# Growing Degree Days and Relative Humidity Worksheet by panniuniu

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```									Growing Degree Days and Relative Humidity Worksheet C. Kohn, Waterford WI
Name:                                                          Hour                Date:

Date Assignment is due: tomorrow (5-13)                 Why late?
Day of Week    Date                            If your project was late, describe why

Directions: The first questions of this worksheet will deal with Growing Degree Days (GDD). The GDD is the amount of
time necessary for a specific crop to mature. Because heat and sunlight can vary the time necessary for a plant to
mature, GDD can be a more useful measure than the number of days to maturity. Be sure to show all work! Attach
scratch paper if needed. GDD is calculated by taking the average of the day and subtracting the base temperature
needed for growth for that plant. In other words, GDD =

[Daily High – Daily Low] - Base Temp
2

1. Imagine the high for today was 70 and the low was 50. If the Base Temp necessary for corn is 50o F, what is the
GDD for corn for today? Be sure to show your work!

2. If corn needs a total of 2450 GDD to mature, how many days would it take for corn to reach maturity if each day
had a high of 70 and a low of 50? Show your work with your answer
Avg   Avg
Month Low   High
April    39    61
3. Monthly averages for a hypothetical area are shown to the right                                          May      49    68
a. If you planted your corn on May 1st, how many GDDs would it receive per                              June     60    81
day in May? How many GDDs would it receive for the entire month?                                   July     62    86
Aug      61    85
Sept     51    75
Oct      39    62
b. How many GDDs would your corn receive in June - Sept per day? How
many per month?
i. June                                           iii. Aug

ii. July                                           iv. Sept

c. On what day would your corn mature if it needs 2450 GDD? (note – you’ll need to determine the GDD
for each month. See the example on the back side of this page.
Example Problems
Wheat needs 1600 GDD to reach maturity. The Base Temp for Wheat 40o F.

1. On a day with 70o F for a high and 50o F for a low, the average temp would be 60o F
([High + Low] / 2 = Avg Temp  [70+50] = 120. 120/2 = 60)

2. If a 70 high/50 low day has an average temp of 60o, then for wheat there would be 20 GDD per day
(Avg Temp – Base Temp = GDD 60 – 40 = 20 GDD)

For monthly averages…
3. An average day in May has a high of 68 o and a low of 44 o. The overall average would be (68+44)/2  112/2 =
56

4. Average May temp = 56; Base temp for wheat = 40; 56 – 40 = 16 GDDs for wheat on an average day in May.
a. There are 31 days in May, each with an average of 16 GDDs  31 days x 16 GDDs = 496 GDDS for May

5. June has an average high of 78 and a low of 55; Average temp = 66.5; Average GDD for a single June day is 26.5
a. 30 days in June  30 days x 26.5 GDD = 795 GDDs total for June on average
b. Total Average GDD for May and June  496 GDD + 795 GDD = 1291 GDD for May and June

6. July has an average high of 82 and a low of 60. Average temp = 71; Average GDD = 31
a. 31 Days in July; 31 x 31 = 961 GDDs
b. However, if we already have 1291 GDDs between May and June, the wheat will reach maturity (1600
GDDs) before the end of July.
c. As of June 30th, the wheat will have received 1291 GDDs. 1600 GDDs are needed for maturity
d. If 1600 GDDs are needed for maturity, 309 GDDs are needed as of June 30th
e. If the average July day has 31 GDDs, it would take roughly 10 more days to reach the 309 additional
GDDs needed on June 30th (31 x 10 = 311).
f. Therefore, we can expect the wheat to reach maturity on July 10th.

To figure out these problems, use the following steps –
a. Determine the Base Temp for your crop (e.g. corn has a base temp of 50; wheat has a base temp of 40)

b. Determine the average temperature for a day in a particular month (e.g. if May has a high of 68 and a low of 44
on average each day, then the overall average would be (68+44)/2 = 56

c. To find the daily GDD, subtract the base temp for the crop from the average daily temp for the month.
E.g. Avg May Day – Wheat Base temp  56 – 40 = 16 GDDs

d. To find the GDDs for each month, multiple the daily average GDDs times the number of days in the month
E.g. May has 31 days each with an average GDD of 16. 31 x 16 = 496 GDDs for the month of May (on average)

e. Determine the maturity date for the crop by adding GDDs monthly (e.g. 496 GDDs for May, 795 GDDs for June,
etc.) until you are near the total for that crop (e.g. 1600 GDDs to maturity for wheat). Then determine the GDDs
day by day until you reach or just barely surpass your total.
4. Climate change is predicted to increase the average global temperature by 2o. If this were to occur, by how
much would the maturity time for corn change? With 2o added to the high and low, calculate the new expected
date of maturity for corn. Show your work below. Keep the baseline temp of 50o for corn and the May 1 planting
date.
a. GDDs for May (at 2o higher):                                                                New New
Month        Low   High
April           41    63
May             51    70
b. GDDs for June:                                                                June            62    83
July            64    88
Aug             63    87
Sept            53    77
c. GDDs for July:                                                                Oct             41    64

d. New corn maturity date

5. Your cousin is getting married on July 1st and would like to have sunflowers at her wedding here in Waterford.
She is well aware of your amazing gardening skills and has asked if it would be possible for you to grow her
sunflowers that would be ready on July 1st. Keep in mind that…
a. Sunflowers have a base temperature of roughly 45o F
b. Sunflowers require 2310 GDDs to reach full maturity
c. Assume average temperatures for each month are…
i. April – High: 56; Low: 34
ii. May – High: 68; Low: 44
iii. June – High: 78; Low: 55
iv. July – High: 82; Low 60
v. August- High 80; Low 58
vi. September – High 72; Low 49
d. Assume the earliest planting is April 1st. Is it possible to have fully grown sunflowers by this wedding
date? Answer by stating the earliest date that the sunflowers will reach maturity. Show your work.
Relative Humidity is a measure of how saturated the air is with water vapor. Relative humidity changes with
temperature; higher temperatures can hold more moisture in the air than lower temperatures. In the table below, you
can see that as the temperature increases, the Absolute Humidity (or 100% Relative Humidity) increases. Relative
humidity is simply the amount of vapor in the air as a percentage of the maximum possible. For example, 50% RH at 68o
F would be 8 or 9 g/m3. At 50o F, 50% RH would be 4.7 g/m3.

Temperature           Absolute Humidity
(C/F)                 (g/m3 )                        6. The weatherman says that the temperature is 77 o F with a relative
humidity of 75%. How many grams of water vapor is in a cubic meter of the
0o C/32o F            4.8                        air? (in other words, what is the g/m3 of water vapor at 75% RH at 77o?).
5o C /41o F           6.8                        Show your work.

10o C /50o F          9.4

15o C /59o F          12.8

20o C /68o F          17.3

25o C /77 o F         23.0
7. It is a hot, muggy, 86 degree day. Currently, the air has 27 g/m3 of
o       o
30 C /86 F            30.4                       water vapor.
a. What is the relative humidity? Show your work

b. If this same air is pulled into a building’s ventilation duct, what would the relative humidity be inside the
building if it was air conditioned to a 68o temperature?

8. Which is likely cause more transpiration in a plant –
a. 81% RH on a 59o October Day,
b. 71% RH on a 68o April Day
Show your work below! Remember that the relatively drier air will cause more transpiration. In
other words, the air that has the most moisture yet to be gained will cause the most
transpiration

For example, 50% RH on a 50o day means that 4.7 g/m3 can still be absorbed; on the other hand,
50% RH on a 59o day means that 6.4 g/m3 can still be absorbed, causing more transpiration.

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