Moulton College lecturer warns on Iceland volcano effect on horticulture

Moulton College senior horticulture lecturer Dr Russell Sharp has warned that sulphur from the Icelandic volcano eruptions that is halting UK plane flights has a number of significant effects on plant growth.

Sharp, who is also college research coordinator, said: "Sulphur is a plant macronutrient that is needed in fairly large amounts for the synthesis of chlorophyll and amino acids.  A significant amount of sulphur was historically added to British soils due to industrial pollution, but due to the clean air laws this has been reduced of late.

"This current plume of ash and gas may represent a needed increase in soil sulphur levels if it makes it down to the ground dissolved in rain, and reduce the need to add sulphur through synthetic fertilisers.

"However, sulphur is not always wanted when growing certain plants. Sulphur is a component in the bitter chemical compounds produced in onions and its relatives. Increased sulphur loads in the soil may increase the bite of Allium crops. Sweet Onions are grown in Georgia in the USA specifically because the soil there is low in sulphur. Sulphur can also be directly toxic to all plants in high amounts by disrupting the uptake of other nutrients and leading to premature leaf drop, but this would require a massive increase in levels beyond that currently in most soils.

"Sulphur dioxide (SO2) is one of the most important sulphur-containing atmospheric pollutants from industrial pollution as well as volcano eruptions. It has antifungal properties and sulphur is commonly used as a fungicide in horticulture, including organic production. 

One of the major benefits of increased atmospheric sulphur levels as a result of the ash cloud could be that it may kill or harm plant pathogenic fungi and water moulds. Would it not be great if it could wipe out the likes of Honey Fungus, Sudden Oak Death, Damping Off Disease, Mildews or Grey Mould!  However, in high concentrations, sulphur would also have a detrimental effect on symbiotic mycorrhizae fungi. 

Therefore, growers may need to "seed" their plants with mycorrhizae spore preparations to replace those lost to the plume. Mycorrhizae are particularly important for growers of conifers and orchids. Without these fungi symbionts the plants may have depleted nutrition (especially phosphorus), reduced water uptake capacity, and increased risk of infection; as mycorrhizal fungi help the plant with all these processes. Growers do not normally need to seed their growing media with mycorrhizae because the spores are already present in the soil and on the plant, however, they can be useful when the plant has lost an association due to the fungi dieing, such as when fungicides are used to kill off a pathogenic fungal infection on the same plant or nearby.  

"Sulphur is a key component of acid rain, although the effects of acid rain are normally seen on a long time scale.

"Clearly we do not know the extent of severity of the current volcanic activity, however, I would advice growers of crops that rely on mycorrhizae fungi is to keep an eye on their crops, monitor developments closely and consider purchasing preparations of mycorrhizae spores to re-seed their growing media."


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