Agricultural meteorology is the behavior of the atmosphere in relation to crops and soils. In the Great Plains, agriculture is dependent on the atmosphere in many ways. The atmosphere, in turn, links the Great Plains to other parts of the globe. This linkage is forged by air masses entering and leaving the region. These air masses provide plants with a dynamic and renewable source of carbon dioxide and water and modify other contributing factors, such as light and leaf temperature.
With no geographic barriers to the movement of Arctic air from the north or Gulf air from the south, Great Plains weather is characterized by alternate intrusions of warm and cold air, and the region therefore experiences high variability in temperature, cloudiness, humidity, and precipitation during all seasons. Temperatures are harsh during winter, particularly in the Northern Plains, where perennial plants retreat into dormancy and farmers grow annual crops, like spring wheat. Summer provides desirable temperatures for plant growth and development.
The energy required to successfully grow wheat, corn, soybeans, hay, and other crops mainly comes from abundant sunshine. Of course, without the atmosphere to absorb energy and emit a portion of it back to the earth (the greenhouse effect) the surface temperatures would be too low to support life. The atmosphere also exchanges energy through contact with the underlying surface of the ground as air masses pass through the region. This amount of energy is governed by the speed, humidity, and temperature of the air and the temperature and humidity of the underlying surface. Changes in the Plains landscape from natural grasslands to managed croplands, pastures, and windbreaks altered the disposition of atmospheric energy in the local climate. Irrigation also changes the local climate: in a dry field much of the energy goes into heating the overlying air, whereas in an irrigated field much of the available energy goes into evaporation and transpiration.
Growing season precipitation accounts for a large fraction of the annual precipitation. Soil moisture is frequently depleted during the growing season but replenished during winter and early spring, thereby providing a buffer to plants against dry weather that may occur early in the growing season. Evaporation from soils and transpiration from plants draw on stored soil moisture and increase with greater plant biomass, higher temperatures, solar radiation, and wind speed. Evaporation and transpiration decrease with increases in atmospheric humidity. Drought occurs when soil moisture falls below the amount required to meet the crops' need for water.
The main influence of the atmosphere on agriculture is the control exerted by the water and energy on crop production. The atmosphere, however, has other impacts on agriculture. For example, in wet periods the frequent formation of dew on plant leaves (leaf wetness) will increase crop damage due to plant diseases. Drought conditions favor other pests, like spider mites in corn.
Agricultural meteorologists monitor weather in order to quantify both the potential resources and possible damages associated with the dynamic atmosphere. Proper use of this information in decision making can both reduce risk and increase profit associated with agriculture, thus contributing to the goal of sustainable agricultural production in the Great Plains.
See also PHYSICAL ENVIRONMENT: Climate.
Kenneth G. Hubbard
University of Nebraska-Lincoln
Rosenberg, N. J., B. L. Blad, and S. B. Verma. Microclimate: The Biological Environment. New York: John Wiley and Sons, 1983.