![](media/image1.pct)Growing world population and inadequate food supply
have become concerns in recent years. In an effort to increase the food
supply, scientists and farmers have proposed cultivating land areas that
are currently covered with native grasses. A variety of factors must be
studied to determine the soil best suited to growing crops as well as
what type of crops to plant.

In this activity, you will examine some of the complex variables that
interact to influence the selection of cropland and the appropriate
crops.

1)  **(Plan Investigations: Specify measurement/variables to
    investigate) & (Interpret GLOBE Data: Explain data &
    relationships)** Identify two quantitative observations about a
    study site that will give information about the growing season at
    that site. Describe how each of these factors influence seed
    germination or affect the growth of food crops. For example: How
    long is the growing season? Even if the soil is full of nutrients
    and there is adequate precipitation, if the maximum and minimum air
    temperatures create a short growing season, the crops will not
    mature.

*Answers will vary though may include (but are not limited to):*

> *The amount of yearly precipitation is important to know because the
> growing plants will need a steady supply of water during their growth
> and development.*
>
> *The amount of precipitation during the previous winter / season is
> important to know because if it was below normal the soil may be too
> dry to support germination and early plant growth.*
>
> *The soil pH and nutrients are important factors to know because
> maximum plant growth will depend on the presence of all the essential
> nutrients.*

2)  **(Take GLOBE Measurements: Use quality assurance procedures)** A
    map of Study Site T is shown below. Identify how you would collect
    samples from 8 locations (A -- H) within Study Site T. Explain why
    you created your sampling grid in this way.

(Question 2 continued)

*Answers will vary.*

*Some students may attempt to replicate the two patterns for collecting
GLOBE soil data, i.e. "the star pattern"*

![](media/image2.png){width="1.5777777777777777in"
height="1.3381944444444445in"}![](media/image3.png){width="2.8020833333333335in"
height="1.5340277777777778in"}

*or the "transect pattern"*

![](media/image4.png){width="3.817361111111111in"
height="2.272222222222222in"}

*Alternatively, the student may create a pattern that is a combination
of these collection patterns OR create a new pattern. Whatever data
collection pattern is used, the sites should be spread throughout Study
Site T so that all areas are represented.*

Table 1 shows soil measurements taken from Study Site T.

[Soil salinity]{.underline} is a measure of how much dissolved solids
are present in a sample. It is measured using a conductivity meter which
records how much electric current will pass through the sample. It is
measured in units called mmho's (milli mho's).

[Soil pH]{.underline} is a measure of the acidity/alkalinity of the
soil. pH values range from 1 -- 14. A pH of 7 is neutral. pH \< 6.5 is
acidic, while pH \> 7.5 is alkaline.

The [precipitation]{.underline} during the growing season has been
measured for the past three years at Study Site T.

3)  **(Interpret GLOBE Data: Create multiple formats to represent
    data)** Calculate the average precipitation during these three
    years. Add this value as another column in Table 1. Be sure to label
    the column and include the units used to measure precipitation.

###### **^Table\ 1:\ pH,\ salinity\ and\ annual\ precipitation\ for\ Study\ Site\ T^**

+---------+----------+-----+--------------------------------+---------+
| Soil    | ##### S  | pH  | ##### Growing season preci     | *ave.   |
| Sample  | alinity  |     | pitation for past three years  | ppt.*   |
+---------+----------+-----+--------------------------------+---------+
| A       | 6mmho    | 5.0 | 10cm 10cm 13cm                 | *11cm*  |
+---------+----------+-----+--------------------------------+---------+
| B       | 10mmho   | 4.5 | 9cm 9cm 11cm                   | *9.7cm* |
+---------+----------+-----+--------------------------------+---------+
| C       | 9mmho    | 5.5 | 19cm 20cm 21cm                 | *20cm*  |
+---------+----------+-----+--------------------------------+---------+
| D       | 9mmho    | 5.5 | 18cm 20cm 19cm                 | *19cm*  |
+---------+----------+-----+--------------------------------+---------+
| E       | 4mmho    | 5.5 | 24cm 24cm 24cm                 | *24cm*  |
+---------+----------+-----+--------------------------------+---------+
| F       | 5mmho    | 4.5 | 9cm 9cm 12cm                   | *10cm*  |
+---------+----------+-----+--------------------------------+---------+
| G       | 6mmho    | 5.5 | 21cm 24cm 25cm                 | *       |
|         |          |     |                                | 23.3cm* |
+---------+----------+-----+--------------------------------+---------+
| H       | 9mmho    | 5.5 | 18cm 19cm 20cm                 | *19cm*  |
+---------+----------+-----+--------------------------------+---------+

Table 2 shows the pH, salinity and minimum moisture needed for several
food crops that grow in the general area of Study Site T.

#### **^Table\ 2:\ pH\ and\ salinity\ tolerance^**

  -------------------- ------------ ------------------ --------------------------
  Plants               pH**^\*^**   salinity**^\*^**   Minimum moisture needed to
                                                       produce a crop yield

  Crop W               6.0          12                 16.8 cm

  Crop X               5.5          9                  17.3 cm

  Crop Y               5.5          6                  23.4 cm

  Crop Z               4.5          9                  8.9 cm
  -------------------- ------------ ------------------ --------------------------

> ^\*^ these values indicate the lower limit of pH and the upper limit
> of salinity at which plants grow and produce without damage to crop
> yields

4)  **(Interpret GLOBE Data: Explain data & relationships)** Use the
    information in Table 2 to identify where it might be possible to
    grow a Crop X in Study Site T. Describe the evidence that supports
    your conclusions.

*Answers will vary depending on how students set up the sampling pattern
in Question2. However, the information in the table should be reflected
on the map.*

  --------- ------------------ ---------------------------------------------
  *Site*    *Crop Growth*      *Evidence*

  *A*       *crop Z*           *pH too for other crops; other factors
                               support growth of Z*

  *B*       *none*             *pH too low for W, X, Y; salinity too high
                               for Z*

  ***C***   ***crop X, Z***    ***pH too low for W; salinity too high for Y;
                               moisture OK for X & Z***

  ***D***   ***crop X, Z***    ***pH too low for W; salinity too high for Y;
                               moisture OK for X & Z***

  ***E***   ***X, Y, Z***      ***pH too low for W; other factors support
                               growth of X, Y, Z***

  *F*       *Z*                *pH too for W, X and Y; salinity & moisture
                               OK for Z*

  ***G***   ***X, Y, Z***      ***pH too low for W; other factors support
                               growth of X, Y, Z***

  ***H***   ***crop X, Z***    ***pH too low for W; salinity too high for Y;
                               moisture OK for X & Z***
  --------- ------------------ ---------------------------------------------

The amount of water that is used by a crop is equal to the amount of
precipitation the area receives plus the amount of water in the soil.
This amount of moisture is referred to as evapotranspiration or ET.

ET consists of two parts, evaporation and transpiration. Evaporation is
the amount of water that evaporates from wet soil and plant surfaces
after a rain. Transpiration is the amount of water that moves through
the soil, into the roots, up the stem and moves out the leaves to the
air. The water that is involved in transpiration is part of the
photosynthesis process.

5)  **(Interpret GLOBE Data: Create multiple formats to represent
    data)** In the space below draw and label a diagram that shows the
    interactions between radiant energy, the water cycle of the
    atmosphere and the carbon-oxygen cycle of photosynthesis.

*Drawings will vary, but should include the aspects indicated in the
prompt.*

6)  **(Interpret GLOBE Data: Create multiple formats to represent
    data)** Write a description of how energy is used in these cycles.
    Include a description of the photosynthesis process in plants
    (chemical reactants, products, energy input and energy storage).
    Include a description of the energy release and energy uptake during
    the different stages of the water cycle.

*Answers will vary. Students should include the following information:*

*re: photosynthesis*

*Plants use the sun's energy to combine carbon dioxide from the air and
water from the soil to produce sugars that are used as building blocks
for all other components needed by the plant.*

*re: water cycle*

*As water vapor cools in the upper levels of the atmosphere, it
condenses and forms liquid water. When water droplet are too big/heavy
to remain suspended in the air, they fall to the earth's surface in the
form of precipitation (rain, snow, sleet, hail). Water collects on the
earth's surface in rivers, ponds, lakes and oceans. As the water absorbs
the radiant energy from the sun, some of the liquid water evaporates
into the gaseous state. This water in the atmosphere begins the cycle
over. (An additional component of transpiration may be mentioned. Water
that percolates / soaks through the soil is taken up by plant roots.
From here it may be used into photosynthesis OR it may be released as
gaseous water directly into the atmosphere during transpiration.)*

Table 3 shows the average subsurface moisture levels available to plants
during variable conditions of drought.

Table 3: Available subsurface moisture in Study Site T.

+------------------------------------------------+---------------------+
| Description of Year                            | Available           |
|                                                | subsurface moisture |
+------------------------------------------------+---------------------+
| Year with average annual rainfall              | 10.2 cm             |
+------------------------------------------------+---------------------+
| Year with below average annual rainfall        | 9.0 cm              |
|                                                |                     |
| (dry season = average -- 30%)                  |                     |
+------------------------------------------------+---------------------+
| Year with above average annual rainfall        | 11.0 cm             |
|                                                |                     |
| (wet season = average + 30%)                   |                     |
+------------------------------------------------+---------------------+

7)  **(Interpret GLOBE Data: Create multiple formats to represent
    data)** Combine the data from Tables 1 and 3 to calculate the
    EvapoTranspiration levels for a wheat crop planted in your
    recommended areas. Include additional rows in the Table 4 as needed.

(ET = seasonal precipitation + soil moisture available to plant)

Table 4: EvapoTranspiration levels for proposed wheat-growing areas of
Study Site T.

+---------------+----------------+-----------------+-----------------+
| Recommended   | ET during      | ET during       | ET during       |
| region for    | season of      | predicted dry   | predicted wet   |
| growing Crop  | average        | season          | season          |
| X             | rainfall       |                 |                 |
|               |                | (average --     | (average + 30%) |
|               |                | 30%)            |                 |
+---------------+----------------+-----------------+-----------------+
| C             | 20cm + 10.2cm  | 14cm + 9.0cm =  | 26cm + 11.0cm = |
|               | = **30.2cm**   | **23cm**        | **37cm**        |
+---------------+----------------+-----------------+-----------------+
| D             | 19cm + 10.2cm  | 13.3cm + 9.0cm  | 24.7 + 11.0cm = |
|               | = **29.2cm**   | = **22.3cm**    | **35.7cm**      |
+---------------+----------------+-----------------+-----------------+
| E             | 24cm + 10.2cm  | 16.8cm + 9.0cm  | 31.2cm + 11.0cm |
|               | = **35.2cm**   | = **25.8cm**    | = **42.2cm**    |
+---------------+----------------+-----------------+-----------------+
| G             | 23.3cm +       | 16.3cm + 9.0cm  | 30.3cm + 11.0cm |
|               | 10.2cm =       | = **25.3cm**    | = **41.3cm**    |
|               | **33.5cm**     |                 |                 |
+---------------+----------------+-----------------+-----------------+
| H             | 19cm + 10.2cm  | 13.3cm + 9.0cm  | 24.7 + 11.0cm = |
|               | = **29.2cm**   | = **22.3cm**    | **35.7cm**      |
+---------------+----------------+-----------------+-----------------+

8)  **(Interpret GLOBE Data: Explain data & relationships)** Describe a
    procedure to calculate the average EvapoTranspiration for the entire
    region that you proposed as an area for growing Crop X. Explain why
    this is the best method to calculate the ET for the region.

*Answers will vary to some extent based on the sampling pattern designed
by the student in Question 2. This may impact the reasoning used to
explain their "averaging" procedure. All responses should have some
component of mathematical averaging and may have weighting factors as
well.*

Figure 1 shows a graph of the relationship between Cumulative
EvapoTranspiration and grain yield for Crop X.

![](media/image5.pct)

Crop scientists use information like this to develop mathematical
models. Using a model derived from the experiment shown above, they can
predict a crop yield based on the amount of water available during the
growing season.

The equation that describes the graph takes the classic form (y = mx +
b) where:

y = crop yield (g/m^2^)

m = slope of the line

x = cumulative EvapoTranspiration

b = where the line intercepts the y axis.

Crop scientists and farmers can use this data to estimate the yield for
a crop when soil nutrients are not limiting and weed / insect pests are
controlled.

9)  **(Take GLOBE Measurement: Measurements are accurate and
    appropriate)** Calculate the slope of the line shown in Figure 1.

*slope of the line is calculated: change in x ÷ change in y*

*(300 -- 200) ÷ (35 --27) = 12.5*

10) **(Take GLOBE Measurements: Measurements are accurate and
    appropriate)** Extrapolate the line in Figure 1 to determine the
    y-intercept.

*y intercept = -200*

11) **(Take GLOBE Measurements: Measurements are accurate and
    appropriate)** Write a mathematical model for predicting the yield
    of Crop X using cumulative ET as the variable.

*Answers will vary to accommodate how students calculated the "average"
precipitation for the area that will grow Crop X.*

*crop yield = 200(answer to Q8) + (- 200)*

12) **(Take GLOBE Measurements: Measurements are accurate and
    appropriate)** Calculate the predicted yield of Crop X in Study
    Site T. Include calculations for:

an average moisture year

a predicted dry year

a predicted wet year

Use the space below to show all your calculations.

*Answers will vary depending on how students calculated the average
precipitation in Question 8. However, students will use the format
identified in Question 11 and substitute the area's "dry season average
precipitation" and the area's "wet season average precipitation".*

13) **(Communicate: Create reports to explain or persuade)** Write a 2 -
    3 page summary report to the farmers who work the land of Study
    Site T. Describe your recommendations for land use and the predicted
    range of Crop X. Explain how you made your decisions, why you made
    these recommendations, how you calculated the predicted yields, as
    well as any limitations or special considerations of your study and
    conclusions.