The temperature is the most important climatic factor affecting the life of the agricultural crop. The temperature plays an essential role in photosynthesis and in the growth and maturity of the crop. Each agricultural crop has three thermal limits for growth that are the lowest, most appropriate, and highest for each stage of its growth, from germination to the stage of the emergence of the plant to the surface of the earth growth and ending with maturity, in other words, each crop has a minimum growth temperature known as zero temperatures of growth and maximum growth temperature growth, so if the temperature drops below or exceeds the maximum temperature, it will stop. represent the best thermal conditions to increase the speed of plant growth where Optimum Growth Temperature for a crop of growth, and in return for each agricultural crop a more appropriate (optimal) temperature for growth Cardinal The growth rate of the crop gradually decreases when the temperature drops or rises below that optimal level. The three thermal limits are called the basic heat limits for agricultural crop growth. These basic boundaries vary according to crops, where they are low for winter crops such as wheat and barley and high for summer crops such as corn and rice. Growth Temperature
The table below represents the basic heat limits for the growth of winter and summer agricultural crops in general.

(Cardinal growth temperature)
Crop type	Minimum growth temperature (Zero temperature  of growth)	Optimum growth  temperature	Maximum growth temperature
winter crops	C°  6 – 0 32 – 42  F	25 – 31  C° 77 – 87.8  F	31 -37  C° 87.8 – 98.6  F
summer crops	15 – 18  C° 59 – 64.4   F	31 – 37  C° 87.8 – 98.6  F	40 – 44  C° 111.2 – 121 F

Each plant needs to be life-matured to a certain number of thermal units that must accumulate during its lifetime above "zero growth" and these units are called the collected heat  Accumulated Temperature

On this basis, the combined temperature can be defined as the sum of units or temperatures that accumulate above the lowest daily average temperature in which plants can generally grow. In the opinion of most researchers, it is 6 m. Heat collected for one day, week, month, or otherwise can be calculated, while the combined temperature for the growing season is the sum of temperatures collected in all months covered by this season. On this basis, each plant needs to be life-long for a certain number of days and also a certain number of daily thermal units, knowing the total daily thermal units G.D.D growing degree day is necessary to determine the growth periods, maturities, and harvesting of cultivated crops and can help farmers to schedule the use of pesticides and control the bush, and the estimation of the combined temperature of the growing season is very important in determining the type of yields that can be grown in a particular region. The first Zero Temperature of Growth On this page, we present the monthly combined temperature values of network stations distributed in different regions of the country by including two zero-growth values.
(0°C) and the second (6°C) where the monthly combined heat represents the total daily combined temperature values for that month, where the following is calculated:
Monthly pooled temperature = total daily pooled temperature per day of the month.
Daily combined temperature = average daily temperature - zero growth temperature (0 or 6)
Average daily temperature = (great daily temperature + minimum daily temperature) / 2 *
The day when the average temperature is less than zero growth, its aggregate temperature is zero.