Agricultural Ecology and Natural Resource Conservation
Ecology on the farm
An ecosystem is a community of organisms interacting with each other and with their physical environment. Learn the food chain (producer → primary consumer → secondary consumer → decomposer), the trophic levels, and the rule that only about 10% of energy passes to the next level - which is why top predators are few and why eating lower on the chain is more efficient.
Know the nutrient cycles: nitrogen (fixation, nitrification, assimilation, denitrification, leaching), carbon (photosynthesis, respiration, decomposition) and phosphorus (rock weathering, uptake, return in manure). Legumes fix nitrogen with Rhizobium bacteria in root nodules; that nitrogen enters the soil when roots and residues decompose, not directly from the air.
Understand conservation agriculture: minimum tillage, permanent soil cover (mulch) and crop rotation. Know erosion control, water harvesting, watershed management, agroforestry, rotational grazing, veld management and the meaning of carrying capacity. Learn the degradation processes - deforestation, overgrazing, desertification, bush encroachment, salinisation, pesticide pollution and biodiversity loss - and the management responses. Irrigation efficiency matters: drip uses less water than sprinkler, which uses less than flood.
Worked example - energy flow: 10,000 kg of grass supports about 1,000 kg of herbivores, which support about 100 kg of carnivores, which support about 10 kg of top predators. Apply the 10% rule whenever energy or biomass transfer is asked.