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Ben Peters
Technical Accountmanager | August 22, 2024 | 5 min. reading time

• The importance of oxyen in the root environment
• Causes of oxygen shortage
• Consequences of oxygen shortage

For the respiration of plant cells, it is important that there is sufficient oxygen present. The proportions of water and air in the soil or substrate is largely determining for the oxygen quantity. The air contains 21% oxygen. In water, oxygen values are measured up to around 12 milligram per liter. This dissolved oxygen value is of major importance, because the respiration of cells takes place in the plasma.

Also measurements show that the oxygen content has a visible effect on the development of the plant. This applies to foliage growth as well as the development of the roots. The following images clearly show this effect:

​​​​Influence of oxygen on cucumber growth​​​​

​​​​Influence of oxygen on the growth of lettuce​​​​

Organic pollution or the emergence of a biofilm in a drip irrigation system could cause reduction of oxygen contents. When the water is stagnant, the oxygen in it is consumed by, for example, bacteria and the oxygen content will drop to critical values (<4 mg/l) within an hour. For that reason, regular purification and cleaning of piping is an important measure to safeguard against oxygen shortage. Apart from this, a continuously wet mat could contribute to an oxygen shortage. Roots will in that case not have the opportunity to optimally take up oxygen or the available nutrients. Also practice tests have demonstrated that oxygen shortage near the roots can be attributed to high temperatures in the substrate mat. This high mat temperature and a too wet mat are ideal growth conditions for bacteria and fungi (Pythium in particular), making them reproduce easily.

Oxygen, assimilates, water and CO2 ensure the formation of ‘energy-rich connections’. These connections are imperative for the uptake of nutrients, among others and to keep cells under tension. Additionally, it ensures that sodium is being kept outside the roots. 

In case of a shortage of oxygen in the root environment fewer energy-rich connections can be formed. This will have all kinds of negative consequences. For example, root growth will be strongly diminished, or will even come to a full stop. Also the uptake of nutrients will be strongly reduced, which may lead to deficiency symptoms. In practice, in case of oxygen shortage, often higher nitrite values are measured. This is because nitrate (NO3) is converted to nitrite (NO2) in case of a lack of oxygen (O). Too high nitrite values are toxic for both humans and plants.

Especially in the summer, oxygen shortage is a major. Due to the high temperature, the oxygen content could drop below 4mg (or 10%) in a very short period of time. When this happens, it will cause problems/stress for the plant.

Since the oxygen content is influenced by multiple factors (for example irrigation strategy, climate control and temperature) and is therefore hard to predict, it is important to adequately monitor the content. There has always been attention for oxygen, but until recently it was not possible for growers to measure it in a proper and reliable way. Nowadays there is in fact a solution available. Applying new technology, sensors have been developed that you can use yourself to both determine and monitor the oxygen content in the substrate. These sensors gather data that can subsequently be compared, via a platform, with other cultivation factors to ultimately assess the relationships. This may lead to new insights in the area of climate control, irrigation and plant resilience.

Moleaer is a gas injection technique that dissolves oxygen into water with extremely high efficiency, achieving up to 85%. In contrast, conventional techniques only reach 20%. As a result, conventional methods often show significant bubbling, which indicates loss. Moleaer can inject nearly 1 billion bubbles per milliliter of water, each approximately 100 nm in size. This is 2,500 times smaller than a grain of salt. 

There are two different types of Moleaer systems. The 'Clear' type is used to combat contamination and algae growth in water storage (such as reservoirs). The 'Neo' type is installed on, for example, a clean water silo or daily storage silo, treating the water shortly before it is directed toward the crops. This results in higher levels of dissolved oxygen in the water, regardless of whether the water is cold or warm. In addition to a more efficient uptake of nutrients, Moleaer also helps keep water pipes cleaner. This is not primarily due to the oxygen but because the system imparts a negative surface tension to the water. A lower surface tension makes it easier for dirt to be removed by the water. Moreover, growers are able to use fewer fungicidal crop protection agents, as experience shows that diseases such as Fusarium or Pythium can be significantly reduced. For water reservoirs, chemical corrections with sulfuric acid or agents based on active copper are rarely, if ever, necessary. 

​​​​Pepper grower Rob Moors – Moors Nursery​​​​

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