost marks
- Using fresh (uncomposted) manure close to harvest of leafy vegetables - a hygiene and certification risk.
- Judging maturity by compost age alone rather than by temperature, smell and a germination test.
- Spreading manure on wet soil, a slope, or before heavy rain; that is a Nitrates Directive and cross-compliance issue, not just a nutrient loss.
- Forgetting that the 170 kg N/ha/year cap applies to the total nitrogen of the manure applied.