Classification of vegetable crops by their heat requirements

AND DEVELOPMENT OF VEGETABLE CROPS According to their heat requirements, vegetable plants can be divided into five groups. 1. Frost-resistant and winter-hardy plants. This group includes perennial plants: sorrel, rhubarb, asparagus, horseradish, tarragon, Welsh onion, chives, tree onion, Egyptian onion, leek, and garlic. These plants withstand winter frosts under snow cover thanks to the nutrient reserves in their rhizomes and roots, which increase the concentration of cell sap in overwintering buds. 2. Cold-resistant plants: cabbage, carrot, parsley, parsnip, beet, radish, daikon, turnip, rutabaga, onion and shallot, and leafy vegetable plants (leaf and head lettuce, Chinese leafy cabbage, spinach and Swiss chard, dill, leafy parsley, leafy and stalk celery, coriander, watercress, mustard greens, borage), as well as legumes (garden peas, beans). These plants can tolerate light frosts at the seedling stage. Their seeds can germinate at a temperature of 3—5° C, but emergence is delayed for a long time. The most favorable temperature for seed germination and seedling emergence is 18—20° C. Therefore, although the seeds of these crops can be sown as soon as the soil is ready for sowing, it is better to sow pre-germinated seeds into warmed soil, covered in advance with film, to ensure faster emergence. 3. Intermediate position is occupied by potato — it grows better in cool weather but does not tolerate frosts. To obtain early produce, seed tubers of early-ripening cultivars should be pre-sprouted. 4. Heat-demanding plants: cucumber, summer squash, pattypan squash, tomato, eggplant, pepper, physalis. These plants do not tolerate prolonged temperature drops even below

+ 10° C. Their seeds start to germinate only at 13—14° C, but seedlings appear slowly at this temperature. The most favorable temperature for emergence is 25—30° C. In the conditions of the Non-Chernozem zone, these crops should be grown either in a greenhouse or in the field using transplants. Heat-demanding crops grown from transplants are subjected to hardening at both the swollen seed and transplant stages to increase plant resistance to low temperatures and improve their vitality. For this, swollen seeds are kept for two to three days at a temperature below freezing and then sown. When hardening at the transplant stage, the temperature in the greenhouse is lowered for a few days to +6—8° C upon emergence, and then raised in accordance with the requirements of the crop, but the temperature is necessarily lowered at night. This is necessary to strengthen the growth of the root system and prevent plants from stretching. During the fruiting period of these crops, the plants' heat requirements increase. 5. Heat-tolerant plants — green beans, sweet corn, watermelon, melon, pumpkin. These plants tolerate such high temperatures at which the plants of the fourth group stop growing. Plant response to light. Cucurbits, nightshades, and legumes are most demanding of light intensity. Less demanding are cabbage, root crops, onions, and leafy vegetables. Vegetables such as green onions, sorrel, and rhubarb can tolerate some shading. Plants are particularly demanding of light when growing transplants. Low light and high temperature lead to a decrease in assimilation, i.e., the ability of plants to create and accumulate organic matter using the solar radiant energy. As a result, the quality of transplants of light-demanding plants decreases; they become pale and elongated. The period after emergence is the most critical moment when growing transplants. Seed nutrients are already exhausted, and at this time, plants have the greatest need for light; that is why overcrowding of crops must not be allowed. When growing transplants, the root system is... Soil moisture requirements. The most demanding of moisture are early-ripening leafy vegetables: lettuce, Chinese cabbage, spinach, radish, onion, cucumber, cabbage, turnip, radish, rutabaga. As a rule, these vegetable plants have a weakly branched and shallow root system. A large leaf surface of some vegetable crops (cucumber, cabbage) also contributes to heavy moisture evaporation. Carrots and parsley are less demanding of moisture, as they have a powerful root system and use moisture sparingly for evaporation. Although beets have a powerful root system, due to high moisture consumption for evaporation, they are more demanding of moisture than carrots and parsley. Tomatoes grown from transplants have a powerful root system that permeates every centimeter of the soil and use significantly less moisture for evaporation than cabbage, so their water requirement is lower. However, when forming the bush after removing side shoots (suckers), the power of the root system decreases, and the more so, the fewer fruiting shoots remain. As a result, the water requirement of such plants increases accordingly, especially the denser the plant spacing. Most resistant to soil moisture deficit are watermelon, melon, pumpkin, sweet corn, and beans. The pumpkin has the most powerful root system, but its evaporating surface is also huge, so the pumpkin responds gratefully to irrigation. The water requirement of vegetable plants during different periods of the growing season is not the same. Thus, high soil moisture is necessary during seed germination, when planting transplants, during leaf growth, especially in onions, during head formation in cabbage, and during the fruiting period of cucumbers and tomatoes. Legumes are especially in need of water during the first growth period, and root crops throughout the growth period, since interruptions in water supply cause root cracking. It should be taken into account that with an excess of moisture in the soil and the filling of pores with it, root respiration deteriorates, and plants die due to a lack of oxygen. In addition, the growth and development of beneficial soil microorganisms also deteriorate. At high soil moisture after planting transplants, their root system develops worse, which causes a decrease in the intake of nutrients by the plant, and as a result, the yield decreases.

When there is a lack of soil moisture, plant growth is primarily delayed, leaves develop poorly, less organic matter accumulates, the formation of the productive part of the plant is hindered, and, in the end, the harvest decreases. The lack of soil moisture not only affects the harvest of vegetables but also reduces their quality. This is especially true for moisture-demanding vegetables like radish (leaves become coarse, root crops lose juiciness and become more pungent in taste, plants grow rapidly, prematurely shooting flower-bearing shoots) and leafy greens. For the normal supply of water to plants, it is necessary to create a reserve of it in the root-inhabiting layer of the soil while simultaneously having air in the soil. This is only possible in structured soils; structured soils also ensure their good water permeability. The most important condition for obtaining an early and high harvest of vegetables is the uninterrupted supply of water and all necessary nutrients to the plants. However, this does not mean that vegetable plants need to be watered daily, and such crops as radish and leafy greens even twice a day, as inexperienced amateur vegetable growers do. What happens to the soil and plants during irrigation? After irrigation, the soil becomes compacted; with each subsequent irrigation, water penetrates to the roots of the plants worse and worse, and when the soil dries out, a soil crust forms. Capillaries form in the soil crust, through which water is pumped out of the soil and evaporates quickly, depriving plants of moisture. Moreover, in compacted soil, the amount of air decreases, the vital activity of beneficial microorganisms slows down, and the release of carbon dioxide, so necessary for plants, decreases. To eliminate all these disadvantages, it is necessary to perform loosening of the soil after every irrigation or rain. Loosening the soil destroys the capillaries, preventing the evaporation of moisture from the zone where the root system is located. Only the loosened top layer of soil dries out, while moisture is preserved underneath. Thanks to the influx of air, loosening improves the vital activity of microorganisms, which in turn enhances the release of carbon dioxide and improves the air nutrition of plants. However, the soil should be loosened only when it has "ripened," i.e., it does not smear, does not stick to the hoe or loosening claws, and crumbles easily; but one must not allow the soil to dry out to the point where it begins to dust during loosening — which means that much moisture has already been lost to evaporation. The next irrigation (even for radishes) should be carried out only the day after loosening on light soils, and on heavy ones — every other day, leafy crops and onions — every two to three days, cucumbers — every three to four days, cabbage — every five to seven days, and tomatoes — every 10–12 days. In the fruiting period, when plants require particularly high amounts of moisture, they should be watered more often. There is a general rule: on light soils, vegetables should be watered more often but with smaller application rates; on heavy soils — less often but abundantly, and in such a way that the water gradually soaks into the soil without forming puddles. If puddles form during irrigation, water stagnates and the wetting of the soil occurs only on the surface. To prevent this, hold the watering can closer to the ground and move quickly with it, returning to the same spot two or three times until the soil is fully soaked. If you have to use a hose, the water spray should be higher and misted so as not to damage the seedlings and not wash away the roots. It is better to water lettuce and tomatoes not by overhead irrigation, but along furrows made near the plants; otherwise, lettuce leaves rot easily, and tomatoes are more easily affected by late blight. After irrigation, when loosening the soil, the furrows should be covered with dry soil. For heat-demanding plants, the temperature of the irrigation water also matters: it should be no lower than the soil temperature, preferably 25°C; such water feels cool to the touch. It is better to water cucumbers and tomatoes with water heated by the sun, poured into a tub in the morning. During the hot hours of the day, cucumbers, as well as cauliflower, need to be sprayed with cold water using a hose, which helps increase the air humidity necessary for these plants and lowers the leaf temperature, protecting the plants from overheating. Spraying plants with water is especially necessary during the occurrence of a dry wind (a very dry hot wind), which also happens in the Non-Chernozem zone. A dry wind causes the drying and death of leaves, starting from the lower ones. In practice, so-called "drenching" of plants after frosts is often used. Such drenching with a small amount of water leads to the death of even hardened plants, as little heat is radiated from the unwetted soil, and the plants become covered with a crust of ice. The liquid moisture freezing on the surface of the leaves contributes to the formation of ice within the leaves themselves. A completely different picture is observed with abundant irrigation of the soil on the eve of frosts: moist soil releases heat, and the air temperature above the plants rises. Due to the increased air humidity above the irrigated plot, plants lose less heat through radiation, and when the air temperature drops, condensation of water vapor begins, resulting in the release of heat, which also delays the cooling of the plants. During frosts down to -3°C, plants should be sprayed every 10–15 minutes, in such a way that the soil is also moistened. The same irrigation should be carried out under the film on the eve of frosts. Then, fine-droplet moisture condensate forms on the film, protecting against the loss of heat rays. Spraying the film with water in the evening and covering it with a second layer of film also protects against heat loss, and plants — from frost. Air, or carbon, nutrition of plants. Carbon is the basis of organic matter. Carbon nutrition through the leaves, along with root nutrition with mineral substances, is of decisive importance when growing early vegetables and increasing their yield. After all, 45% of the plant's dry matter consists of carbon. Green parts of plants, using the energy of sunlight, absorb carbon from the carbon dioxide of the air, although the content of carbon dioxide in the air under normal conditions does not exceed 0.03%. An increase in the amount of carbon dioxide in the air layer near the ground is ensured by microorganisms that decompose the organic matter of the soil, and their development is increased due to the application of organic (manure, humus, compost) and mineral fertilizers, provided there is access to atmospheric oxygen. The more humus the soil has, the more carbon dioxide is released, and the better the carbon nutrition of the plants occurs. With the enrichment of plants with carbon dioxide, the growth and development of plants improve, the number of leaves increases and they are larger, fruiting accelerates, and the harvest increases. This is especially noticeable when growing vegetables in a protected environment, where the carbon dioxide content increases during the decomposition of manure laid for heating in hotbeds. With improved carbon nutrition, plants have increased resistance to diseases and pests. Even in open soil, to increase the concentration of carbon dioxide, in addition to applying fertilizers to the soil, plants are surrounded with fresh manure, but in such a way that it does not come into contact with the plants. The use of shelterbelts of tall crops protecting vegetable crops from the wind contributes to the preservation of carbon dioxide and moisture in the near-ground layer, which is especially important for cucumbers and cauliflower. Soil nutrition of plants. For the growth and development of vegetable plants, not only the quantity of necessary nutrients is of great importance, but also the correct ratio of nutritional elements. One-sided application, for example, of nitrogen fertilizers causes increased growth of vegetative organs and delays fruiting, and with a deficiency of other nutrients, plants develop poorly and produce a low harvest. The normal process of nutrient uptake by the root system can be disrupted by a lack of moisture and air in the soil (soil crust), by a decrease in temperature, and by the excessive application of mineral fertilizers. Individual vegetable plants differ sharply in their requirements for nutrients. For instance, radish and leafy vegetables, during a short growing season with high plant density, as well as transplants of vegetable crops, extract a large amount of nutrients, and during this period they must be provided with top dressing. An onion, over its four-month lifespan, extracts 2 times more nutrients than a radish does during a one-month growing season, and therefore also differs in increased requirements for fertilizers, but mainly for organic ones, as it cannot withstand a high concentration of the soil solution at the beginning of growth, just like carrots. Sources of nitrogen for plants, in addition to soil and organic fertilizers, are ammonium sulfate (contains 21% nitrogen), sodium and calcium nitrate (15–16% nitrogen), potassium nitrate (14% nitrogen and 47% potassium), and urea (46% nitrogen), which is especially effective on light soils under irrigation, where it quickly turns into ammonium carbonate and is easily absorbed by plants. Ammoniacal fertilizers are physiologically acidic; therefore, for neutralization, they should be mixed with lime or chalk, but to avoid loss of nitrogen, such mixing must be done immediately before the application of fertilizers to the soil. For 1 kg of ammonium sulfate, 1.2 kg of lime or chalk should be added; for 1 kg of urea — 0.8 kg. It is especially important to neutralize these fertilizers before applying them to sandy loam soils, as they acidify faster than other soils. With a nitrogen deficiency, plant leaves turn pale green, then yellow, and plants slow down their growth; while with an excess of nitrogen, they acquire a dark green color and grow vigorously, but flowering and fruiting are delayed. Unlike the natural death of lower leaves, where yellowing begins first between the leaf veins, when leaves die due to nitrogen deficiency, yellowing begins primarily from the leaf veins. In cabbage, along with yellow spots on the lower leaves, a crimson color appears, and head formation is delayed. In cauliflower, the formation of the head is delayed. In radishes, the leaf rosette develops poorly, as is the root crop. To ensure plant nutrition with phosphorus, phosphorus fertilizers are used: superphosphate (contains about 20% phosphorus). However, it should be taken into account that when using superphosphate on acidic soils in powder form, it turns into a poorly soluble form after some time, and phosphorus becomes inaccessible to plants. Therefore, it is better to apply phosphorus fertilizers in the form of granulated superphosphate (which contains up to 22% phosphorus) or precipitate (which contains 25–35% phosphorus), but the latter is insoluble in water; therefore, it is unsuitable for application in rows or holes, as well as for top dressing. For this purpose, superphosphate is used, in which the phosphoric acid is water-soluble and more accessible to young plants. It should be taken into account that in cold weather, plants absorb phosphorus poorly; at this time, top dressing of plants with phosphorus fertilizers is necessary. When applying superphosphate in a mixture with humus, the digestibility of phosphorus by plants increases, as under the influence of organic matter, a transformation of hard-to-reach phosphorus into an easily digestible form occurs. On acidic soils, especially on acidic peat soils, phosphorite flour is used (tricalcium phosphate — phosphorus

18%). However, it is better to use this fertilizer for preparing composts, in a mixture with powdered superphosphate. When applied in rows or holes, the efficiency of phosphorus fertilizers is higher than when they are broadcasted.

Young plants consume 2—4 times more phosphorus than older ones. Therefore, at-sowing application of these fertilizers is mandatory. Phosphorus fertilizers contribute to the improvement of root system growth, an increase in its branching, and a simultaneous increase in the number of root hairs.

When there is a lack of phosphorus, plant growth slows down, and fruit ripening is delayed. A lack of phosphorus for just a few days after emergence adversely affects the entire subsequent development of the plants and leads to a decrease in yield; furthermore, subsequent application of phosphorus fertilizers cannot eliminate this decrease.

Symptoms of phosphorus deficiency in various crops:

• In tomato seedlings: violet-red coloring of the underside of cotyledonary leaves, cotyledons directed upwards at an acute angle, true leaves also take on a purple or violet-red coloring on the lower surface.
• In adult plants: lower leaves dry out at the edges, the dried areas quickly turn black and crumble.
• In cabbage: leaves grow poorly and small heads are formed.

Phosphorus is necessary for tomatoes, as well as cucumbers, from the moment of seed germination. A lack of phosphorus at this time is not compensated by subsequent top dressing with phosphorus fertilizers. The application of phosphorus fertilizers during the sowing of root crops and planting of potatoes contributes to strengthening the root system and accelerates the formation of root crops and potato tubers by seven to ten days.

Annual application of high doses of superphosphate to the soil leads to soil over-phosphating, and with an excess of phosphorus, a lack of iron is detected in plants, since phosphorus converts iron into forms inaccessible to plants. Therefore, in old vegetable gardens, before applying phosphorus and other fertilizers, the soil should be sent for analysis to the nearest agrochemical laboratory.

A lack of potassium is most often observed on sandy soils, from where it is easily leached, but a minimal amount of potassium is contained in floodplain and peat soils. Signs of potassium deficiency in plants are browning of leaf edges as if from a burn; they curl up and are affected by brown spot, and plants are easily affected by fungal diseases.

Features of potassium deficiency manifestation:

• In tomatoes: lower leaves turn yellow between the veins, the leaf flesh becomes convex and wrinkled, and greenish-yellow spots appear on the fruit.
• In cucumbers and beets: leaves take on a dome-like shape, mainly male flowers develop on the plants, and fruits become pear-shaped.

Among potassium fertilizers, potassium chloride and potassium salts are most often used, but these fertilizers contain a lot of chlorine. Chlorine is necessary for plants, but its excess is harmful to cucumbers, tomatoes, and potatoes. With an excess of chlorine in the soil, vegetable yields are often lower, the sugar content of tomato fruits decreases, the starch content of potato tubers decreases, and their taste deteriorates.

The application of potassium salts for beets contributes to an increase in yield and an increase in the sugar content of root crops. The excess of chlorine in these fertilizers does not affect the yield of beets. In experiments at the Lyubertsy experimental field of the Moscow Region on sandy soils, the yield increase of sugar beets from the application of potassium chloride averaged 35% over nine years, and from potassium salt — 52%.

Potassium chloride and potassium salts can be used not only for beets, but also for spinach, Swiss chard, and carrots. For cucumbers, tomatoes, and potatoes, it is better to use potassium sulfate, and on sandy soils, where magnesium is also often lacking, potassium-magnesium sulfate or potassium-magnesium should be used. Potassium nitrate is a valuable fertilizer for top dressing cucumbers and tomatoes during the fruiting period.

For the fertilization of vegetable, floral, and fruit-berry crops, compound fertilizers are produced, containing 6—6.4% nitrogen, 9.6—9.8% phosphorus, and 6.4—9% potassium (less in the flower mixture, more in the garden mixture). These mixtures are prepared from ammonium sulfate, superphosphate, and potassium chloride. In addition, nitroammophoska and nitrophoska are produced: the content of nitrogen, phosphorus, and potassium in them averages 17% each.

Ammonium sulfate is simultaneously a sulfur fertilizer (24% sulfur), just like superphosphate (12% sulfur) and potassium sulfate. Sulfur is necessary for cabbage, radish, as well as onions and garlic. The application of magnesium fertilizers on soils where there is not enough magnesium significantly increases the sugar content in beet root crops, in the fruits of tomatoes, watermelon, and pumpkin, and increases the starch content of potato tubers. With a lack of magnesium, the color of the leaf tissue between the veins changes to yellow, red, or purple. In tomatoes, brown spots appear between the green veins, and in cucumbers, the edges of the leaves turn brown.

Sometimes a magnesium deficiency manifests as signs of phosphorus deficiency. This is explained by the fact that in plants, magnesium deficiency hinders phosphorus absorption. Magnesium starvation intensifies with an increase in soil acidity. It should be noted that when manure is applied to the soil, magnesium fertilizer application may not be necessary, as in this case, plants are fully provided with the magnesium contained in the manure.

Vegetable crops react differently to the calcium content in the soil. This element directly affects the growth of the plant root system. On acidic soils, without preliminary liming, it will be impossible to grow crops that are demanding of calcium — you will simply lose the harvest.

Calcium nutrition of vegetable crops and liming

Beet, onions, cucumbers, and legumes are particularly sensitive to calcium deficiency. By liming acidic soils for these crops, you significantly increase the efficiency of applied mineral fertilizers. As a result of nutrient optimization, the following changes occur:

• the content of ascorbic acid and carotene in vegetables increases significantly;
• the availability of phosphorus and magnesium for plants increases;
• the physical properties and structure of the soil improve;
• the vital activity of beneficial soil microorganisms is enhanced;
• disturbances in protein metabolism and sugar formation in plants are eliminated;
• the development of harmful fungi is prevented.

To calculate lime doses, it is necessary to first determine the soil acidity. This can be done at the nearest agrochemical laboratory or approximately by the vegetation directly in the field. Characteristic weeds will help you quickly orient yourself on-site.

On neutral soils, the following grow well:

• clover;
• orache;
• nettle.

On acidic soils, the following develop:

• field horsetail;
• sorrel.