I wish to shedule irrigation for a crop cultivar of which Kc value is unknown. Can't I use ETo directly without considering Kc since Kc is unknown?
Yes, you may try variable rates (25% higher and 25% lower of ET0), if possible also distribute these across distinct phenological stages (e.., initial, vegetative, reproductive, later/ fag stage) to establish your own strategy.
If no local crop coefficient (Kc) is available, the reference evaporation (ETo) can be used to determine the water requirement of the target crop.
Please see and enter this link to download my different papers (field, fruits Vegetables crops) using reference evaporation (ETo) to determine of water requirements and irrigation scheduling whit modern irrigation systems in Egypt
https./www.researchgate.net profile/Ahmed Taha 23
of course you can use ETo. Be sure to supply higher quantity than ETo per day or per week to avoid water unsufficiency and induce a stress. Moreover, you can perform regular measurement of soil water stock with deviner 2000 tool in case you have water regime as factor
Of course no, you will sur irrigate your culture. Take FAO Kc if you dont have information about Kc in your situation.
The key word there is 'schedule'. Irrigation scheduling is strictly based on ETcrop; so you cannot use ETo. I align myself with Amlal Fouad's suggestion for you. An improvised alternative is proposed below:
Set up a dummy trial of about three potted soils (serving as replicates) some two weeks or so ahead of your main trial. Grow the crop cultivar in the potted soils whereby you bring the soil to field capacity on daily basis, while also taking the weights of the potted soils on daily basis to determine the water use (ETcrop) between field capacity and a day after. You will be able to serially have the tentative values of the Kc by dividing the values of the ETcrop using the ETo which you already have. These Kc values you can use in your main trials trailing behind the dummy one. Hope this is clear and that it helps.
In condition the relationship between reference evapotranspiration (ETo) and the ETcrop (called kc coefficient) be calibrated for the study region
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