Hi everyone. I am trying to simulate the crop yield from vegetative stage, flowering stage, and maturity stage. I have results for moderately and extremely sensitive to water stress but I am having a difficulty in obtaining results for NO WATER STRESS..how do I get results for no water stress?
Thanks.
You need results of full and deficit irrigation treatments from field experiments to calibrate and validate Aquacrop model for your production conditions.
Dear Catherine
A simple practical answer is, if plants are grown in soil, to water regularly allowing the soil to drain between watering. The soil should be free draining so that good aeration is maintained. If the evaporation rates are not very large, then this gives the unstressed state. The measurements over the period give the plant responses: they should be relatively stable .
Hello,
You can set the irrigation parameter to field capacity; so that the model applies an irrigation before reaching a water stress.
Best,
Chafik
Chafik Abdallah thanks...
But to do that, I need a practical approach although I know that the TDR is the best method to do it and I do not have access to it.
Hello Keyvan,
TDR is a method of measuring water content; it is not required - you can achieve a moist soil by watering well at regular intervals and allowing drainage (to keep good aeration)between them. You could measure soil water content by taking samples - if you do that with watered, drained soil without plants it will show what a controlled soil water content should be. Then sampling of the soil with plants growing in it will show how the water content compares. Also, measuring the relative water content (RWC) of the plant's leaves will show how well the plant is watered: good watering gives values of RWC above 95% or so. The methods are described in the literature. If you try looking up soil water content measurement and RWC measurement you will find information.
Regards
David
In my opinion you should set your irrigation application according to a soil moisture condition. This could be done as said before by setting your irrigation strategy as 'IrrigationRate=θFC-θ' indeed, i.e. applying the necessary amount to restore soil back to field capacity, everytime θ0.31 θFC)... of course you can also get below the last threshold during the phenological senescence stage, but this would be already considered some kind of controlled deficit irrigation strategy (Fereres, E., & Soriano, M. A. (2006). Deficit irrigation for reducing agricultural water use. Journal of experimental botany, 58(2), 147-159). Note that these thresholds, instead of field capacity, allow you to better avoid water excess (and consequent biomass loss) and do not compromise your water requirements at all.
So the best practice would be the combination of the first two thresholds, or if water is not a limiting fator, just irrigate to keep θ above about 80% of your θFC... please note this values are calibrated for maize... you can explore the proposed thresholds of other pre-calibrated crops by clicking on crop specifications in the model (user software), and looking at the water stress parameters. If you wish to explore AquaCrop with other crops you will have to calibrate it yourself by measuring those thresholds in the field (for that you can use indeed TDR if well validated, or neutron probe).
I hope this might help... have a look at this example with AquaCrop for maize.
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