Agriculture Reference
In-Depth Information
8.6
DAY LENGTH
The length of sunlight is extremely important in crop production not only in terms of
the amount of light available for photosynthesis but also in that some plants are photo-
period sensitive. This means that they respond in their growth and reproductive habits
to the length of the day. The day length of each month for the approximate location of
each of the three farms is given in Figure 8.6. Ecuador, being on the equator, has no
difference in day length between winter and summer. On the other hand there is
almost 5
4
hours difference in day length between winter and summer in Ohio. The
Philippines being above, but near, the equator have a day-length difference of approxi-
mately 1
4
hours.
These same variations in day length December to June occur in the Southern Hemi-
sphere except that December day length is longer and that of June shorter. In either case
the effect of day length on crop production is expected to be similar.
It would be logical to assume that the amount of sunlight and its intensity might be
a controlling factor in crop production. Two situations occur that might affect the
amount of light plants receive: (1) areas of the world where there are constant
clouds, fog, rain, or other overcast conditions and (2) areas where the day length
changes from summer to winter. Vegetative production might be expected to be
adversely affected by clouds and high rainfall because clouds obscure the sun. Likewise
areas of mist and fog would be expected to have low productivity. Sunlight obscured by
these conditions does not usually adversely affect crop production. However, other
adverse effects such as lower temperatures or high relative humidity may adversely
affect crop production because of increased disease pressure. Of these, generally,
changes in day length are more important in crop production.
Areas with very low temperatures might also be expected to be unsuited to any
agricultural production. However, in northern latitudes where there are very long
days during the summer, short-season cold-tolerant crops can be grown and produce
large yields.
Day length can dramatically affect crop growth and production in plants that are
photoperiod sensitive. Many plants respond to day length, for instance, growing faster
when the day length is shorter or not flowering unless the day length is correct.
Certain varities of rice, when planted after the day length needed for flowering, will
grow a whole year before flowering and producing grain. However, if they are planted
4 months before the proper day length, they will grow, flower, and produce grain in 4
months. To avoid these types of problems, most agricultural crops, particularly the
grains, have been bred to remove or reduce photoperiod sensitivity.
8.7
LENGTH OF GROWING SEASON
Each crop needs an appropriate length of suitable weather for it to grow and produce suc-
cessfully. Generally, growing season length is considered the time between killing frost
events. However, some crops such as tomatoes are more sensitive to low temperatures
and some crops such as snow peas are less sensitive. Some crops require low
