The Future of Food Module 3.1.
Formative Assessment: mapping soil properties important for food production.
1. Please direct yourself to the online soil property mapper from the International Soil Resource
Information Centre (ISRIC) at http://soilgrids1km.isric.org/. Once at this website, you should see
most of the screen filled with a global physical map showing mountains, rivers etc. There are typical
navigation tools like in Google Earth for dragging with the mouse cursor clicked, zooming, panning
with arrow keys etc. The site may act slow at some times of the day.
2. There are commands across the top bar of the screen, including HELP which may be instructive if
any of the following is confusing.
3. You should see the word “download” at upper right, which means you are in the “view” mode
where you can visualize the values of soil properties on the map. If it says “view” mode click on that
so that you enter the view mode.
4. Notice the layers symbol (stacked squares) at upper right but below the toolbar. If you click on it, a
large sidebar will open and you can choose which soil variable you would like to visualize and/or
query. In this case visualize means to see the property mapped with a color scheme (theme) on the
map, and query means to right-click at a particular location and get the estimated data (e.g. percent
soil, classification of soil, pH of soil) for that location. You will be using the query function to identify
trends in soil parameters along gradients in climate.
5. Zoom the map to the continental U.S. Your map will look approximately like the first one below.
6. Click on the layers button at upper right and select the “pH in H2O” (pH of soil measured in a water
suspension) on the sidebar that appears. When the pH section of the sidebar expands just choose
the large default button which is pH in H20 between 0 and 5 cm soil depth You will see the map
start to fill in with a color coded representation of estimated soil pH on a 1 km grid (speed will
depend on internet traffic to ISRIC, likely). But ignore this to conduct your queries.
7. Now you will record 10 approximately evenly spaced pH values for soil along a transect (geographic
line along which data is taken) from the U.S. Southeast to the U.S. Southwest (an example line is
shown in red). You don’t need to actually draw this line on the map, just take the query data
approximately along the line using your eye. You should take ten values from east to west and
record them in the table below. Your transect line might look roughly like the one indicated on the
map image of the U.S. below. You’ll also do a second transect in South America (see below).
8. To take a point, use the query tool by left clicking on any point on the map, after setting the map to
show soil pH (step 6). You will see a popup box with the value for pH multiplied by 10, i.e. if it says
60 the pH is 6.0.
Transect
point
East to West, southern
U.S.: soil pHa
East to west, Amazon to the
Peruvian coast: soil pH
Soil Organic Matter values for one of
the transects.
1
2
3
4
5
6
7
8
9
10
a
Note that the ISRIC mapping utility uses a “x10” value for soil pH so you will have to divide by 10, in other words
if the query says 57 you should enter 5.7 in the table.
9. After completing the U.S. transect, zoom in on the Andes in Peru, South America (example transect
shown above in second image) and make a similar transect from east in the lowland amazon basin
to the Peruvian coast. After completing the two transects, answer the following questions:
a. What is the trend in east to west of soil pH in each of the transects?
b. What is the explanation for this trend? Think of at least two possible causes for this trend
and note them:
1. _____________________________________________
2. ______________________________________________
10. Now consult the global annual precipitation map at:
https://nelson.wisc.edu/sage/data-andmodels/atlas/maps/anntotprecip/atl_anntotprecip.jpg
11. What is the relationship between rainfall and soil pH you have verified?
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12. Based on the soil forming factors you understand now from the reading, at which end of the
transect would you expect mineral nutrients for plants such as Calcium, Magnesium, Phosphorus
and Boron to be most plentiful (in an undisturbed soil before soils are fertilized by farmers?).
13. What would you predict for the amount of organic matter in the soil along ONE of your transects,
and why?
____________________________________________________________________________
14. Now return to that approximate transect, change the variable shown in the ISRCIC layers to Organic
Carbon (the ORCDRC layer), and re-record the data for organic carbon in column 3 of the table
above. Is your prediction roughly true?
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15. Explore these layers (pH and organic C) and other layers in the data and see if you can notice any
other interesting pattern (e.g. about the amount of sand in soil; about soil properties in the place
where you are from, some global tropics to arctic pattern etc.) and describe that pattern briefly here
(a wide variety of responses will be acceptable, the point is for you to explore the data viewer in
some additional detail)
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