Soil Fertility

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Organic farmers have different approaches to supplying crop needs compared to conventional farmers who provide fertility by numerous synthetic fertilizers. See the table below for differences between organic and conventional fertilizers.
However, even among organic producers, there can be different philosophies when it comes to supplying nutrients. Some believe it is important to keep fertility on-farm and avoid any external outputs. These producers gain nutrients for their crops from longer, diverse rotations with green manures and cover crops, and perhaps manure from their livestock. Other producers supplement organic practices with external amendments purchased from outside sources. Both viewpoints are valid and are based on a similar principle – to provide good nutrition for crops and develop healthy soils without environmental degradation.
Compost manure, animal manures, and green manures are examples of commonly used organic fertilizers for short and long-term fertility management. Other soil amendments can be mineral based such as rock powders and lime, or organically-based such as fish emulsions and kelp. Deficiencies must be documented with soil/tissue testing prior to amendments. Below are the amendments allowed under the National Organic Program.

  • Aquatic plant extracts (other than hydrolyzed)
  • Elemental sulfur
  • Humic acids (naturally occurring)
  • Magnesium sulfate
  • Soluble boron
  • Sulfates, carbonates, oxides, or silicates of zinc, copper, iron, manganese, molybdenum, selenium, and cobalt.
  • Liquid fish products
  • Lime (naturally occurring)
John Lamb
Craig Sheaffer
Kristine Moncada
University of Minnesota Extension