Agriculture Reference
In-Depth Information
For countries such as the Philippines and Ecuador where two of our three farm
examples are located the temperature never goes below 108C, and thus the number
of degree days is generally a mute point. For crops that require a certain number of
cool or cold days to produce a crop, such as apples, the number of cool days and the
coolness can be calculated in a similar way. Thus, while the Philippines are not suitable
for apple production, Ohio in the United States is ideal.
8.9
HUMIDITY
Humidity refers to the amount of water in air and is commonly reported as the rela-
tive humidity. Dew point is also related to humidity, being the temperature at which
water condenses out of air. The lower the relative humidity and dew point the dryer
the
air.
High
humidity
and
high
dew
point
both
indicate
conditions
favorable
to precipitation.
The relative humidity has a pronounced effect on crop water needs and drying
before harvest. Hot, dry, low-humidity climates will require more water for crop pro-
duction, usually in the form of irrigation, than will humid, cool, or hot climates.
Drying and water loss will be even more pronounced if there is air movement as
wind or even a slight breeze, and this may necessitate irrigation. Drying of a mature
crop will be faster in hot low-humidity climates.
Some crops will have higher pollination rates and grain production under humid
conditions. The humidity of an area can thus have a significant effect of the success
of certain crops. In low-humidity regions this may partially be offset by irrigation, par-
ticularly by sprinkler irrigation, at the time of flowering. However, humidity is a factor
in crop production in all areas of the world.
8.10
ADVERSE WEATHER CONDITIONS
All plants and animals are susceptible to adverse weather conditions, as illustrated in
Table 8.5. Adverse weather conditions include intense high rainfall, most often associ-
ated with high wind. High-intensity rainfall will cause soil erosion and scarring of land,
as seen in Figure 8.17 (learn more about erosion in Chapter 9). Erosion removes the
most productive, high-fertility soil, leaving the field or area less productive. Keeping
the soil covered with either plant residues or growing plants controls water erosion.
High rainfall can also decrease crop production, as noted in Table 8.5.
High winds such as those in typhoons, hurricanes, and tornados can do both phys-
ical and production harm to crops. Physical damage might be caused by breakage of
limbs or stems. Breakage can be caused by the winds themselves and by material
carried in the wind. In some cases this may be as simple as sand scarring of leaves.
In other cases it may be due to flying objects hitting the plants. Breakage of plant
parts may cause loss of productivity because of loss of fruiting plant parts. However,
for many crops lodging is a primary cause of harvesting problems associated with
high winds (Fig. 8.16).
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