As featured in Arable Farming Magazine
Reducing crop stress with silicon
by Arable Farming Magazine April issue
Silicon rarely gets a second thought in crop nutrition. Might that be about to change?
It is the Earth’s second-most abundant element and makes up about half the content of any typical soil type, so crop nutrition strategy hasn’t prioritised silicon.
Dr David Marks, crop scientist and founder of Levity Crop Science, says: “Silicon has never enjoyed ‘essential nutrient’ status.
“Conventional thinking has it that crops can absorb sufficient quantities from soil.
“Because we give it so little attention, silicon’s role in plant metabolism and structural integrity is barely acknowledged.”
Dr Marks adds that crop scientists think silicon needs to gain greater prominence in crop nutrition.
More and more research suggests it could deliver further yield potential from a range of crops, cereals included, he says.
Silicon is implicated in several metabolic functions, including the production of stress-protecting hormones, antioxidants and biotic stress protectors.
“Its ability to confer stress tolerance, whether abiotic – environmental factors such as drought and high temperatures – or ‘biotic’ stress caused by pests and diseases, is interesting,” he adds.
Experience “We don’t know how climate change will affect agriculture, but it’s generally accepted that crops will experience stress events more frequently.”
Silicon is instrumental in the redistribution of phosphate through the plant, and for efficient transport of the trace elements zinc, manganese, iron and copper.
It also improves crops’ nitrogen recovery, particularly in cases of low N availability.
Lastly, plants also use silicon to create a hard crystal layer within the cuticle.
These insoluble deposits, called ‘opals’ – not dissimilar to the small packets of silica gel used as desiccants – lend physical strength to the plant structure.
Opals offer strong defence against attacks from pests and diseases.
“They slow the speed of colonisation of fungal pathogens, stopping them from penetrating JLevity believes silicon could benefit a range of crops, with further trials underway in: Cereals: Improved resistance to lodging; better stress resistance Onions: Improved drought resistance Potatoes: Reduced incidence of aphid feeding (owing to tougher cuticles), improved skin and tuber quality, less susceptibility to cold stress Silicon in trials more than a couple of cells deep into the leaf.
They also improve structural robustness, increasing stem thickness and reducing the plant’s susceptibility to lodging,” says Dr Marks.
Establishing the need for silicon is one thing, he says, but there are three problems with satisfying that need.
“Once silicon is deposited as opals, the plant enjoys physical protection but the silicon is no longer metabolically active; it cannot be released,” says Dr Marks.
“Secondly, much of the soil silicon is not bioavailable, as silicic acid [H4SiO4].
“Lastly, in common with other soil nutrients, plants face competition from bacteria and diatoms for any bioavailable silicon.”
In seeking to address these problems, attempts have been made to apply silicon through foliar applications.
As Dr Marks explains, scientists faced another barrier.
“Silicon isn’t mobile in the phloem, which means the plant has to actively transport it into and out of the xylem to move it around the plant.
It’s a metabolic process, limiting transport and mobility,” he adds.
“The challenge is to mobilise it before it’s locked away as opals.
While it’s great to have the additional physical protection, we need the metabolic benefits too.
“The only way to achieve this is through regular applications during the growing season, supplying silicon little and often.
“That’s acceptable in a research setting, but at that frequency and volume it’s commercially impractical.”
So, about 12 years ago, Dr Marks began to examine an alternative approach.
Research revealed that while all crops use silicon, different species exhibited varying abilities to accumulate it.
This was a key observation: as silicon moves only in the xylem, the expectation would be that silicon should accumulate at a rate commensurate with transpiration.
“Yet some plants, like rice and sugarcane, take up silicon at a higher rate than present in the transpiration stream,” says Dr Marks.
“Rice can contain as much as 15%.
This has to occur using active transport.
“Meanwhile, there are very low accumulators – most dicot plants, for example – that can’t even absorb the silicon in soil solution.”
Armed with these findings, Dr Marks embarked on a project to not only identify the substances responsible for silicon transport, but to emulate them.
This approach, he says, is the hallmark of Levity’s nutritional portfolio.
He says: “We try to create ‘smart’ fertilisers: substances that stimulate or ‘supercharge’ the plant’s own metabolic pathways.
We’re helping the crop to help itself”
Inactive Previous research successes include LoCal, a calcium transport stimulant that improves the quality and shelf-life of fruit crops and a boron product, Damu, which helps the plant regulate carbohydrate transport.
He adds: “To tackle silicon, we created Si-X technology.
This stimulates naturally-occurring silicon transporters within the plant, avoiding the problems of conventional foliar silicon becoming metabolically inactive once it’s crystallised.”
Now patent-pending, Si-X has been formulated into Levity’s Zeme.
It saw its first major field trials in 2020.
Two one litre per hectare applications were made in spring wheat at T1 and T2, tank-mixed with conventional fungicides.
The trial was conduct ed during a dry spring period, with the crop identified as in a stress period.
Yield response was 1.2t/ha, says Dr Marks.
A further trial during 2021 assessed Zeme’s ability to trigger the crop’s stress response mechanism.
“Could it help the crop under pathogenic attack? Our thinking being that if the plant produced a more robust response, it should also alleviate pressure on the fungicide’s mode of action.”
For this trial, the multi-site component was omitted from a standard fungicide programme and substituted with Zeme.
Assessment in July, pre-senescence, revealed significant septoria reduction on the flag leaf, compared to the standard programme, says Dr Marks.
“That demonstrates how silicon enhances the plant’s ability to resist attack, through tougher plant tissue.
Alleviation of stress effects may also be responsible and even in the absence of stress these mechanisms often demonstrate yield increases.
“What’s particularly pleasing is how this novel silicon formulation works alongside conventional chemistry,” adds Dr Marks.
Ongoing UK and Netherlands trials this year should further understanding of how and where silicon improves crops’ metabolic efficiency.
“Crop yields have plateaued, yet we still need to grow more food, while using fewer resources.
“I’m convinced the answer lies in re-examining our approach to crop nutrition, working out what’s needed to improve not just nitrogen use efficiency, but overall nutrient use efficiency too.
“Silicon won’t be the last nutrient to merit a re-evaluation,” adds Dr Marks.