The crops to be grown, the agricultural operations and agricultural patterns are closely influenced by the prevailing temperature conditions of the region. The agricultural scientists have proved that each crop has a specific zero below which it cannot grow. There is also an optimal temperature in which the crop is at its. Greatest vigour. For each of the functions of crop life, weather germination, foliation, blossoming or fructification a specific zero and optimum can be observed in the temperature.
The impact of temperature on agricultural patterns may be seen from the fact that the northern limit of the regions in which the date- palm bears ripe fruit coincides almost exactly with the mean annual isotherm of 19° C. The essential factor in the limit of grape orchards seems to be the temperature in summer, for the grape ripens only in those countries in which the mean temperature from April to October exceeds 15° C. Similarly, it has been calculated that maize ripens at the period of the year when the sum of the daily maximum temperatures has reached 2500° C.
In general, crops like barley, rye, oats and winter wheat perform well when the mean daily temperature ranges between 15° C and 25° C. Contrarily, tropical crops like cacao, coffee, spices, squash, dates, rubber, and tobacco require high temperature throughout the year, while crops like peas, gram, lentil, wheat, potato, mustard, rapeseed, linseed, lucern and bar seem require relatively warm temperatures during the growing and ripening periods and low temperatures (around 20° C) during the growth and development stage.