Agriculture Reference
In-Depth Information
temperatures in some parts of the year or growing season to bear fruits, and some simply
show increased productivity when the temperatures are low at certain stages of growth.
If the combination of day length and temperature are not sufficient, poor or no crop
may be produced. There are some interesting exceptions to this rule. Some crops have a
wide tolerance for day length and temperature. Cabbage can be grown in temperate and
even some tropical climates. However, it can also be gown in cold climates with very
long day lengths such as Alaska. Under these conditions the cabbage heads are very
large. Common sugarcane varieties require from 18 to 24 months to mature. Because
of the long growing time, sugarcane is typically grown where there are 365 frost-free
days during the year (there are some cold-hardy sugarcane varieties as well as varieties
that have shorter growing periods).
8.8
GROWING DEGREE DAYS
Absolute high and low temperatures may have a dramatic effect on the crop grown,
however, the number of days with temperatures needed for growth is also important
and is ascertained by determining the degree days. The degrees above some base temp-
erature each day are added to get a total degree day for that length of time the tempera-
ture is above some base temperature. The optimum temperature for a variety of crops is
given in Table 8.4. For a crop having a temperature of 108C, below which it stops
growing or is damaged, this is the lower temperature limit for this crop. A day with
a temperature of 208 would count as 108 days because it is 108 above the base tempera-
ture. For each crop and each variety there will be a different number of degree days
needed to produce a mature crop.
The first date in a year with a temperature above the cutoff is the beginning of the
count of degree days. Likewise the last day of a growing season with a temperature
above the minimum is the last day counted in determining degree days. For planning
purposes the average first and last days having the cutoff temperatures can be used
in estimating the degree days available for crop production.
T A B L E 8.4. Optimum Growth Temperatures for Selected Crops
Optimum Temperature
(8C)
Temperature (8C) for Maximum
Yield
Crop
Wheat
15 - 20
15 - 20 (grain yield and grain
weight)
Potato
18 - 20
5 - 20 (tuber production)
Pea
14 - 18
15 - 25 (flowering)
Sugar beet
17 - 22
20 - 22 (sugar production)
Barley
17 - 22
22
Cabbage
15 - 24
10 (hasten flowering)
Apple
20 - 24
15 - 20 (pollination)
Strawberry
5 - 26
14 (favor flowering)
