Module 3: The Nitrogen Cycle

Created 01/03/2023 - Last updated 23/05/2024

IMPORTANT NOTE: It is highly recommended that you upgrade your APSIM Next Gen version to at least version 2023.2.7164.0 or later.

The Nitrogen Cycle

In this exercise you will observe the cycle of fertiliser nitrogen in a fallow situation; urea to ammonium, ammonium to nitrate and the loss of soil nitrate via denitrification. This simulation will introduce editing a simple Manager rule and demonstrate more advanced features of graphing simulation results.

  1. Start a new simulation based on the Wheat example.
  2. Rename this simulation to Nitrogen Cycle.
  3. Save this file as Module3.
  4. The simulation will use a different weather file. To do this:
    • click the weather node
    • click the browse button
    • double-click AU_Dalby (C:\Program Files\APSIM[Version]\Examples\WeatherFiles) Change weather image
  5. In the Clock node, change the starting date to 1/1/1989 and the end date to 31/12/1989 Clock variables
  6. Add the Heavy Clay soil from the Training toolbox
  7. Delete Soil node
  8. Set Percent full to 50 in the Heavy Clay's Water node. change water % full
  9. Set starting nitrogen to 19kg/ha NO3 and 0 NH4, evenly distributed. Don’t forget to change units to kg/ha (right-click the column header ppm). Make the depth equal to the entire soil profile (check Water node for the profile depth). NO3 amount NH4 amount
  10. Delete all manager scripts (all have a farmer icon: SowingFertiliser, Harvest, SowingRule1)
  11. Copy a Fertilise on fixed dates management node to the field node. You can locate this by going to:
    • Home
    • Management toolbox
    • Fertilise folder
    • You can either drag this to your Field node or copy and paste it to the Field node. Fertilise on fixed date node
  12. Change Type of fertiliser to apply? to UreaN
  13. Change fertilisation date to 10-Jan
  14. Change Amount of fertiliser to be applied (kg/ha) to 100

  15. In the Report node let set up the output variables:

    [Clock].Today
[Weather].Rain
[Soil].SoilWater.Drainage
sum([Soil].SoilWater.ESW)
sum([Soil].NO3.kgha) as NO3Total
sum([Soil].NH4.kgha) as NH4Total
sum([Soil].Nutrient.DenitrifiedN) as Denitrification

  16. In the Report events section remove existing event variables. Then add:

    [Clock].EndOfDay

  17. Run the simulation

  18. Delete the current graph named Wheat Yield Time Series

  19. Add another Graph node to the Nitrogen Cycle simulation node

  20. Rename Graph to Nitrogen

  21. Add a Series to Nitrogen graph

  22. Rename Series to NO3 total

    • Variables for this Series NO3 total series variables

  23. Add another Series node to Nitrogen

  24. Rename this Series to NH4 total

    • Variables for this Series NH4 total series variables

  25. Create a new graph with a series each for rain, sum([Soil].SoilWater.ESW), NO3Total, Denitrification.

    • each series should have [Clock].Today as the X axis variable.

  26. From this chart you can see that significant nitrogen is lost via denitrification when large amounts of nitrate are available in saturated soil conditions. Denitrification graph

Congratulations on finishing the 3rd module!

Note: If you found any incorrect/outdated information in this tutorial, please let us know on GitHub by submitting an issue.