Plant Growth in Desert Environments
The word desert implies a deficiency of rainfall as the basic characteristic of desert environments. However, the amount of rainfall cannot serve as an adequate measure of a desert unless the amount of rain is related to its effectiveness. The effectiveness of rainfall depends on its seasonal distribution, the rate of evaporation, the nature of the soil, and the vegetative cover. The rate of evaporation is determined by temperature, air humidity, and wind movement. A desert environment is defined as one in which, for the greater part of the year, rainfall is less than the potential evaporation plus water loss from plants. A number of attempts have been made to classify the different types of dry (desert) climates, generally based on the amount of rainfall and its effectiveness. None of the classifications that have been developed is ideal in the sense that it is simple and complete, and that climatic factors relate satisfactorily to natural vegetation, to soil types, or to land use. The Köppen System of Climate is the most generally accepted system and it is based mainly on the relation between rainfall (amount and distribution) and temperature. It assumes that: (1) the higher the temperature, the greater the amount of precipitation that will still result in the same degree of aridity, and (2) relatively less precipitation is needed if it is concentrated during the cool season, more is required if distribution throughout the year is uniform, and the highest requirement is associated with precipitation that is concentrated in the warm season (Arnon 1972).
KeywordsZinc Phosphorus Magnesium Cobalt Manganese
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