Why agricultural ecosystems lose nutrients
In a natural ecosystem, nutrients contained in dead organisms and waste are returned to the soil through decomposition by saprobionts. This allows mineral nutrients to be reused by producers.
Agricultural systems differ because biomass is deliberately removed:
- crops are harvested
- livestock are removed from the ecosystem
The mineral nutrients incorporated into that biomass are therefore not all returned to the soil. Repeated removal can disrupt nutrient cycling and reduce soil fertility.
Replacing the loss
Fertilisers are added to agricultural soils to replace mineral ions lost in this way, particularly nitrate and phosphate ions.
Nitrogen fertilisers can increase crop yield, helping agricultural systems produce more food.
harvesting and livestock removal → nutrient loss → fertiliser replaces mineral ions
Exam Tip: Explain the need for fertiliser as a nutrient-cycle problem: biomass is removed at harvest, so its mineral nutrients are not returned to the soil and must be replaced.