Oxygen is not a critical factor because there is plenty of it in the air. During the day, when the plants are photosynthesizing, they actually release oxygen as a byproduct of sugar production. No additional oxygen is needed above ground.
The roots use oxygen and absorb it directly from the soil or from water that contains dissolved oxygen. The amount of dissolved oxygen water can hold is determined for the most part by its temperature. The cooler the water, the more oxygen it holds. This is one of the main reasons for root deterioration when it occurs in hydroponics systems. Warm water doesn’t hold much oxygen. This anaerobic condition sets the stage for pathogens to attack the stressed roots. There are several ways to add oxygen to your water:
? Keep the soil or hydroponic irrigation water at about 72?F (22?C). At this temperature the water has the ability to hold sufficient oxygen. If the water temperature gets higher, use a water chiller, available from aquarium fish supply stores. These units keep the water in the reservoir cool even when the surrounding temperature is quite high. This can save plants even when the air temperature reaches 90?F (32?C). The cool roots, with access to plenty of oxygen, keep the plant healthy and mitigates the damage that hot air would normally cause.
? Use an air pump to keep the water circulating using the venturi effect, or even better, use a small submersible pump to create a mini waterfall. This turbulence helps the water make contact with air. During this contact the water exchanges the carbon dioxide it is holding for oxygen.
? When the water temperature rises above 75?F (24?C), the amount of oxygen it can hold diminishes dramatically. For that reason, the water should be kept between 69-72?F (20-22?C). If the air temperature is on the high side, the water can be kept even a few degrees cooler.
? A loose soil, that provides spaces to hold air as well as water, usually provides sufficient oxygen exchange for roots.
? Oxygen can be supplemented using hydrogen peroxide (H2O2) at the rate of about one part per 500 in the water nutrient solution. If using 10% H2O2, often sold in indoor garden shops, dilute it 1 part in 50. If using pharmacy grade 3% H2O2, dilute at the rate of one part H2O2 to seven parts water, or about a pint per gallon.
? Hydroponic water can be enriched with hydrogen peroxide at the same rate as irrigation water. H2O2 is used to kill pathogens and algae in hydroponic systems at the rate of about 1 part per 100 or about 13 ounces of 10% H2O2 or 40 ounces of 3% per gallon. However at the rate of 1 part in 500, or .2%, it will still benefit the soil but it will have little effect on microbial life.
Hydrogen peroxide, H2O2 is water that is charged with an additional oxygen (O) atom. This atom has a tendency to jump from its unstable bond and combine with some other molecule. That is why hydrogen peroxide can burn skin and clothing. Since it is an unstable molecule, the O may jump off the H2O2 and combine with another O atom to form a molecule of 2 O atoms, O2. The H2O that remains of the molecule is water. The O2 molecule remains dissolved in the water. It is ready to be picked up by an oxygen-hungry root.
The hydrogen peroxide seems to remain effective for about three days. Then more is added.
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