Water balence for an orchard

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Water balence for an orchard

Post by mahardie » Fri Oct 18, 2013 12:00 am

I want to check if what i am doing is correct
I need to calculate a waterbalence for an orchard in hydrus 2D
I have weather station data, soil date etc.
In hydrus 2d i need potential E and potential T, I assume these to be the amount of water lost according to climate and leaf conditions with no restriction on avaiable soil moisture. Hydrus 2d then determines if the potential e and t are achieved based on daily avaiable soil moisture...is this correct.?
To determine the potential e and potental T can I use Hydrus 1d using penman-Montheith, tables > growth data with given LAI.
In the growth data table there is the column LAI/SCF is this LAI or SCF or LAI divided by SCF.
Im assuming it is LAI or SCF, thus I can set the LAI to 0 up to bud burst and maximum LAI at Harvest.
Does the growth file intergrate values between two time periods or apply then equilly at the specific times.?
Hydrus 1D then outputs the Potential evapotranspiration, potential transpiration, potential evaporation, are these values for potential E and potentential T oK to input into Hydrus 2D, or have they been influenced by soil moisture in Hydrus 1D and thus would result in error if I used them again in Hydrus 2d.?
Also if i wish to experiment with irrigation, would I need to re-run the hydrus 1D for new Pot E and Pot T with irrigation , or could I use the Hydrus 1d Pot T and Pot E without irrigation then use Hydrus 2D to experiment with the effects of irrigation on water budget in hydrus 2d without needing to re-run hydrus 1D.?

Thanks marcus
Ps I hope these questions make sence

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Re: Water balence for an orchard

Post by Jirka » Fri Oct 18, 2013 1:07 am

a. Yes, Hydrus reduces potential values of E and T based on actual (not daily) conditions (it is based on pressure head).
b. You can get potential E and T using different tools. Hydrus-1D, FAO tools, etc.
c. What is LAI/SCF? I guess I have just answered that in another topic. Basically, you choose yourself whether you want to specify LAI directly, or whether you want to evaluate it based on crop height data or from surface fraction covered by plant.
d. Integrate? I assume the question is "interpolate". If you use "Growth Data" table, then the values are interpolated in time. If you use "Meteorological Conditions" window, then values are constant for given time interval.
e. In Meteo.out (and graphs Meteorological information) gives indeed the potential values. Actual values are given elsewhere (T-level.out and Water Flow - Boundary Fluxes).
f. The potential values of E and T should not be affected by irrigation, rainfall, etc. It is purely based on meteo variables, such as incoming radiation.

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