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Horticulture Principles and Practices

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4.1 CLIMATE, WEATHER, AND HORTICULTURE<br />

Climate is a combination of aboveground environmental factors—temperature, moisture,<br />

sunlight, <strong>and</strong> air—<strong>and</strong> is characteristic of a region. It determines what crops can be cultivated<br />

in a given area. Some regions receive 0 to 25 centimeters (0 to 9.9 inches) of precipitation<br />

per annum <strong>and</strong> are said to be arid, or dry, whereas other regions may receive<br />

75 to 100 centimeters (29.5 to 39.4 inches) of precipitation <strong>and</strong> are called humid regions.<br />

The immediate environment of plants is called the microclimate. This environment plays<br />

a role in plant processes such as evaporation (loss of moisture from any surface) <strong>and</strong><br />

transpiration (loss of moisture by plants) <strong>and</strong> also in the incidence of disease.<br />

Weather is the composite effect of the interplay of temperature, precipitation, wind,<br />

light, <strong>and</strong> relative humidity as it pertains to a specific locality. These weather factors are<br />

dynamic, having daily, weekly, monthly, <strong>and</strong> seasonal patterns of variation. These local<br />

patterns are repeated year after year, creating the climate of the specific area. Regional<br />

weather patterns are affected by factors including altitude, latitude, <strong>and</strong> geographic<br />

features such as mountains <strong>and</strong> large bodies of water. The higher you go, the cooler it<br />

becomes. Oceans <strong>and</strong> large lakes moderate temperature extremes of nearby l<strong>and</strong> masses.<br />

Vegetables <strong>and</strong> fruit crops are delicate <strong>and</strong> require stable climates for optimal production.<br />

They are grown on the leeward side of large lakes; grain crops, which perform well under<br />

drier <strong>and</strong> less stable climatic conditions, are grown on the windward side. Large bodies<br />

of water also store heat in fall <strong>and</strong> are cold reservoirs in spring. The stored heat has a<br />

warming effect on the l<strong>and</strong> around the lake by delaying the onset of frost on<br />

the leeward side (Figure 4–1). Valley floors are colder than hillsides because cold, dense<br />

air sinks to lower levels. A belt of warm air above the cold air in the valley is called<br />

a thermal belt <strong>and</strong> is a region where conditions are conducive to fruit production<br />

(Figure 4–2).<br />

4.2 ABOVEGROUND ENVIRONMENT<br />

The aboveground environmental factors may be classified into two types—abiotic<br />

(nonliving) <strong>and</strong> biotic (involving living organisms).<br />

4.2.1 ABIOTIC FACTORS<br />

The abiotic factors in the environment are air, water, temperature, <strong>and</strong> light.<br />

Windward<br />

Leeward<br />

FIGURE 4–1 The role of<br />

large bodies of water in altering<br />

the climate.<br />

Large body of water<br />

Wind<br />

Less stable climate<br />

Drier<br />

More stable climate<br />

Moist<br />

Suitable for<br />

grain crops<br />

Suitable for<br />

fruits <strong>and</strong> vegetables<br />

4.2 Aboveground Environment 95

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