Water and Nitrogen budgeting and DST

| June 19, 2015

Topic: Water and Nitrogen budgeting and DST

Water and Nitrogen budgeting and DST

This assignment is designed to give you experience in using decision support tools (Yield Prophet), and water and N budgeting. The assignment also consists of two parts, one to complete early, the other late in the semester.

Please attempt the first part of the assignment soon, as part of the value of having two parts is to see how the yield potential of your crop changes with the weather and time, so giving yourself several weeks between the first and second reports will give you more to discuss.


Aim: – The aim of this assignment is to expose you to decision support models, and to develop skill in the use of nitrogen budgeting and water use efficiency concepts for crop benchmarking and yield and fertiliser predictions. Water use efficiency is discussed in Topic 7, and nitrogen budgeting is discussed in Section 6.4.4, and both will be covered at the intensive school.
This assignment will require you to manage the nutrient and water requirements in a wheat paddock over the next 6 weeks.
Please show your calculations where required, and include the reports which you generate on Yield Prophet.
Yield Prophet
Yield Prophet® is an on-line crop production model designed to present grain growers and consultants with real-time information about their crops, providing integrated production risk advice and monitoring relevant to farm management. Yield Prophet operates as a web interface for the Agricultural Production Systems Simulator (APSIM), and generates crop simulations and reports to assist in decision making. By matching crop inputs with potential yield in a given season, Yield Prophet subscribers may avoid over- or under- investing in their crop.
The simulations provide a framework for growers and advisors to:
• Forecast yield
• Manage climate and soil water risk
• Make informed decisions about nitrogen and irrigation applications
• Match inputs with the yield potential of their crop
• Assess the effect of changed sowing dates or varieties
• Assess the possible effects of climate change
If you have questions about how to set up, run or interpret Yield Prophet, contact either Craig or Felicity first, then email yieldprophet@bcg.org.au

Assignment Tasks:-
Go to and login to Yield Prophet using the user name and password you have been given.
Select a region/paddock to monitor. You have a choice of Goondiwindi for NNSW/Qld, Lockhart for SNSW, BCG for Victoria, and Hart for SA.
Realistic information has been entered for each area which will be suitable for this assignment. However, if you want to change details to better reflect your local area or paddock, then you can modify the following:
• the paddock location and weather station used (select information to do this)
• the variety sown, sowing date, and population (select crop)
• soil N and water values , rooting depth, and stubble cover and type (select soil)
• application
If you use the Birchip paddock, the soil test results are on Moodle and you can enter them into Yield Prophet.
A couple of lines to a paragraph is all we are expecting as an answer to each point in a question, but remember to include the report you generated to get the information.
Report part 1: due on the 28th of August 2012.
1. What is your estimate of the yield of this crop? Base your comments on the climate forecast, and yield probability curves, and comment on the range of values.
Discuss the range of yields predicted with current nitrogen application, and when N is unlimited from now, and from the start of the season.
Will you apply Nitrogen now, assuming there will be enough rainfall ‘tomorrow’ to wash it into the soil.
2. Give your thoughts or comments on the following from the crop report
a. Crop rooting depth (now and the final limit),
b. water and N availability and stress,
c. likelihood of frost and heat stress affecting this crop.
3. Using the nitrogen comparison report, enter the following three scenarios to predict the most profitable timing for applying 50kg/ha of nitrogen:-
a. Growth stage GS14 (4 leaf stage early tillering)
b. Growth stage GS16 (6 leaf stage late tillering)
c. Growth stage GS31 (1st node stage)
Tip – use the crop report to determine the dates for application

Assume the following – grade APW, 10.5% protein, protein payment $5/%, grain price $300/t, nitrogen price $1.50/kg
Discuss the outcomes including which timing you would use, and why there are differences between timings.
Note: If your paddock has high levels of N applied at or before sowing and is not responsive to these applications, remove (or halve) this initial application and apply it at the above growth stages to see if you can improve on your existing strategy. Write a comment so that we can see what you have done.
4. Using the nitrogen comparison report enter the following three scenarios to predict the most profitable rate of nitrogen to apply at GS15
a. 25kg/ha
b. 50kg/ha
c. 75kg/ha
Discuss the predicted outcomes on the report, and what you would do with N application to your paddock.
5. Using the Irrigation comparison report and the most profitable rate of N from Q4, enter the following scenarios to add water to the crop (this could be rainfall or irrigation):-
a. Pre-sowing 75mm, 75% efficiency
b. GS16 75mm, 75% efficiency
c. GS65 75mm, 75% efficiency
Discuss the effect on yield, and the relative importance of rainfall/irrigation at the different growth stages.


This assignment has two aims – one is to give you some experience with decision support tools and crop models, while the second is to get you to think about yield outcomes from different agronomic set ups. Just as importantly, you should be thinking about yields during the growing season as a range of probabilities which will depend on the weather conditions leading up to harvest, rather than as a set yield in t/ha.

So when you create a crop report, you will see that the yield ranges from 2.5 to 5 t/ha (for example), with a median (50%) yield of 3.5, a 90% yield of 2.7 t/ha and a 10% yield of 4.5 t/ha (this is saying that 90% of the time, the yield will be more than 2.7 t/ha, and 10% more than 4.5 t/ha, and the highest on record is 5 t/ha).

Background information, including water, N, variety, planting date, population information – these have been setup based on actual paddocks in that area, so you can either go with these values, or change them to imitate a paddock you have an interest in – the choice is yours. If you have the information, changing would certainly give you mor relevant information and outcomes to think about.

You can also change the location of your paddock and weather station (and possibly the soil type), so that it more closely reflects your local area.

For Victorians, the BCG paddock isnt properly set up. You will have to enter the water, N, etc values from the sheet on Moodle. You will also have to change the soil type – the sandy clay loam (Corack No 740) is probably the relevant one for the area, but you could use any depending on how much clay you have in your soils. You will also have to put in a wheat variety, and time of sowing – I’ll track this down today and add it to this thread if you dont have the information yourself.

Hope this helps with the assignment – if you have any other quesitons or clarifications, post them here or email one of us.

I forgot to add comments on the reports…

The most useful reports to get the information you need for the assignment are the crop report, the crop and nitrogen comparison report (and maybe the profit reports), the irrigation comparison report and irrigation profit report. These will give you the yield (and profit) probability curves for your different cropping setups, as well as having other useful info on phenology timing, N and water deficits, frost and heat stress, etc, all of which are useful in describing why the crop is yielding what it does.

Some of you may have received an email titled Yield Prophet update. I am in the process of implementing Yield Prophet paddocks to monitor for your next assignment task. You could check out the links below so you understand what Yield Prophet is and how it is used.


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