Agriculture Reference
In-Depth Information
years and crops. Variable materials are those that must be purchased repeatedly for each
new cropping season or group of animals.
10.3
SUNLIGHT
Sunlight is taken for granted by most people but is a critical input for farmers. The
amount of sunlight determines what types of crops can be grown and their quality.
For example, the east coast of Spain has a Mediterranean-type climate with warm,
dry spring weather. Dry weather means few clouds and lots of sunshine, perfect for
crops with low moisture requirements to produce sweet fruits. Grapes and oranges
are two crops that need this type of climate. Raising oranges in a rainforest climate
will produce brightly colored fruits but with low sugar contents. The high rainfall of
a rainforest requires clouds that block the sun. The result is less photosynthesis to
make sugars for sweet oranges.
Crops such as sweet corn grow in direct relation to the amount of sunlight and
warm days in the season. A calculation of growing degree days will predict when
the sweet corn is ready to pick. A company that cans sweet corn will contract with
farmers to supply sweet corn through the entire summer. Knowing how many calendar
days a variety needs to accumulate the needed growing degree days, the company can
tell a farmer when to plant. The company will then contract with farmers to plant on
specific dates so their canning plant will have a continuous supply of sweet corn
during the summer. If their calculations are off, or if the weather is bad, they will
have to stop canning for 2 to 3 days, requiring a cleaning of the entire assembly
line! A lot of expense can be avoided by accurate calculations of growing degree days.
10.4
OXYGEN AND CO
2
Carbon dioxide is needed by plants to perform photosynthesis. Oxygen is essential for
animals and humans to exist. In most cases these gases are equally distributed around
the Earth. A few commercial greenhouses practice CO
2
enrichment to increase yields of
flowers or tomatoes. These greenhouses actually purchase CO
2
in tanks and carefully
release it during the early daytime to speed up photosynthesis.
10.5
RAINFALL
Rainfall is also free but is a major limiting factor for farmers. Average rainfall is a
useful guide to determine which crops may be grown in a specific area. The numbers
shown in Table 10.2
1
are approximate but give an idea of differences between crops.
The actual rainfall needed to raise a crop depends on when the rain falls during the
crop growth cycle, the fertilizers applied, and temperature.
As a general rule, areas with less rainfall also are subject to wide variations in
monthly rainfall. Areas with higher rainfall tend to have more predictable average
