SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Step 1. access SGRASIM site from
Dr. Tong Zhai
http://cobweb.ecn.purdue.edu/~grasim/sgrasim_inst.html
Step 2. The initial input page as shown below:
You can select multiple forage species, such as shown above (hold down
Ctrl key to select species that are not next to each other).
Then specify growing season starting date and ending date as shown above.
Then click ‘Save’ button.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Step 3. Specify Tree inputs by clicking on the ‘Modify Tree variables’
button:
Type in inputs as shown above, then click the ‘Save’ button. The model can
simulate both deciduous and evergreen tree types, however, I haven’t
tested the interface for evergreen yet.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Step 4. Click on the ‘Modify Crop variables’ button to modify/save forage
growth parameters:
For your test run, just change the ‘specific leaf area’ parameter for
Alfalfa to 39, then scroll down to the bottom of the page and click the
‘Save’ button.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Step 5. Click on the ‘Modify soil variables’ button to modify/save soil
parameters:
For this test run, change the ‘Top soil layer wilting point’ to 0.15 and
‘Bottom soil layer wilting point’ to 0.18 (these are water content by
volume) to allow more available water in the soil profile. Then click
‘Save’ button.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Step 6. Click on the ‘Modify Nutrient variables’ button to modify/save
nutrient parameters:
First, we are going to modify the number of fertilizer applications to
correspond with the growing season length we specified earlier in the
first input page. It is a two-step process. First step, change the ‘Number
of N Fertilizer Applications:’ input for paddock 1 (P1, or field 1, this
is to signify that future version will be able have multiple paddocks or
fields as you already see for the GRASIM model interface) to 2 (meaning we
only going to apply fertilizer twice during the growing season), then
click on the ‘Save’ button to make this change take effect as shown below:
Then, second step is to specify the day of year and type and amount of
fertilization in the two input fields immediately below the ‘Number of N
Fertilizer Applications’ input field. As the legend specified, the two
lines of input each consists of 4 components (or 4 numbers). The first
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
number is the day of the year that you want to fertilize, the subsequent
three numbers are the amounts of fertilizer (kg/ha) for each of the three
kinds of fertilizers considered, i.e., nitrate based (NO3-), ammonia based
(NH4+), and organic (manure) fertilizer. So change the two lines of
numbers as follows:
This essentially is saying that you fertilized with 60 kg/ha NO3
fertilizer (active ingredient) on the 167th and 249th day of year 2000 (June
15, and Sep 5, 2000, respectively). (I know, I will put this little
calculation up in the interface). Then click ‘Save’ again to finalize this
input page.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Step 7. Click on the ‘Modify Initialization variables’ button to
modify/save initial conditions for the simulation:
In this input page, only change the ‘Initial structure biomass’ for the
three species of forage to 0.008, 0.007, and 0.006 kg/m2 for orchardgrass,
tall fescue, and alfalfa respectively, as shown above.
Then, scroll down and click ‘Save’ to finish this input page.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Step 8. Click on the ‘Modify Management variables’ button to modify/save
grazing management for the simulation:
The actual model can handle all the four types of grazing schemes as shown
in the interface above, however, I haven’t tested the interface yet for
this capability, so for this test run, once this input page is loaded,
just click on ‘Save’ to finish it.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Lastly, click on the ‘RUN GRASIM’ model button to run the model,
momentarily, you will be presented with this output page:
There are five categories of outputs:
Biomass: above ground standing biomass time series for the three forage
species we chose in the first input page
Soil moisture: the soil moisture content (mm) dyanmic for the top 30 cm
soil profile and the bottom 70 cm soil profile
Drainage: percolation from the top soil layer to the bottom soil layer and
that from the bottom soil layer to below the root zone
Soil Nitrage: the soil nitrate content (kg/ha) dyanmic for the top and
bottom soil layers
Leaching: the soil nitrate leached from the top to bottom soil layer and
that from bottom to below root zone soil layers.
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SGRASIM (Silvopasture GRAzing Simulation Model) tutorial, September 19, 2007.
Dr. Tong Zhai
Weather: shows the daily weather data used for this simulation which
include: Day_of_year, Date,Tavg,Tmin,Tmax (C), rainfall(mm),
solar_radiation (w-min/m2), windspeed_at_topoftreecanopy(m/s), RHavg,
RHmin, RHmax(percent)
Tavg,Tmin,Tmax, are the daily average, minimum, maximum temperature in C
RHavg,RHmin,RHmax, are the daily average, min,max relative humidity in %
All of these output and input are presented both in tables and graphics.
You can explore on your own, the only thing I want point out is that the
drainage and leaching outputs, they are all zeros for this particular test
run, meaning there is no loss of soil water and nutrient due to downward
flow from the soil root zone (or the top 1 meter soil profile considered
by the model).
Also, when you navigate through the above input interface pages, use the
input category buttons, don’t use the ‘Back’ or ‘Forward’ buttons in your
browser.
Once you reach the output page, you can use the ‘Back’ ‘Forward buttons in
your browser.
I hope this tutorial can help you get a initial feel of the model. I agree
that the interface is not anywhere near user-friendly, just an initial
development stage, will continue to make it better, this would be
especially true, if we can collaborate on this effort further. Please let
me know.
Best regards,
Tong.
Tong Zhai, Ph.D.
Department of Ag & Bio Engineering
Purdue University,
West Lafayette, IN 47907
E-mail: [email protected]
URL: http://pasture.ecn.purdue.edu/~tzhai/
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