Posted: August 6th, 2015
GRNS 500 Grains Crop Production
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
Answering questions: For most of the questions, there is no completely right or wrong answer. What we want you to do is show us that you understand what is driving the system, or causing the differences/trends which you are seeing, and how these interactions between weather, soils, nutrients, and crop are important in managing a farming system.
When you are showing us that you understand, please keep your answers short – a couple of lines to a paragraph is all we are expecting for most points in a question. This saves time for you when answering, and for us when marking.
Include the relevant graphs from the reports – this will help your answer, and allows us to see the information you are basing your answers on.
Report part 1:
Generate a crop report for your paddock (Select Reports>Create>Crop Report Complete)
Q1. 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 predicted 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. Your comments should include the differences between wetter and drier years for the different N scenarios. Comment on whether yield has been lost up to this point from the lack of nitrogen.
Q2. Give your thoughts or comments on the following from the crop report
a) The amount of rainfall which has fallen so far, in comparison to historical records.
b) Crop rooting depth (now and the final limit),
c) water and N availability and stress,
d) likelihood of frost and heat stress affecting this crop. The important part of the table is the probability of frost or heat affecting the crop during flowering and grainfill. The other part of the table is whether the crop has experienced one of these stresses – this will not happen until flowering in Sept/Oct, and the information is useful in a postmortem of crop performance.
e) You are planning to spray fungicide to protect the flag leaf just after it has emerged – when are you likely to be spraying.
To get more information on heat and frost risk, you can use the sowing opportunity report on Yield Prophet to calculate when the window with the lowest risk of heat or frost stress is.
Q3. a) Using the Nitrogen Comparison Report (and possibly the N Profit Report), apply different rates of N to determine what you think is the optimum rate of N for this site (you don?t need to include these reports in your assignment). Then apply that rate of N at different timings to see whether timing is important in your region. I would suggest the following three timings to start with, but feel free to play with others if you want.
i. Presowing or at sowing
ii. Growth stage GS16 (6 leaf stage late tillering)
iii. Growth stage GS37 (flag leaf emergence)
Briefly discuss the results, including why there are differences between timings. You should also include comments on which of these timings (or other timing) you would use, and how other factors, such the initial N level, might influence your decisions.
b) Using the 60% Yield probability when nitrogen is non limiting (potential), calculate the crop nitrogen requirement using the nitrogen budgeting equations, then calculate the apparent crop nitrogen balance. Briefly discuss how this differs to the nitrogen requirement you calculated in
part a of this question and the value of this type of calculation as a prediction tool for nitrogen crop needs.
• Use the crop report to determine the dates these growth stages occur.
• Assume the following when using the N profit report – grade APW, 10.5% protein, protein payment $5/%, grain price $250/t, nitrogen price $1.50/kg
• If your paddock has high levels of N applied at or before sowing, and is not responsive to these applications, remove 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.
• Do not apply your N fertilizer before the date the N soil sample was taken, otherwise it won?t be recognized.
• For part b equations refer to your notes section 6 page 33.
Q4. This question is looking at the effect of starting soil water levels on yield. Go to the paddock Soil information to change the soil water percentage to the ranges suggested below:-
• If your location is Boggabilla decrease the starting soil water percentages to approximately 20% to 30% throughout the soil profile.
• If your location is Birchip increase the starting soil water percentages to approximately 20% to 30% throughout the soil profile.
• If your location is Hart or Lockhart increase the starting soil water percentages to approximately 25% to 35% throughout the soil profile.
• If your location is Merriden increase the starting soil water percentages to approximately 15% to 25% throughout the soil profile.
The actual water percentage isn?t important; it?s the difference between wet and dry profiles we are interested in. See the „Modifying the setup in YP? file on Moodle for how to change water if you don?t see what you should be doing.
Produce a crop report, and discuss the differences in yield between this scenario and the results from the initial soil water level (Q1). Include comments on the differences between the current and unlimited N yields, and between wetter and drier years.
***Change the soil water back to the original values when you have completed this question.
Q5. Using the Irrigation Comparison Report (Reports>Generate Reports>Irrigation Comparison Report) and the best rate and timing of N from Q3, enter the following three different scenarios to add water to the crop (this could be rainfall or irrigation):-
i. Scenario 1 Pre-sowing 100mm, 75% efficiency
ii. Scenario 2 GS16 100mm, 75% efficiency
iii. Scenario 3 GS65 100mm, 75% efficiency
Discuss the effect of increased rainfall/water on yield, and particularly the differences in response between the different growth stages.
• If your location is Boggabilla decrease the starting soil water to 20-30% before generating the irrigation report. Re-enter the original soil water before you go onto the next question.
• Use the crop report to determine the dates these growth stages occur.
Q6. Pick one of the other soils/regions which is completely different to your original (eg sandy v clay soil, summer dominant rainfall v winter – so NNSW v WA is ideal), and repeat Q4 for this site (ie, run a scenario using a wet starting profile, then repeat with a dry profile). Make sure that the crops have sufficient N. Comment on the differences between the two regions in terms of factors which would be important to understand if you were transferred to this area tomorrow as an advisor to growers. For example, the importance of stored water, likely yield potential across different seasons, possible stress on the crops, etc.
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