Monitoring nutrient mineralization

As mentioned above, you can use standard soil and nutrient mineralization tests to monitor soil nutrient availability. However, organic nutrient management relies not only on nutrients available at the time of soil sampling but also on the nutrients released through mineralization during the growing season. Unfortunately, there is no easy or inexpensive test that assesses when, which, or how many nutrients are released from crop residues or mineralizing organic matter. Instead, you will need to estimate mineralization rates based on the following criteria.

  • For compost, manure, poultry litter, or mulches
  • Nutrient analyses of material
  • Application rate (pounds per square foot or tons per acre)
  • Date of application
  • Cover crops and green manures
  • Crop grown as a cover crop or green manure
  • Whether a legume cover crop was inoculated with nitrogen-fixing bacteria (Rhizobia species)
  • Growth stage at which it was cut or incorporated (Cut the cover crop when it is at 50% bloom, unless your farm is in an arid area where this level of cover crop growth would deplete water needed for your primary crop. This is the prevailing recommendation for maximum nutrient availability for the next annual crop.)
  • Yield level
  • Nutrient value of the residues left in the field
  • Management of the cover crop after its growth was terminated (Was it left on the soil surface as a mulch or was it incorporated into the soil?)
  • Environmental conditions following application of plant or animal materials (Mineralization occurs most rapidly under warm, moist conditions. It will slow down considerably during winter or during drought.)
  • Mineralization over time (Only a portion of the nutrients from organic matter becomes available during the first year following application. Accurate nutrient management accounts for nutrient mineralization over several years, not just during the current planting season.)

See References for publications and Web sites that provide detailed information on how to estimate nutrient availability based on these criteria.

For information on potential nutrient availability from various organic inputs, see the ATTRA publication Protecting Water Quality on Organic Farms.

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