Hydroponics, a soilless method of cultivating plants, has seen a surge in popularity in recent years due to its numerous advantages over traditional soil-based farming. These benefits include more efficient water usage, faster plant growth, and the ability to grow crops in confined spaces. However, for hydroponic systems to perform at their best, several critical factors must be carefully managed. Among these, dissolved oxygen plays a pivotal role.

In a hydroponic system, plants grow in a nutrient-rich water solution. Unlike soil, which naturally contains air pockets to supply oxygen to plant roots, hydroponic systems depend on the dissolved oxygen in the water to fulfill the oxygen requirements of the roots. The availability of adequate dissolved oxygen can significantly influence the health, growth, and productivity of hydroponic plants. This blog explores the concept of dissolved oxygen, its essential role in hydroponics, why it is so vital, the optimal levels required, and effective methods to monitor and measure it.

What is Dissolved Oxygen?

Dissolved oxygen (DO) is the measure of oxygen gas (O₂) present in a liquid, usually water. It enters the water through gas exchange at the interface between air and water. Furthermore, photosynthetic organisms like algae and certain aquatic plants contribute oxygen to the water during photosynthesis.

Physical and chemical factors affecting dissolved oxygen

Temperature: The solubility of oxygen in water is inversely proportional to temperature. As the temperature of water increases, the solubility of oxygen decreases. For example, cold water can hold more dissolved oxygen than warm water. At 0°C, water can hold approximately 14.6 mg/L of dissolved oxygen, while at 20°C, the solubility drops to about 9.2 mg/L.

Salinity: Higher salinity levels in water also reduce the solubility of oxygen. Seawater, which has a higher salt content than freshwater, can hold less dissolved oxygen at the same temperature and pressure.

Atmospheric pressure: Dissolved oxygen levels are directly related to atmospheric pressure. At higher altitudes, where the atmospheric pressure is lower, the amount of oxygen available to dissolve in water is also reduced.

Natural sources of dissolved oxygen

Atmospheric diffusion: Oxygen from the air continuously diffuses into the surface of water bodies. This process is enhanced by factors such as wind, waves, and water movement, which increase the surface area of water exposed to the air.

Photosynthesis: Aquatic plants and algae produce oxygen as a by - product of photosynthesis. During the day, when there is sufficient light, these organisms can significantly increase the dissolved oxygen levels in the water.

Dissolved Oxygen in Hydroponics

How plants obtain oxygen in hydroponics?

In a hydroponic system, plant roots are directly exposed to the nutrient solution. The roots need oxygen for respiration, a process by which they convert stored energy (in the form of carbohydrates) into usable energy (ATP). Without an adequate supply of oxygen, the roots cannot carry out this essential metabolic process efficiently.

In a well - oxygenated hydroponic solution, oxygen molecules are available for the root cells to absorb. The root cells have specialized structures called root hairs, which increase the surface area for the absorption of oxygen and nutrients. As the roots take in oxygen, they release carbon dioxide into the solution.

Different hydroponic systems and their impact on dissolved oxygen

Deep Water Culture (DWC): In a DWC system, plants are suspended in a nutrient solution with their roots fully submerged. Air stones or diffusers are commonly used to introduce bubbles of air into the solution. These bubbles increase the surface area of the water - air interface, promoting the diffusion of oxygen into the water. However, if the water temperature is too high or the air supply is insufficient, the dissolved oxygen levels in a DWC system can quickly drop.

Nutrient Film Technique (NFT): NFT systems involve a thin film of nutrient solution flowing over the roots of the plants. The constant flow of the solution helps to keep the roots oxygenated. As the solution moves along the channels, it comes into contact with the air, allowing for oxygen exchange. Additionally, the thin film of water ensures that the roots are not completely submerged, reducing the risk of oxygen depletion.

Ebb and Flow (Flood and Drain): In an ebb and flow system, the nutrient solution periodically floods the growing tray and then drains away. During the flood phase, the roots are submerged in the nutrient solution, and during the drain phase, they are exposed to air. This alternating cycle helps to provide oxygen to the roots. However, if the flood and drain intervals are not properly adjusted, the roots may not receive enough oxygen.

picture from https://hgshydro.com/

Why is dissolved oxygen so important in hydroponics?

Root health and development

Aerobic respiration: As mentioned earlier, plant roots require oxygen for aerobic respiration. Aerobic respiration is a more efficient process compared to anaerobic respiration, which occurs in the absence of oxygen. In aerobic respiration, glucose is completely broken down into carbon dioxide and water, releasing a large amount of energy in the form of ATP. This energy is used for various cellular processes, including root growth, nutrient uptake, and the synthesis of essential compounds.

Root growth and branching: Adequate dissolved oxygen promotes healthy root growth and branching. When roots have access to sufficient oxygen, they can grow longer and develop more lateral roots. This increased root surface area allows the plants to absorb more nutrients and water from the hydroponic solution, leading to better overall plant growth.

Resistance to diseases: Well - oxygenated roots are more resistant to diseases and pathogens. Oxygen helps to maintain the integrity of the root cell walls, making it more difficult for harmful organisms to penetrate and infect the roots. Additionally, a healthy root system can produce antimicrobial compounds that help to protect the plant from diseases.

Nutrient uptake

Ion transport: Nutrient uptake by plant roots is an active process that requires energy. The energy produced through aerobic respiration is used to power the ion transporters in the root cells. These transporters move nutrients such as nitrogen, phosphorus, and potassium from the hydroponic solution into the root cells against a concentration gradient. Without sufficient oxygen, the root cells cannot generate enough energy for efficient nutrient uptake, leading to nutrient deficiencies in the plants.

Nutrient solubility: Dissolved oxygen can also affect the solubility of certain nutrients in the hydroponic solution. For example, some metals such as iron and manganese are more soluble in an oxygenated environment. This means that plants are more likely to be able to absorb these nutrients when the dissolved oxygen levels in the solution are adequate.

Microbial activity

Beneficial microorganisms: Hydroponic systems are home to a variety of microorganisms, some of which are beneficial to plant growth. These beneficial microorganisms, such as certain bacteria and fungi, play important roles in nutrient cycling and disease suppression. Many of these microorganisms are aerobic, meaning they require oxygen to survive and function. Adequate dissolved oxygen levels in the hydroponic solution support the growth and activity of these beneficial microorganisms, which in turn can enhance plant health.

Prevention of harmful anaerobic bacteria: In the absence of sufficient oxygen, anaerobic bacteria can thrive in the hydroponic solution. These bacteria can produce harmful by - products such as hydrogen sulfide, which has a foul smell and can be toxic to plants. By maintaining high dissolved oxygen levels, the growth of anaerobic bacteria can be suppressed, reducing the risk of plant damage.

What is the ideal dissolved oxygen level for hydroponics?

General guidelines

The ideal dissolved oxygen level for hydroponics can vary depending on several factors, including the type of plants being grown, the hydroponic system used, and the water temperature. However, as a general rule, a dissolved oxygen level of 5 - 8 mg/L is considered optimal for most hydroponic crops.

Factors influencing the ideal level

Plant species: Different plant species have different oxygen requirements. For example, some plants such as lettuce and spinach are relatively tolerant of lower dissolved oxygen levels, while others such as strawberries and tomatoes require higher levels. Plants with larger root systems or those that grow more vigorously generally need more oxygen.

Growth stage: The oxygen requirements of plants can also change during different growth stages. Young plants may have lower oxygen requirements compared to mature plants. During the flowering and fruiting stages, plants often require more oxygen to support the development of flowers and fruits.

Water temperature: As mentioned earlier, the solubility of oxygen in water decreases with increasing temperature. Therefore, in warmer water, higher levels of aeration may be required to maintain the ideal dissolved oxygen levels. For example, in a hydroponic system operating at 25°C, it may be necessary to maintain a dissolved oxygen level closer to 6 - 8 mg/L, while at 15°C, a level of 5 - 7 mg/L may be sufficient.

How to measure dissolved oxygen for hydroponics?

Dissolved oxygen meters provide a highly accurate and dependable method for assessing dissolved oxygen levels in hydroponic solutions. These devices usually feature a probe equipped with a sensor that detects the partial pressure of oxygen in the solution and translates it into a dissolved oxygen concentration reading.

Y600-A&Y507-A Portable Dissolved Oxygen Meter-Water Quality Sensor Manufacturer-Yosemitech (yosemitesensors.com)

Conclusion

Dissolved oxygen is crucial for hydroponic success, impacting root health, nutrient uptake, and microbial activity. Maintaining optimal levels ensures healthy plant growth and productivity.

As hydroponics evolves, advancements in oxygen management will improve efficiency. Growers should stay updated on innovations and adopt best practices to maximize system potential. Yosemitech provides different kinds of dissolved oxygen sensors & meters for measuring dissolved oxygen, if you want to purchase do sensor, feel free to contact us!