Irrigation command

[Baya]

Hey everybody,
I just have a short question. Is it possible to tell Daisy to only
irrigate for example for 5 minutes or is hours the shortest period I
can realize?
Thanks Matthias

[Per Abrahamsen]

On Thu, Sep 17, 2009 at 5:49 PM, Baya <beyer.m...@googlemail.com> wrote:

I just have a short question. Is it possible to tell Daisy to only
irrigate for example for 5 minutes or is hours the shortest period I
can realize?

Daisy uses hourly timesteps internally.  There is a top level timestep parameter you can set to change this, but most of the internal models have only been tested for hourly timesteps.  So I recommend leaving it alone.

  (timestep (minutes 2) (seconds 30))

The irrigate actions have a "remaining_time" parameter which can take a fraction of an hour.  E.g.

  (irrigate_overhead 10 [mm/h] (remaining_time 0.1 [h]))

Daisy will convert it to the internal timestep(s), so the above is really equivalent to

  (irrigate_overhead 1 [mm/h] (hours 1))

-- Per

[Baya]

Thanks for that quick answer.
I don't wanna mess with changing the internal time step so I better
leave it like this.

Anyway, I have another question. Do you have experience with modelling
greenhouse environments? We simulated our experiments in the
greenhouse with maize on sandy soil and the Daisy results show only
half of the measured plant height. If we double the global radiation
(only 50% of the outside global radiation was measured inside the
greenhouse), the results fit better. I'm still trying to figure what
the problem is so maybe you have an idea?

Thanks and Aloha,
Matthias

[Per Abrahamsen]

We haven't used Daisy for greenhouses, and several models will likely be wrong.  Most notable how we estimate potential evapotranspiration, but also photosynthesis will be different from field conditions.

Crop height in Daisy is a function of thermal time, but modified if stem dry matter is much below expectations.  If increasing global radiation helps, the low height is likely a symptom of either nitrogen or water stress.  Looking in crop_prod.dlf will tell you which.

By default, Daisy expect 200 g stem DM per m^2 for a crop to reach full height.  This is likely true for wheat, and haven't been calibrated for other crops.  Crop height does not affect other stuff in Daisy for normal usage, so it is not something we have looked much into.

-- Per

[Baya]

Alright, thanks your answer actually helps me a lot.
There are some papers dealing with the calculation of
Evapotranspiration in greenhouses/modification of Penman-Monteith
equation. I wanna try these and see if the model results improve...

The low simulated height must be a sign of water stress since nitrogen
stress has been turned off. The water stress is wanted since our
experiments are deficit irrigation experiments. We are not at the
point yet where we can compare other parameters but I'm really
interested what the results will be.

Thanks again, Matthias Beyer