The influence of atmospheric air composition on the productivity of vegetable crops

The composition of atmospheric air changes depending on the geographical location of regions and their saturation with industrial enterprises, transport, and modern technical equipment that emit polluting substances. However, the content of molecular nitrogen (78%), oxygen (21%), and carbon dioxide (0.03%) is practically the same everywhere. The air also contains various toxicants—the result of human activity and natural emissions (volcanoes, geysers). Among them, the greatest danger to plants is posed by sulfur dioxide, fluorine compounds, hydrogen chloride, nitrogen oxides, photochemical oxidants, and dust particles containing adsorbed gases and oxides of various substances, including heavy metals. At excessive concentrations, carbon monoxide, ozone, ammonia, ethylene, methane, chlorine, and others also have a depressing effect on plants. Atmospheric pollution occurs mainly due to emissions from motor vehicles (60%) and industrial enterprises.

Of the air components, carbon dioxide and oxygen are of the greatest importance for plants. The former is the main source of carbon input into plants through photosynthesis, while the latter is necessary for their respiration. In addition, oxygen is actively used by soil microorganisms, which are closely linked to the life of plants.

It has been experimentally established and confirmed by practice that increasing the carbon dioxide concentration in the air to 0.2-0.3% (and in some experiments with cucumber plants, up to 0.6%) significantly increases the photosynthetic activity of plants, which positively affects their yield (by 20-30%). A decrease in the content of this gas to 0.01% leads to the suspension of photosynthesis, while an increase to 1% can have a depressing effect on the plant.

Vegetable plants on an area of 1 hectare daily absorb more than 500 kg of carbon dioxide; for this, almost 1 million m3 of air must pass through them. Its replenishment occurs primarily due to the active decomposition of organic matter by microorganisms in the soil. In addition, this gas is released during the respiration of living organisms, when burning fuel, and during the operation of industrial enterprises. The richer the soil is in organic substances, the more carbon dioxide reaches the growing plants. Sufficiently fertile soils, with good aeration, release 300-550 kg of CO2 per 1 hectare per day. Unfertilized sandy soil releases 5-12 times less CO2. The looseness of the soil, which determines the exchange between soil and atmospheric air, has a significant effect on the activity of organic matter decomposition in the soil. Soil compaction prevents such exchange and leads to supersaturation with carbon dioxide in areas adjacent to plant roots.

The oxygen content in the air is sufficient for active plant metabolism. Even a slight decrease in its amount stimulates photosynthetic productivity, while a concentration above 21%, on the contrary, inhibits photosynthesis (to a small extent). Most often, a lack of oxygen is felt in the soil during waterlogging and severe compaction, which prevents water uptake by roots and, as a result, leads to a delay in growth processes.

Vegetable plants react noticeably to changes in the concentration in the air of ethylene, released by the fruits of melon, tomato, pepper, eggplant, pumpkin, watermelon, and others. With its low content (0.04-10 µl/l), root formation and the germination of bulbs, seeds, and pollen are stimulated in some plants.

In cucurbits (cucumber, pumpkin, melon), ethylene stimulates the formation of female flowers. The use of ethephon, hydrel, and camposan preparations in hybrid seed production is based on this.

In natural conditions, the negative impact of ethylene on vegetables is often manifested. Storage of ethylene-releasing fruits (tomato, melon, pumpkin, pepper, etc.) together with other vegetables leads, for example, to premature yellowing and spoilage of cucumbers and leafy greens.

It is worth noting one more gas that vegetable growers often encounter, especially those working in greenhouses—ammonia. It is released in large quantities during the decomposition of manure and some other substances of organic origin.

Consequences of the impact of ammonia on plants:

• At a concentration of 0.1-0.6%, plant depression is observed.
• With an increase in concentration to 4%, plant death occurs within a day.

This gas is accompanied by methane, which is also released during the decomposition of some organic fertilizers and affects plants in a manner similar to ammonia. Substances that pollute atmospheric air, even in small concentrations, block photosynthesis and inhibit the growth and development of plants, and with their high content and prolonged exposure, plant death is observed.

The task of an agronomist is to create a favorable air-gas regime in both natural conditions and greenhouse environments, ensuring high photosynthetic productivity and maximum accumulation of vegetable harvest. An increase in carbon dioxide content is usually achieved by enriching the soil with organic substances and creating conditions for their active decomposition with the help of microorganisms. For optimal aeration and humidity, loosening and irrigation are necessary. The application of 30 tons of manure per 1 hectare provides an additional 100-200 kg of carbon dioxide per 1 hectare per day.

In modern low-volume greenhouses top dressing of plants with carbon dioxide is a mandatory element of intensive technology. Without artificial saturation of the air, plants cannot fully reach their potential. The practice of leading greenhouse complexes shows that increasing the CO2 concentration to 0.2–3.0% increases the yield of cucumber by 21–27%, and of tomato by 27–32%. At the same time, optimal gas doses depend directly on light intensity, and the supply regime depends on the airtightness of the greenhouse and leaf area.

• Increase in cucumber yield — 21–27%
• Increase in tomato yield — 27–32%
• Single application rate — 10–15 g/m³

For effective saturation of the air with carbon dioxide, it is important to strictly observe the technological regulations. Flue gases from boiler plants, natural gas, or solid carbon dioxide are used as sources of CO2. Gas must be applied according to rules that take into account the time of day and the plant development phase.

1. Calculate the dosage based on the volume of the greenhouse structure (10–15 g of carbon dioxide per 1 m³).
2. Supply the gas during morning hours with closed vents.
3. Ventilate the greenhouse no earlier than 2 hours after CO2 application.

Growing clean produce in open soil

Unlike protected soil, where the microclimate is fully controlled, in field conditions the overall environmental safety of the area comes to the fore. To guarantee the production of clean vegetables, it is necessary to exclude areas with a risk of air contamination by toxicants from the crop rotation. When planning planting, be sure to consider the location of roads and factories.

• Do not place vegetable fields closer than 500 meters to highways.
• Do not grow vegetables in areas located downwind from industrial centers.