Environmental Science and Sustainable Agriculture: Pollution and Resource Conservation
This domain tests pollution from farming, greenhouse gases, soil degradation and the practices that keep a farming system productive over decades.
Pollutants and greenhouse gases
Carbon dioxide, methane and nitrous oxide are the agricultural greenhouse gases. Methane comes from flooded paddy and ruminant enteric fermentation; nitrous oxide comes from excess nitrogen fertilizer and manure. Ozone depletion is caused by chlorofluorocarbons, not by farm emissions. Burning residue and excessive tillage degrade soil organic carbon.
Sustainable practices
Crop rotation with legumes, green manuring (sunhemp, dhaincha), farmyard manure and vermicompost, mulching, conservation tillage and zero tillage, integrated pest management, agroforestry, watershed development and biogas plants from dung. Organic farming permits approved biological and botanical inputs and does not mean zero management; yields usually need a long conversion period.
Worked example
A farmer applies 10 tonnes of farmyard manure per hectare. At 0.5% nitrogen, that supplies 10,000 × 0.005 = 50 kg N. But only about 30% of manure nitrogen becomes available in the first season, so the effective supply is 50 × 0.30 = 15 kg N - roughly one-third of the nitrogen in 100 kg of urea, which carries 46 kg N. That is why organic sources must be credited on available, not total, nutrients.
Traps
- Naming CFCs as an agricultural greenhouse gas.
- Assuming organic farming forbids all plant protection, when approved biologicals are allowed.
- Crediting manure at its total nutrient content rather than available content.
- Forgetting that flooded rice is a major methane source.