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Agronomy QUESTION #2090
Question 1
In organic farming systems, nitrogen fertility is maintained through which suite of mechanisms that must substitute for synthetic N fertilizers?
  • Urea application at reduced rates combined with biological control
  • Biological nitrogen fixation (legumes in rotation/intercropping), composted organic matter inputs, green manuring, crop residue recycling, and managed livestock integration — collectively building soil organic N pools and stimulating mineralization✔️
  • Exclusive use of rock phosphate and potassium sulfate
  • Deep tillage to expose and mineralize subsoil organic nitrogen reserves
Correct Answer Explanation
Certified organic systems prohibit synthetic N fertilizers. N supply relies on: (1) BNF through legume rotation (60–200 kg N/ha/yr), (2) compost and FYM application, (3) green manuring with leguminous cover crops, (4) crop residue decomposition, and (5) enhanced soil biological activity mineralizing organic N. The challenge is synchronizing N mineralization with crop demand — organic N release is weather and microbially dependent.