Thermal conditions

Normal growth and development of vegetable plants and the formation of a productive part are possible only at a certain temperature. The main source of thermal energy for plants is solar radiation, as well as organic matter introduced into the soil manure and compost, passing through various stages of decomposition, also secrete thermal energy. Different vegetable plants react unequally to the temperature regime, which largely depends on their origin. Vegetable plants and even varieties of the same culture can be divided into five groups according to their relation to heat:

1. Frost and winter-resistant perennials - sorrel, rhubarb, horseradish, asparagus, lovage, tarragon, perennial onions, garlic. Plants of this group during the vegetation period are able to carry frosts up to -8-10 ° C in the spring and autumn, and their winter organs( roots, rhizomes) cover the winter well. Due to the ability to increase the concentration of cell sap in wintering buds at rest, winter-resistant cultures hibernate in the open ground with shelter, frost-resistant can withstand severe frosts( -15-35 ° C) without shelter.

In plants of this group, growth begins at a temperature of 1 ° C, but most vigorously goes at 15-20 ° C.

2. Cold-resistant - two-year-old cabbage plants - root vegetables, lettuce, vegetable peas, beans, dill, spinach, onions. The cultures of this group can carry temperatures of -2-1 ° C for a long time, and frosts up to -3-5 ° C for several days. Seed germination of cold-resistant crops begins at 2-5 ° C.The optimum temperature for the onset of intensive vegetation is close to 17-20 ° C.The temperature of 20 ° C is optimal for the development of the crops of this group;at a temperature above 25-28 ° C there is a marked inhibition of the plant, at a temperature above 30 ° C their growth stops. This is due to the fact that in cold-resistant plants the intake of organic matter from assimilation becomes equal to the expenditure on respiration at a temperature of 30-32 ° C.Thus, they do not accumulate organic substances, since much energy is expended on breathing.

Cold-resistant crops are adapted to such conditions when the soil temperature is 2-3 ° C below the air temperature. At the same time, the root system develops better, the resistance of plants to unfavorable conditions, pests and diseases increases.

Frost-, winter- and cold-resistant crops form flowers and fruits only after passage of vernalization - a certain period of stay in conditions of low temperatures( from 3 to -15 ° C).

3. Moderately cold-resistant - potatoes. The plant at his death at 0 ° C, as in demanding crops, and growth and tuber formation are best at a temperature close to optimal for cold-resistant plants, which is 15-20 ° C, at 10 ° C, growth is noticeably slowing down.

4. Heat-loving - tomatoes, peppers, aubergines, pumpkin, beans, cucumbers, zucchini, squash - do not tolerate even short-term frosts. The optimum temperature for them is 20-30 ° C.At temperatures slightly below 0 ° C, they die. The compensation point for them is close to 40 ° C.Demand of heat-loving crops to heat varies during certain periods of life. Heat-loving plants begin to germinate at a temperature of 13-14 ° C, but the main vegetation occurs at 25-30 ° C.At the beginning of growth, these plants can withstand short-term cooling to 12 ° C, but at prolonged low temperatures, their roots slowly absorb nutrients from the soil, the leaves weakly assimilate carbon dioxide, and at temperatures below and below, chlorophyll in the cells is destroyed, the plants pale and turn yellow, there is a serious inhibition of growth. Lowering the temperature during fruiting to 14 ° C, especially at night, adversely affects fruit formation, as fruits grow mainly at night, at this time there is an increased outflow of organic substances from the leaves. Cultivation of heat-loving plants in the middle zone of Russia requires the use of special agrotechnical techniques. Heat-loving crops most often do not ripen because of a lack of heat in the open ground. The prolonged cold weather damages plants more than a prolonged drought. Night cooling in summer and early autumn sharply reduce the vegetative period of heat-loving crops. During fruiting, the optimum temperature is 25-32 ° C.Higher temperatures adversely affect plants, they can be affected by various diseases. To improve the thermal regime, heat-loving crops are placed on the south and south-west side of the site, grown on ridges, mulched with a film, protected by wings from tall plants or grown in sheltered soil.

	Temperature	Fatal
Temperature
	seed swelling seed	16-23	crop formation 15-17	for shoots in spring -2-3	for adult plants in autumn
Cabbage to the head	2-3	-8-10
Carrots	4-6	18-25	15-25	-2-3	-3-4
Beetroot tableware	5-8	20-30	18-25	-1-2	-2-3
Onion	2-5	18-25	15-25	-2	-
Radish	1-2	15-25	14-18	-2-3	-5-6
Radish	1-2	15-20	15-20	-2-3	-4-5
Spinach	2-3	15-18	12-17	-4-6	-6-10
Salad	2-3	10-20	12-20	-2-4	-4-6
Beans	8-10	18-22	20-32	-0,5	-1
Tomato	10-12	25-30	20-27	3-5	-1
Pepper	14-16	25-30	25-30	5-6	-1
Eggplant	14-16	25-30	25-30	5-6	-1
Cucumber	14-16	25-30	22-28	6-8	2-3
Pumpkin	12-15	20-25	22-30	5-7	2-3

5. Heat-resistant plants - melon, watermelon, corn. The need for warmth in them is about the same as for heat-loving plants, but at 40 ° C, and sometimes at a higher temperature, heat-resistant plants are able to accumulate organic matter and develop without sacrificing the plant itself and its fruits.

The vital processes that occur in plants depend on temperature: absorption of carbon dioxide( photosynthesis), water intake, absorption of nutrients from the soil, respiration, evaporation of water( transpiration), movement of nutrients from roots to leaves, kidneys and fetuses, andplastic substances from the leaves to the roots.

The need for plants in the warmth in different phases of vegetation is not the same.

During the period of growth and development, the requirements for temperature conditions for vegetable plants are changing. During seed swelling, a low positive air temperature may be sufficient, for germination a higher level is necessary, and at emergence, a lower temperature. Therefore, in the sheltered ground at elevated temperature and lack of light, stretching of plants is often observed. During the flowering and fruiting period, the temperature should be increased. The minimum temperature for germination of cold-resistant crops is 1-5 ° C, for thermophilic crops - from 14-15 to 16-17 ° C.Increasing the temperature to 25-30 ° C accelerates germination, which leads to rapid consumption of seed nutrients for growth processes and respiration. Therefore, when growing seedlings of cold-resistant crops in greenhouses and greenhouses, the temperature is reduced to 8-10 ° C, for heat-loving crops - up to 14-15 ° C.Under these conditions, the root system continues to develop, since for its growth the soil temperature can be 3-4 C lower than air. After 5-7 days, the temperature is gradually increased to 15-20 ° C for cold-resistant and to 20-24 ° C for heat-loving crops. The high temperature when growing seedlings causes an increased expenditure of nutrients on respiration, while their inflow due to assimilation with a very small cotyledon size and poor development of the roots is limited. Reduced temperature inhibits the growth of the underground part, prevents drawing

Optimal and critical temperatures for various types of vegetable crops, ° С

shoots and creates more favorable conditions for growth and formation of the root system. To accelerate the formation of the assimilation apparatus and the accumulation of organic matter with a well-developed root system, an optimum temperature is required for each of the plant groups. High temperatures when growing seedlings, especially at night, have a harmful effect on the growth and development of plants: they are greatly weakened, subsequently grow poorly, give a late and low yield. Since at night plants do not consume energy for photosynthesis, their need for warmth during this period of the day decreases. In addition, a decrease in temperature reduces the consumption of nutrients on the respiration of plants. Therefore, at night, the air temperature should be 5-7 ° C lower than the daytime.

To increase the resistance of plant seedlings to a decrease and temperature drop and even to short-term spring frosts, it must be hardened, that is, grown at a lower temperature. For tempering seedlings, this temperature is important to maintain immediately after emergence to avoid stretching. Seasoned seedlings can be planted at an earlier time than uncombined.

Along with the creation of favorable environmental conditions, it is important to adapt the plants themselves to unfavorable conditions by tempering seeds and seedlings.

The stability of heat-loving plants to a reduced temperature can be improved to some extent by agrotechnical methods. So, when the swollen seeds of these crops are exposed to temperatures below 0 ° C for 2-3 days or alternating temperatures( 06.00 - 15-18 ° C and 18.00 - to 2 ° C) for 5-6 days germination begins at a lowertemperature, and shoots acquire some resistance to a decrease in temperature.

The optimum thermal regime can be maintained in hotbeds and greenhouses, it is more difficult to regulate it in the open ground. The type of soil is important here. Light sandy loam or light loam is better heated during the day and less cooled at night. Heavy clay and peat soils are cold and suitable for cultivation of cold-resistant crops. To create a favorable thermal regime for vegetable crops, it is necessary to select areas well protected from cold winds and having a southern slope: they are 2-3 ° C warmer than on the northern slope, and the conditions for plant growth and development are more favorable. The thermal regime of in the open ground is regulated by various agrotechnical methods. For the growth of heat-loving plants, early vegetables and seedlings, ridges are built, high ridges that warm up faster and better than a flat surface of the soil. An effective technique regulating the temperature of the soil is mulching - a continuous or tape coating of the soil with polymer films, special paper or organic materials. So, when mulching, the inflow and accumulation of heat in the soil can increase up to 40-46 %, and the average daily temperature of the root layer will increase by several degrees compared to the undimmed surface. Significantly improves the thermal conditions of the creation of rocking strips, located across the direction of the prevailing winds, from tall one-year fast-growing plants. To do this, use corn, sunflower, peas, beans and potatoes. Rocking crops are used in the cultivation of cucumbers, melons, tomatoes, peppers, eggplant and beans.

Thermophilic crops are grown on sections between the wings. The distance between the wings should be 4 times their height. The air temperature in the intercrystalline space is higher by 1.5-4 ° C, because the cooling of plants decreases due to the decrease in wind speed. The wings contribute to an increase in the relative humidity of the air and the preservation of moisture in the soil, as well as rocking crops protect the main crops from overheating.

Vegetable plants also respond to the duration of the warm period. With a prolonged drop in temperature, the vegetative period increases, the growth of shoots and the ripening of the fruit slows down and, as a rule, their quality deteriorates.

In conditions of open ground, vegetable plants can be damaged by frosts, which are observed in the northern regions until June.

Smoke curtains are used to control frosts on plots: burn special smoke bombs or wet smoke-generating materials( brushwood, rubbish, sawdust, half-rotten straw, foliage).Smoke, preventing the loss of soil moisture, contributes to an increase in the temperature of the surface layer of air.

To reduce the harmful effects of low temperatures on plants, pre-frost irrigation is also used, which increases the thermal conductivity and heat capacity of the soil. In strong frosts, an additional night sprinkling is carried out. As a result of watering, heat from the lower layers of the soil and the surface layer of air enters the surface, raising the temperature of the upper layer of the soil and the surface air layer. Wetting plants reduces their hypothermia. Sprinkling should continue until the daytime temperature increases.