Physiological processes in a plant proceed only with a certain amount of heat. At low temperatures, the plants stop growing. The need for heat is different not only in plants belonging to different families, but also in the same culture in certain phases of development. The optimum temperature for the growth and development of most crops
- 20 .. .25 ° C. At a temperature slightly above 30 ° C, inhibition of growth processes is observed, and when it increases to
- 50 … 52 ° C plants die.
To complete the full cycle of plant development, a certain amount of active daily average temperatures (above 10 ° C) for the growing season should be obtained. According to this indicator, they are divided into heat-loving, whose seeds germinate at a temperature of 8 … 12 ° C, need a sum of active air temperatures of 3000 … 4000 ° C and cold-resistant, whose seeds germinate at a soil temperature of 2 … 5 ° C and for the entire growing season they need the sum of active air temperatures of 1200 … 1800 ° C.
Such thermophilic cultures as cucumber, tomatoes, melons are damaged, and sometimes completely die off at positive temperatures of +3 … 7 ° С. Buckwheat, corn, and potatoes are somewhat more resistant to low positive temperatures. Oats, barley, rye, wheat, beets, cabbage are cold-resistant crops and at positive temperatures of 3 … 5 ° C they show no signs of damage and productivity is practically not reduced. Among cold-resistant crops, frost-resistant ones are able to tolerate relatively low temperatures (from -18 to -24 ° C and below). This group of crops includes winter cereals, perennial grasses.
Like light, heat is hardly regulated in natural conditions. Only the thermal regime of the soil is subject to minor regulation. With the help of irrigation, early spring harrowing, loosening the soil, planting forest belts, snow retention, mulching and other techniques, it is possible to regulate the thermal regime of the soil.
18. The need of plants for heat, ° C
|Emergence of seedlings||Frost
round, ° С
|The sum of the active temperatures during the growing season, C|