How is mineralization handled in the Granular Crop Model?

Residue information includes percent nitrogen and percent carbon (including a breakdown of carbohydrates, cellulose, and lignin) and decay rates of each. There are currently two options for residue: soybean and corn/other. We expect to add options for other residue types and cover crops as we are able to complete research to define appropriate values.

• Soybean residue contains a higher percent of nitrogen (that is, lower C/N ratio) and breaks down to release nitrogen more quickly.
  • Soybean residue is treated as three different pools of organic matter (above-ground biomass, roots, nodules) to account for the differing C/N ratios and breakdown rate.
  • Expect 30-50 lbs N/ac to be released from soybean residue through mineralization by VT/R1 under typical growing conditions and only a few pounds the rest of the season. Soybean residue starts to mineralize on the November 1st.
• Corn/other residue mineralizes more slowly with a significant portion not becoming available until after VT/R1.
  • Corn residue is separated into two pools: above-ground biomass and roots.
  • Expect 25-60 lbs N/ac to be released by VT/R1. Corn residue starts to mineralize on the November 1st.
• Soil organic matter mineralization is modeled based on soil organic carbon (estimated from organic matter content), water-holding capacity, soil temperature, and more. At present, there is no distinction between different types of organic matter for high organic matter soils such as peats and mucks, but is a possibility for future development.
• Manure is set up as a nutrient product with appropriate places to enter nutrient composition or accept the book-value defaults provided in the system based on the selection of species and manure-management practices.
  • Select the appropriate manure type. The system automatically populates book values in the appropriate spots.
  • Users can modify the values based on manure test results or based on local university book values.
  • Manure is separated into two applications.
    • A fertilizer application accounts for the immediately available inorganic nitrogen fraction and is entered in the Ammonium (NH4) field in the user interface.
    • A residue application approximates the slower mineralization of organic matter. Enter the percent organic nitrogen to define the amount of organic carbon in the manure source and the percent available in the first year to define how much of that organic carbon will be mineralized in the first year.
• The product currently does not account for manure nitrogen contributions in the second and subsequent years.
  • To account for manure in the second or third growing season after application, add a manure application as usual, but replace the default values for the second year with book values provided by many universities.
    
  • If university values are not available for subsequent years, zero out the inorganic nitrogen contribution and reduce the amount of organic nitrogen defined for the first year by approximately 50% for second year applications and by approximately 75% in the third year.