Irrigation Effect

[Afiasarwar]

I am running apsim to check the effect of irrigation.I used 4 irrigation treatments of same quantity that is 75 ml on different dates and in second trial i changed the amount to 65 ml but it does not effect the yield?

[Keith-Pembleton]

Can you please post your simulation and the met file so we can take a look to see what is happening Cheers Keith

[Afiasarwar]

Thank you for your response.I have restriction from my supervisor on sharing simulation but i can give you full overview about this problem. we are basically running apsim for future scenerios usin RCM data from 2019 to 2099.we are interested in two types of adaptations that is sowing dates and irrigation adaptations.yield is effected by sowing date adaptation but not on irrigation.I have noticed that by keeping100% and 50% of inial water there is no effect on yield but keeping 0% of initial water c,early effect the yield so is it possible to keep intial water 0%?

[peter-devoil]

Of course. My back yard (in drought affected australia) was 0% up until a month or so ago.

The initial water is just that - a starting point. If you were able to measure the soil water content of your experiment at that time, then that's what you set it to. Anything else is an (educated) guess. After the first rainfall event it will be something else - water content is a state; and the simulation of that state has to start somewhere.

If you want to experiment further with how apsim responds to water supply; then drop the climate control (in the standard toolbox under the meteorological folder) into your simulation and reduce/increase the rainfall amount. It will be interesting to observe what happens if your environment has got extended dry spells.

[Afiasarwar]

Thank you Peter.But the problem is there is no drought in my study area.I have taken permission from my supervisor here is my simulation attached can you please figure out the problem?

irrigation.zip

[peter-devoil]

1. in tracker, change the "to" event to harvesting, not maturity. There is no event called maturity.
2. Add another: "sum of irrigation on end_of_day from sowing to harvesting as Cum_Irrig"
3. add Cum_irrig to report variables
4. set report frequecy = "harvesting'
5. I'd suggest not using P unless there is a demonstrated need. If you do, 5a. Add the phosporous component from standard toolbox/soil related/soil/Phosporous 5b. Configure with starting {labile/banded/rock}Phosporous 5c. in manager reseting; the name of your phophorous module is "Lyallpur Phosporous" 5d. Somehow find some wheat P parameters ... I can't run your wheat cultivar without the modified xml file, but can give pointers:
   • apsim's not going to do well with winter wheat. If that's your system we'll need help from experts.
   • your simulation doesnt grow large amounts of biomass, but I wouldnt expect it to under that temperature regime, even with large amounts of water & N.
   • check your phenology before you look at biomass/yield. If flowering / maturity time is off, you cant expect anything else to be "right for the right reasons".
   • check the water balance: starting water (50% of 263mm = 130mm), rain (20mm) & irrigation (4 * 55mm). What is transpiration saying?
   • as you say, changing rainfall amount won't affect much.
   • check the stress tables in the summary file. 0 means no stress.

We should continue this discussion over in apsim classic.

[Afiasarwar]

Thank you peter for your kind words 1.I have added Cum_irrig to report variables which is 165 mm. 2.i disabled phosporus module. 3.i am using spring wheat. 4.Initial water is 132 mm, cum rain is 23.2 mm, irrig is 4*55mm, Cum_transpiration is 108.99mm. 5.there is a little stress of water 0.013 , 0.042 in a stage of flowering to start grain fill units while 0.017, 0.022 stress from start grain fill to end grain fill units. But still i am unable to figure out the issue .here is my .xml file attached(pdf format) please have a look xml file.pdf

Thanks with anticipation

[peter-devoil]

Hi afia, can you please post the raw file (not a pdf) - you may need to rename it to .txt or add to a zipfile. The pdf format mucks up the xml..

As well, when do you expect your crop to flower and reach maturity?

Thanks

[Afiasarwar]

Here is Xml file attached. Wheat.zip flowering is expected in february and maturity in march.

[peter-devoil]

Hi afia, I've been able to run your simulation - your flowering and maturity dates are reasonable, so we can explore further.

As you see only very small water stresses in the summary, you can say there is plenty of water in this system, and as you've found, reducing it (by a total of 40mm, - 10mm at each irrigation) will have only a minor effect.

To guage the models response you'll have to remove more water - for example, by removing entire irrigation applications. Removing the 4th (scheduled for the day after harvest) encouragingly had no effect. The third reduced final transpiration by 4mm and biomass by 120kg. The second by 750kg. and so on. If you are adding water that the plant cannot use (at the top end of yields), the plant wont respond.

If you do enough of these "what ifs" you'll discover a moderately linear relationship between yield & transpiration - the French & Schultz relationship, popular in categorising rainfed systems down here. If you can confirm that experiment you should be happy.

But I expect that APSIM won't do a very great job in repeating your experiment a) if you haven't got measured starting water, and b) haven't got a timecourse of plant growth observations through the winter.