![](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.

**(Taking GLOBE Measurements: Use quality assurance procedures)**

1)  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.

> **Study Site T**

*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="1.5833333333333333in"
height="1.3298611111111112in"}![](media/image3.png){width="2.7777777777777777in"
height="1.5395833333333333in"}

*or the "transect pattern"*

![](media/image4.png){width="3.8194444444444446in"
height="2.276388888888889in"}

*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.

**(Interpret GLOBE Data : Create multiple formats to represent data)**

2)  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 the precipitation.

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

+-----------+-----------------------------------------+----------------+
| Soil      | Growing season precipitation for past   | ###            |
| Sample    | three years                             | ## *ave. ppt.* |
+-----------+-----------------------------------------+----------------+
| A         | 13cm 14cm 15cm                          | *14cm*         |
+-----------+-----------------------------------------+----------------+
| B         | 17cm 19cm 18cm                          | *18cm*         |
+-----------+-----------------------------------------+----------------+
| C         | 15cm 15cm 18cm                          | *16cm*         |
+-----------+-----------------------------------------+----------------+
| D         | 18cm 20cm 19cm                          | *19cm*         |
+-----------+-----------------------------------------+----------------+
| E         | 11cm 13cm 15cm                          | *13cm*         |
+-----------+-----------------------------------------+----------------+
| F         | 14cm 16cm 15cm                          | *15cm*         |
+-----------+-----------------------------------------+----------------+
| G         | 18cm 19cm 20cm                          | *19cm*         |
+-----------+-----------------------------------------+----------------+
| H         | 9cm 9cm 11cm                            | *9.67cm*       |
+-----------+-----------------------------------------+----------------+

Table 2 shows the minimum moisture needed for a crop that grows in the
general area of Study Site T.

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

  ------------------------ ----------------------------------------------
  Plants                   Minimum moisture produce a crop yield

  Crop X                   17.3 cm

  Native Grasses           produces under variable moisture conditions
  ------------------------ ----------------------------------------------

> ^\*^ 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

**(Interpret GLOBE Data: Explain data & relationships)**

3)  Use the information in Table 1 and Table 2 to divide Study Site T
    into two areas -- the area that should be left as native grasses and
    the area that is suited to growing crops. Explain how you decided to
    divide the land into these areas. Describe the evidence that
    supports your conclusions.

    **Study Site T**

    *Student responses will vary depending on how they divided the data
    collection sites within Study Site T. Although the patterns may look
    different, the sites that are suitable for growing crops are:*

    *Soil samples A, C, E, F and H come from areas that have received
    too little precipitation in the past three years to support the
    growth and development of Crop X. These areas are best left as
    native grass growing areas.*

    *Soil samples B, D and G come from areas that have received
    sufficient amounts of precipitation in the past three years to
    support the growth and development of Crop X.*

    After planting crops in some areas of Study Site T, the plan is to
    fence off the grass-growing regions. Animals will be allowed to
    graze in these areas after the native grasses have grown to the
    appropriate stage.

    **(Interpret GLOBE Data: Create multiple formats to represent
    data)**

4)  In the space below draw and label a diagram that shows how air,
    water, and living organisms interact in the two regions of Study
    Site T -- the cropland and the grazing land.

*Answers will vary but should include drawings and labels that identify
various aspects of: the water cycle (evaporation, transpiration,
rainfall) ; the carbon-oxygen cycle (photosynthesis, cellular
respiration); and the nitrogen cycle (decomposition & decay).*

Farmers can tell the maturity of a crop in two ways. One method involves
simply looking at the plants. Figure 1 shows a drawing of a generalized
grass plant at a stage when grazing can begin. This is a stage 3.5
plant.

![](media/image5.png){width="3.088888888888889in"
height="2.109722222222222in"}

This can be a very time consuming process when the cropland covers large
areas. This process is even more difficult when the grazing site
consists of several varieties of native grasses.

An alternative method used to determine crop maturity involves a
calculation of "growing degree days" (gdd). This calculation is based on
the fact that all plants use the radiant energy from the sun to combine
carbon dioxide (CO~2~) and water (H~2~O) during photosynthesis. The
amount of energy intake is specific for each plant type. Crop scientists
use air temperature as a measure of the radiant energy available to
plants.

This is how growing degree days (gdd's) are calculated:

**[(temp max -- temp min)]{.underline} - temperature base = gdd**

**2**

The temperature base is the minimum temperature at which the plants can
grow. Cool-season grasses have a base temperature of 0C. Warm-season
grasses have a base temperature of 11C. Gdd's are added for each day
starting when the plant emerges from the ground and begins to elongate.
When the cumulative gdd reaches the appropriate number, the grass has
grown to a specified developmental stage.

Table 3 shows the growing degree days required for some native grasses
typically found growing in Study Site T. Grazing readiness occurs at
stage 3.5.

Table 3: gdd for Native Grasses

  -------------------------- --------------- -------- --------- --------- ---------
  Native Grass Variety       Developmental                                
                             Stage                                        

                             1               2        3         3.5       4

  Green Needlegrass          346             691      1037      1209      1382

  Needleandthread            290             580      859       1014      1159

  Prairie Junegrass          216             432      548       756       864

  Western Wheatgrass         297             603      954       1170      1386

  Blue Grama                 423             711      1062      1298      1530
  -------------------------- --------------- -------- --------- --------- ---------

**(Interpret GLOBE Data: Explain data & relationships)**

5)  Which grass develops the fastest?

    *Prairie Junegrass develops the fastest because it requires the
    least number of gdd to reach stage 4.*

    Which develops the slowest?

    *Blue grama develops the slowest because it requires the highest
    number of gdd to reach stage 4.*

    **(Interpret GLOBE Data: Explain data & relationships)**

6)  What is the disadvantage of beginning grazing a piece of land too
    early? What happens to the plant species that are less developed?

    *The disadvantage of grazing the land too early is that the plants
    are less mature. That means that there will be fewer plants that can
    reach the stage of producing seeds. This will decrease the growth in
    future years. Also, during the early stages before grazing
    readiness, the plant is using photosynthesis to make food for
    storage. Some of this will be stored in plant parts that are
    underground and these storage supplies will help plant growth.*

    **(Take GLOBE Measurements: Measurements are accurate &
    appropriate)**

7)  Describe a procedure to pick the best time (gdd) to begin grazing an
    area that contains the five species of native grasses shown in
    Table 3. Explain how you reached this decision.

    *One way is to find the average gdd for these five plant species. If
    you do this, the average gdd is 1089. This means that two species
    will be grazing ready, one will be ready in a few days and the other
    two are still developing.*

    *Another way is to look at the grazing area and find out which of
    the plant species is the dominant species. If one species is the
    majority of the grass in the area, then you can wait until the gdd
    is right for this plant.*

    Figures 2 and 3 shows the maximum and minimum temperatures for a
    portion of Study Site T's growing season from last year.

    ![](media/image6.png){width="4.495833333333334in"
    height="2.227777777777778in"}

    **Figure 2: Maximum Air Temperatures for Study Site T**

    ![](media/image7.png){width="4.485416666666667in"
    height="2.2131944444444445in"}

    **Figure 3: Minimum Air Temperatures for Study Site T**

    **(Interpret GLOBE Data: Explain data & relationships)**

8)  After studying the equation for calculating gdd and looking at the
    maximum and minimum graphs on the previous page, describe a
    procedure for predicting which week has the lowest gdd and which
    week has the highest gdd *without* completing all the calculations.

    *You can predict which week has the lowest gdd and which has the
    highest gdd without doing all the calculations. You do this by
    looking for the week that has the lowest maximum temperature and the
    highest maximum temperature.*

    **(Take GLOBE Measurements: Measurements are accurate &
    appropriate)**

9)  Table 4 shows you how to calculate a three day cumulative gdd.
    Choose a seven day period and complete the gdd calculations for this
    period. Show all calculations in Table 4 below.

###### Table 4: Cumulative gdd for native grasses in Study Site T

  --------------- ------------------ ---------------- --------------------------
  ^date^          (temp max + temp   ^\_^ temp base   cumulative gdd = add
                  min) 2             (-11)            numbers in column 3 after
                                                      each column 3 calculation)

  5-4             (36 + 12) 2 = 24   (24 -- 11) = 13  13 gdd

  5-5             (30 + 14) 2 = 22   (22 - 11) = 11   13 + 11 = 24gdd

  5-6             (29 + 17) 2 = 23   (23 -- 11) = 12  24 + 12 = 36gdd

                                                      

  *Calculations                                       
  should follow                                       
  the pattern                                         
  shown in the                                        
  examples above.                                     
  They may cover                                      
  any 7 day                                           
  period.*                                            

                                                      

                                                      

                                                      

                                                      

                                                      
  --------------- ------------------ ---------------- --------------------------

**(Communicate: Create a report to explain or persuade)**

10) Write a 1 - 2 page summary report to the farmers who work the land
    of Study Site T. Describe your recommendations for land use and
    describe how grazing will affect the land where the native grasses
    are growing. Explain how you made your decisions, why you made these
    recommendations, how you can predict the best time for grazing, as
    well as any limitations of your study and conclusions. (Communicate
    : Compose formal and informal reports)

Answer will vary, however student responses should include the items
specified in the prompt:

-   *recommendation for land use (item 3)*

-   *summary of how grazing affects the land (item 4)*

-   *how to predict grazing time*

-   *limitations to the study (i.e. does precipitation continue to
    follow the 3-year pattern; are soil samples taken from Study Site in
    an appropriate pattern)*