Application of carbon fertilizers to increase crop yield

The primary building element for plants is carbon. During photosynthesis, they assimilate it in the form of carbon dioxide (CO2). Crops absorb the majority of this gas from atmospheric air; however, the root system also actively absorbs dissolved carbon dioxide from the soil.

The ratio of carbon nutrition sources is distributed as follows:

On average, atmospheric air contains about 0.3 cm³/l of carbon dioxide, while its concentration in soil air reaches 3 cm³/l. Approximately 8,000 m³/ha of carbon dioxide is released from the soil into the atmosphere annually. Above fields where organic and mineral fertilizers are applied, the carbon dioxide concentration is higher, ranging between 0.28–0.61 mg/l.

In greenhouse conditions, especially when growing crops hydroponically, a deficiency of carbon dioxide occurs during daytime hours in the spring and summer (its normal content in the air is only 0.03 %). A shortage of CO2 sharply reduces the intensity of photosynthesis and leads to yield losses. Therefore, in greenhouses, plants require additional artificial carbon supply during the daytime.

Methods of applying carbon fertilizers

To compensate for carbon deficiency, several types of fertilizers are used in practice:

• gaseous carbon dioxide;
• solid carbon dioxide (dry ice);
• products of catalytic (flameless) combustion of gas and solid fuel;
• mineral carbonate salts and organic fertilizers.

Gaseous carbon dioxide is supplied from cylinders into greenhouses during the day. When top dressing cucumbers in greenhouses, the yield increases by 25–74 %. In tomatoes, carbon enrichment causes the bush to grow actively, but the fruit harvest increases insignificantly, although ripening is accelerated and product quality improves. In open fields, gaseous carbon dioxide is supplied along with irrigation water during sprinkling, which increases the sugar beet harvest and raises the sugar content in the root crops.

• Yield increase of cucumbers in greenhouses — 25–74 %
• Yield increase of sugar beet — 20–25 %
• Increase in beet sugar content — 0.5–1.0 %
• CO2 content in catalytic combustion gas — up to 15 %

Solid carbon dioxide (dry ice) is used for greenhouse gasification according to the following scheme:

1. Calculate the required volume of dry ice based on the cubic capacity of the greenhouse.
2. Crush the solid carbon dioxide blocks into pieces weighing about 0.5 kg.
3. Evenly distribute the resulting pieces on racks throughout the greenhouse for evaporation.

To obtain carbon dioxide directly on-site, special flameless combustion furnaces are used. When burning domestic gas or solid fuel, a mixture containing up to 15 % CO2 is formed, which is introduced into the greenhouse to gasify the plants.

Mineral carbonate salts and organic fertilizers also serve as a source of CO2. During mineralization in the soil, organic matter releases carbon dioxide, which is assimilated by leaves and roots. The intensity of CO2 emission depends on the volume of applied organic matter and the amount of plant residues. Additionally, in open and closed soil, carbonate salts of potassium, sodium, and ammonium can be used.