Crop Coefficients


#1

So I’ve been trying to update all the parameters in my zones so I can use the full potential of the controller. Was wondering if anyone had been playing with crop coefficients. It looks like it’s something that changes throughout the season, around 3 times a year. Is that correct? Are people keeping it updated throughout the year?


#2

@JPedrego I’m still optimizing like you are. My plan was to set and forget the crop coefficient for the most part, starting fairly close to the defaults. This Rachio support article does suggest that changing it throughout a season might be in order if your vegetation it’s going through stages of development. I’m not sure if there are other reasons to do so.


Zone Settings for Subsurface Drip Tubing
#3

I’d find a good value and just leave it. An average should work just fine.

Note that current flex schedules DO NOT use the crop coefficient on Advanced zone settings. Still trying to catch up, hoping to start using that value sometime next week in flex schedules. I really don’t want to use it in existing flex schedules since it might have a big impact on users that have their schedules dialed in, but will have it on any new flex schedules. It is probably the single easiest value to modify to change watering frequency throughout the year.

For current flex schedules we do use a a range of values each month per turf type. Here is the list of values, which I like I said will be replaced for flex with just using the crop coefficient in the zone Advanced settings.

Cool season grass:
JANUARY, .61
FEBRUARY, .69
MARCH, .77
APRIL, .84
MAY, .90
JULY, .93
JUNE, .93
AUGUST, .89
SEPTEMBER, .83
OCTOBER, .75
NOVEMBER, .67
DECEMBER, .59

Warm season grass:
JANUARY, .52
FEBRUARY, .64
MARCH, .70
APRIL, .73
MAY, .73
JUNE, .71
JULY, .69
AUGUST, .67
SEPTEMBER, .64
OCTOBER, .60
NOVEMBER, .57
DECEMBER, .53

Here is a good range of values:

Here are some examples of values the EPA uses for their testing:

http://www.epa.gov/WaterSense/docs/final_controller_specification_102611_final508.pdf

:cheers:


Flex schedule *change*, using crop coefficient from zone
Negative Moisture levels?
Flex schedule *change*, using crop coefficient from zone
#4

Ok, so I was hoping to use the crop coefficient after converting all of my schedules to flex so if it’s not be currently being used then I will hold off for now.

Is the coefficient only useful for turf? I was going to try to change it for my trees just so I can get a good schedule going.


#5

@JPedrego If you want to wait until next week going to promote all the code then (for flex).

Here are the default values for other crop types (we don’t use a steeped model for them, just one value).

0.3 Xeriscape
0.75 Trees
0.55 Perennial
0.8 Annual
0.5 Shrubs

:cheers:


#6

@franz Interesting, and good to know. So in your updated flex algorithms, what will drive the seasonal change in frequency if not cc?


#7

The weather :wink:

:cheers:


#8

Ok, so I wasn’t too concerned about the crop coefficients for my turf, it was more my trees I was worried about. Specifically that only one value is used for trees. I imagine there would be some pretty big differences between a citrus tree and other fruit trees. Sounds like I would need to find those numbers and vary it throughout the season to get the best watering schedule for a specific tree.


#9

@Franz. Fair enough. Maybe I should rephrase. If I were to recreate a new Flex schedule after you release the update, and input all of the same values verbatim from my old Flex setup, should I expect any differences in my watering ?


#10

The only difference is that we would be using the crop coefficient on the Zone, rather than the adjusted table above. I can’t say if it would be watering better/worse for you. The value we chose was an average, so assuming over the year would even out.

:cheers:


#11

@franz Got it. It seems like there would indeed be a difference in the watering, but not necessarily a bad one. Thanks for the explanation.


#12

Crop coefficientso do not change. Just select the correct plant material for each zone with the associated crop coefficient. Runtime or irrigation frequency will change or even cease. You can read up on ET if you go to the Arizona Cooperative Extension website to read about crop coefficients.


#13

Resurrecting this thread since I tried looking at crop coefficients again. I was trying to set the coefficients for me veggie garden. I found a coefficient of 1.15 for tomatoes and figured that I would use that. But the field in the app shows a percentage with a Max of 100%. Did I find the wrong parameter? I would expect to be able to set a value of 115% if they are the same


#14

JPedrego were you able to figure this out? We have a bunch of containers that are all full of veggies and wanted to know what to use.

thanks!


#15

@JPedrego We only support a crop coefficient up to 100%. If you went over 100% it would be more than the daily ET, which I don’t know how that is possible?

:cheers:


#16

Just to make sure I’m looking at the correct parameter, in the below equation:
ETc = Kc ETo
Crop coefficient = Kc?


#17

Yes. If you had ET of .2in for the day, and a crop coefficient of 115%, then your ET for the day would be .23in.

I don’t know if that is physically possible (but doesn’t seem like it), is that your desired effect?

:cheers:


#18

I don’t know if I’d say it’s my desired effect. I was just doing some searches for what the proper crop coefficient for tomatoes was so I could switch the veggie garden over to flex. Multiple sites showed a crop coefficient between 1.05 and 1.25 for the plant at its current stage of growth.


#19

@JPedrego Ok interesting, hadn’t thought about that scenario. I’ll add it to our software backlog.

:cheers:


#20

As an aside, when I was researching similar topics myself, I found that tomatoes root depth is 24 inches!!! Please post what you end up setting things up and how well it works.