GK is just going to do optimisation sums (as that is what Curtin Uni probably wants me to do).
There are a lots of other interesting matters.
In an application like this real data matters - and it isn't necessarily easy to get.
Might the green-ness of the plant be measurable: lack of it indicate N-deficiency, photos, drones ...
Weather data can come from BoM (which also has monthly ET evapotranspiration data).
I tend to use google (and gemini) but there are wheat-growing specific sites.
ChatBCG
https://www.bcg.org.au/chatbcg/
I asked ChatGBC: Does BCG use APSIM for wheat crop simulations?
(Answer Yes - lots of detail)
BCG uses APSIM through the Yield Prophet tool to model daily nitrogen requirements and determine fertiliser input needs based on yield potential and seasonal conditions.
The model helps decide optimal timing for repeat nitrogen applications, with research showing that the majority of nitrogen can be applied after the end of tillering (GS30-32) without yield penalty.
Multiple nitrogen product forms have been tested (urea, UAN, calcium ammonium nitrate, ammonium sulphate), with trials consistently finding that timing of application is more important than product choice.
APSIM simulations guide split application strategies, allowing farmers to delay decisions until seasonal conditions become clearer and avoid over-investment in poor seasons.
The tool enables responsive nitrogen management by updating yield predictions monthly, helping determine if additional nitrogen topdressing will be profitable.
Many others have studied this. Earlier papers are given on othe pages, but for now, I mention:
Optimizing nitrogen topdressing for winter wheat by coupling remote sensing data with the DSSAT model
November 2025
Frontiers in Plant Science
Yu Zhao, Zeyang Wen, Chao Wang, Meichen Feng
DSSAT Decision Support System for Agrotechnology Transfer (DSSAT) is a (free) windows-based software application program that comprises dynamic crop growth simulation model
The technology around farming evolves.
Of particular relevance to the MISG26 N-fertilizer question is measurement of N in soil and indications of deficiency in crop.
See technology page for this (and at the bottom of that page links to miscellaneous topics).
The local Ag. Dept and many other organizations offer informal advice:
test your soil;
keep good records - experiment with a couple of different applications of N, e.g. in different plots, and use records to influence decisions in future years.
Various places suggest that as a function of amount and timing of N, the profit is fairly flat around the maximum.
The first part of the fertilizer problem asks for modelling of how nitrogen and water affects plant growth.
There are several aspects to this including
plantgrowth
climatedata
porousmediaflow
Other outfits have modelled crop growth.
People who are better than me at python (younger researchers) might be able to comment on
Python Crop Simulation Environment (PCSE)
https://pcse.readthedocs.io/en/stable/user_guide.html#background-of-pcse
For this and some of the many other simulation software see the plantgrowth page.
miscref Miscellaneous including organisations and references