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How Plants Transform Pollution Into Nourishment · Hydroponics Daily

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Hello there, welcome back to
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Hydroponics Daily, your go-to podcast for everything soilless cultivation.
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I'm your host, Dr. Russell Sharp, and today we're exploring a little-known but
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highly relevant phenomenon, plants directly absorbing pollution and using it as nutrition.
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So now to be clear, we're not talking about nitrogen fixation here,
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there's no microbes involved, no beans or legumes.
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We're not talking about taking nitrogen from the air or carbon dioxide from
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the air, we're talking about the direct uptake of airborne nitrogen oxides,
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ammonia and sulfur compounds, particularly through the leaves and stomata and
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plants using them as nutrients.
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This is something that is not talked about much in plant physiology, plant nutrition.
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You won't hear any other brands talking about it because they want you to buy
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fertilizer and things like this.
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But air pollution is not just a threat to health, human health or climate change.
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And the ecosystem in general, it's becoming a surprisingly significant source
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of plant nutrients, especially in urban and in industrialized areas.
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And so there's a long history of this because air pollution has been around
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for nearly 200 years now, since the industrial revolution.
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And so there's lots of examples of where air pollution has been used by plants.
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So let's unpack how it works, the implications, and what growers need to know
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about how to manage it intelligently.
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We've talked about things like ozone before being an air pollutant that is damaging to plants.
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This is one that is going to be, in most cases, beneficial, but some things
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to look out for to make sure you don't take it over the edge.
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So modern air contains more than nitrogen, oxygen, carbon dioxide,
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and 1% argon. Did you know that?
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Agricultural and industrial emissions contribute to
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sulfur dioxide nitrogen oxides so no
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and no2 which are collectively termed nox
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or nox from vehicle exhausts and
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power stations ammonia from livestock and fertilizer drift and micronutrient
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particles from pesticide drift and dust things like many of the fungicides used
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in orchards contain zinc so if you're growing down in kent and there's loads
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of orchards you You might be getting a fair amount of zinc in the air.
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In the dust. So these compounds can dissolve in leaf moisture or on rain,
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so in the dew, they can bind to airborne dust and many absorb directly through the plant's tomato.
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Especially under humid conditions.
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So how do plants absorb them?
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Well the gases like sulfur dioxide and ammonia, when they touch the leaf surface,
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the sulfur dioxide is oxidized into sulfite and
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sulfate and they're what plants can use as a nutrient the
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NO and NO2 are converted to nitrates and we all
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know that nitrates are what's in fertilizer and the
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ammonia dissolves as ammonium so
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things like ammonia the NO and the NO2 combined with the ammonia that'll convert
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to something like ammonium nitrate which is a common fertilizer so plants absorb
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and metabolize these just like nutrients from roots and just like a foliar fertilizer
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and this is where it gets interesting.
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Recent estimates suggest that in Europe, up to 25 kilos per hectare of nitrogen
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is deposited onto farmland annually through air pollution.
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That's a real and measurable part of the nutrient budget.
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It's like a big bag of ammonium nitrate being, well, even more than that,
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because ammonium nitrate is not pure nitrogen.
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It's like two or three bags of ammonium nitrate per hectare.
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That's not an insignificant amount.
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The impact this added nitrogen and sulfur can skew nutrient
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ratios plants may show luxury nitrogen
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uptake even without root application sulfur inputs
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from sulfur dioxide and rain can replace or complement
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sulfur fertilizers now in europe the amount of sulfur in the air has actually
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gone down because of the reduction in coal-fired power stations and so we're
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finding in agriculture they have to put more sulfur into the fertilizers and
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And I've spoken to a few fertiliser companies in the UK and they're saying, you know,
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we really value sulfur and we try and get as much sulfur into the product as possible.
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So Cali-Semen at Shogun, as we've talked about that in the past,
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and certainly Utrema, we really
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value products that contain sulfur because there's less sulfur around.
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Whereas a lot of the old school fertilisers were developed when there was plenty
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of sulfur coming from the air.
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So plants weren't showing symptoms of it. Farmers in urban areas must probably
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factor that in when formulating fertigation because there's a move now to urban
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farms and things like this, like in Detroit and places like this where there's
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abandoned areas of land.
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You can have more sulfur, more nitrogen, and more ozone damage.
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So that's not a nutrient.
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If your crops are consistently high in nitrogen, despite low applications,
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the air might go fertilizing them for you.
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So what's the hidden risk of too much nutrition? Well, a boost of sulfur and
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nitrogen can help, but if you add too much, sulfur will always burn,
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and nitrogen can burn, ammonia can burn.
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You get tit burn, chlorosis. You can disrupt beneficial fungi,
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including mycorrhiza, sulfur especially.
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Sulfur turns to sulfuric acid in high doses and so that will damage fungi particularly.
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Prolonged exposure will damage your leaves. If you burn sulfur in a greenhouse
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and you've got plants there then you'll know that that will damage leaves because
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it'll just be far too acidic and it might shift to the microbial balance in favour of pathogens.
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So one study showed that sulfur pollution can suppress beneficial fungi and
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promote disease causing types. So that's a lose-lose situation.
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So are certain plants better at absorbing pollution than others? And certain plants can.
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They've evolved to actively benefit from air pollution.
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So Magnolia cobus and Eucalyptus viminalis can derive over 10% of their nitrogen
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from NOx gases in urban environments.
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That's interesting because magnolia are considered quite a primitive tree species
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as eucalyptus that's antipodean not
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much pollution down in australia is there in the outback so
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that opens a fast fascinating opportunity could these species be harnessed could
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we could scientists study these more these plants that are particularly good
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at absorbing pollution and plant them in urban and roadside gardens to capture
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nitrogen and thrive and grow even faster remember this is not nitrogen fixation
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they're absorbing nitrogen oxides directly from the atmosphere,
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not atmospheric nitrogen gas, which is not a pollutant. What about dust and micronutrients?
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In nutrient-poor regions like deserts, airborne dusts become a major nutrient
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source, carrying phosphorus, potassium, calcium, and magnesium,
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and trace elements from synthetic fertilisers, industrial activity, and road dust.
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So factories giving out things they shouldn't into the air, which they do and
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have to be caught and prosecuted, things like this.
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So zinc and copper can enter systems via pesticide use,
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especially in fruit crops as i've said things like mancozeb contain these
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these micronutrients think of bordeaux mixture and
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various copper products that are used on vineyards so
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every single copper first copper pesticide is
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banned in the uk now apart from on grapes so around vineyards then they could
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be used there's lots of vineyards near me in brooksworth in northamptonshire
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and so there could be zinc and copper in the air around there and then around
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the world copper is used on vineyards unfortunately because it's a horrible
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dangerous toxic chemical heavy metal so.
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But we think of like the drift from deserts, you know, it wouldn't affect us
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here in England, but actually it does.
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We do get sand from the Sahara drifting in on various weather conditions and
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cars get covered in it and things like this.
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So, and especially in Spain and places like that and Tenerife,
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you know, people with lung problems in Tenerife, go on a holiday to Tenerife
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in the winter and can actually make it 10 times worse because of the dust coming in from the Sahara.
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So it travels a long way, desert dust and its nutrients.
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So and then we've got rising co2 levels and
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don't just impact climate they influence root behavior
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and plant growth high co2
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levels make plants release more root exudates and
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these help these root exudates are there to help chelate nutrients
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and acidify the soil and activate microbial communities
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so higher co2 levels you might not you might
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think don't impact nutrient levels but they will in
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hydroponics this could influence your biofilms
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and your substrate chemistry and your nutrient demand could actually
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need higher nutrients when you're when you're supplementing co2
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often you'll find
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self-appointed experts on facebook and things saying that oh
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co2 levels are rising so plants will grow faster and
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yields will be higher and you're like it's not all bad
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climate change or global warming which is
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a very old phrase um but they're absolutely complete
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effing idiots aren't they because they don't realize that
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weeds grow faster than crops when high when elevated co2
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levels so we'll have to put more herbicide down it's not
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a case of climate change improves yield it's it
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just makes everything harder at the moment it's 30 degrees
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sea outside and i'm pretty certain the farmers are not happy that.
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It's 30 32 degrees celsius in the
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uk when they're trying to grow their crops so anyway
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back to what does air pollution mean for hydroponics urban
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hydroponic growers especially rooftop or greenhouse setups
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may experience unexpected nutrient trends excess nitrogen
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or sulfur if they're measuring it further uptake of
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micronutrients but probably that's going to be positive for
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the plants but negative for anyone who's living in those urban environments
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and then you might get if you need live near a
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factory that was releasing ammonia which it shouldn't do because they should
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have ammonia scrubbers whenever they're using ammonia or sulfur near a power
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station a coal-fired power station then or a busy road industrial site livestock
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operation you might get ph shifts from just too much ammonia or sulfur so they might reduce the ph.
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I think that's been a big problem in China where ammonia is not controlled as
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much coming from factories and they've had issues with crops getting too much
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ammonia and then you know massive,
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I saw a green tech I saw this massive factory where
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they grew hydroponic grass for
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pigs and yeah imagine a massive pig
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farm like those industrial pig farms that look they look like skyscrapers are
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actually pig farms yeah imagine the amount of
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ammonia coming off them if you had a hydroponic setup next to them you
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might have ammonia issues so you can check for ammonia
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sulfur dioxide knocks in your environment but it is quite difficult you might
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be able to get some details on pollution levels in your area in the uk we have
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sensors all around major cities to test for pollution levels because there's
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legal limits that are set and often these go over,
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with electric cars though it's not
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a case of them reducing pollution but they're certainly getting the pollution out
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of the urban areas moving towards bicycles and public transports with less diesel
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particles and petrol engines in city centers the pollution will move towards
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where the power stations are and not into the city streets so you we potentially could have less,
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air pollution and less air nutrients in city centres and urban environments soon.
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You could adjust your fertilizer inputs, but you're probably not going to know
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that it's due to air pollution.
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It's probably just going to be something you get used to and you know your local
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systems and you know your nutrient levels.
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You're not going to say, oh, we've got high air pollution today.
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I'm not going to put as much nitrogen on. I'm not kidding you that that's going
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to be anytime soon that people are going to do that.
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As always, always wash your foliage, remove dust
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and residues especially if you've got you live in an environment
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where you know there are diesel particles and and and
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pollution but anyway it's always good to do that because you might you might
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have spilt some fertilizer solution or some biostimulant on the leaves and you
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might have got some bacteria growing on it or on the on the leaves and if you
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eat that even if it's non-pathogenic it could still give you an upset stomach
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so always wash your foliage especially,
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plants that you don't cook before you eat
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like lettuce cucumber strawberries and
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always wash things like lettuce because they've got
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such a high surface area to volume ratio so when it goes into your stomach it's
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harder for your acids to completely sterilize it that's why you when you go
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on holiday you should never eat lettuce especially for the first week because
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your body hasn't become accustomed to the local microflora that might be on
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the lettuce and And if you're going to get poisoned, lettuces are really...
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Common reason for that they say you should eat cucumbers
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and tomatoes and things like this if you want fresh food but there's one
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issue with that and that is those fruits
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and are cut before you
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eat them and so that knife has to be clean otherwise
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it's just spreading germs across so probably your best bet is
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a whole tomato or a whole cucumber or something
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like that like you know a snack cucumber they're probably the the
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least way to get food poisoning or pollution when
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you're abroad that's off topic a bit there really making sure
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how to not get food poisoning when you're abroad is
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pretty off topic for an episode you could potentially
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use intake filters to prevent pollution coming into
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your grow room but they would have to be very very fine mash
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and that's only going to exclude the dust you'd have to have a type b filter
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to remove ammonia and sulfur dioxide and nox carbon filter you could have a
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carbon filter on your inlet that would help if you had a big issue if you were
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right next to a pig farm or a chicken farm then.
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You could do that the village iman's got a big
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pig farm and that sometimes i wake up to the
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smell of pig manure it's lovely isn't it smells of the countryside industrial
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levels of pig production maybe i should have a carbon filter on my inlet into
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my house and so yeah i wouldn't avoid applying nitrogen sulfur because you're
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in an urban environment i would still think that you better always to apply
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a bit more sulfur and nitrogen certainly sulfur than you're going to need because.
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Deficiencies will really limit your crop and will be the first
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thing that come across so the air your plants breathe could be
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feeding them or stressing them by understanding how nitrogen sulfur
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and dust interact with plant nutrients you could
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potentially tune your system or be more precise or certainly
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know when issues could arise in certain situations where issues
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could be caused if you go to see a grow and it's
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near to a very busy road or it's near to a chicken farm
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or a factory then you could say perhaps
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it's the air pollution coming in from there that is
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causing either a bumping yield or a stress condition
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maybe you've got burning on the tips of your leaves so just
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a thought it's not a massive issue i'm not saying this
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is the number one issue in hydroponics or it's something you should be
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lying up awake at night thinking about
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but it's just interesting isn't it you know the fact that your plants could absorb significant
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amounts of nutrition like imagine those three bags of fertilizer 25 kilo bags
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or my body weight i wish and in nitrogen being applied as fertilizer for every
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hectare that's a lot of nitrogen okay that's been hydroponics daily for today
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until tomorrow thank you very much for listening goodbye.