The review highlights complex interactions between soil microbes and viruses that occur on the surface of microplastic particles. These microscopic relationships may influence soil health, ecosystem recovery and the long-term sustainability of agriculture.

Microplastics are plastic fragments smaller than five millimetres that enter farmland through sources such as plastic mulch, sewage sludge, irrigation water and degraded plastic materials.

WHY IT MATTERS: Once in the soil, they can alter physical structure, disrupt nutrient cycling and affect the activity of soil organisms essential for plant growth and ecosystem functioning.

A 2023 study found China is the world’s largest user of microplastic mulches, averaging 17 to 20 million hectares annually or 68 per cent of global usage.

Figures from the Canadian government show Canada produces 60,000 tonnes of plastic waste on farms every year.

The latest research finds microplastics create unique microscopic habitats in soil called plastispheres, biofilm communities where microorganisms attach to plastic surfaces and interact intensely. Within these microhabitats, microbes and viruses form dynamic networks that may reshape microbial communities and influence soil processes.

Bacteriophages are viruses that infect bacteria. They play a central role in these interactions. By infecting and lysing (that is, rupturing the walls or membranes of) bacterial cells, they can regulate microbial populations and influence nutrient cycling. Viral activity can also transfer genes between microbes, including those related to plastic degradation or antibiotic resistance.

The researchers note these viral gene exchanges may have both positive and negative consequences. Viruses may help spread genes that enable microbes to break down plastic more effectively. But they could also accelerate the spread of antibiotic resistance genes or other harmful traits.

Scientists are exploring strategies such as phage-assisted microbial augmentation and virus-like particles loaded with catalytic nanoenzymes. These systems could potentially deliver enzymes directly to plastic surfaces and accelerate polymer breakdown.

The study notes these technologies remain largely theoretical and need careful evaluation before field use. Concerns include biosafety risks, unintended gene transfer and the complex ecological dynamics of natural soil environments.

A lack of long-term field data on how viruses, microbes and microplastics interact over time is also hindering researchers. Most studies rely on laboratory experiments or short-term observations, leaving major knowledge gaps about how these interactions evolve in real conditions.

Emerging technologies such as single-cell viromics, artificial-intelligence-driven host prediction and advanced multi-omics tools could help reveal the hidden viral networks operating in contaminated soils.

Ultimately, the study suggests that understanding the invisible partnerships between microbes and viruses may open new pathways for restoring soil ecosystems affected by plastic pollution.

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What is the impact of wildfire smoke on field crops?

A common question this year has been “what is the impact of wildfire smoke on field crops”? Given the random and infrequent nature of these smoke events, research is limited and it’s difficult to conduct controlled experiments to measure impacts directly.

In absence of research, one approach is to look at characteristics of smoke events (e.g., smoke levels, crop stages affected) to estimate what crop impacts may be (Jeschke, 2021). Several authors have outlined common themes for potential positive and negative impacts of wildfire smoke on crops.

Negative Impacts

Reduced Light Availability
Smoke particles reflect a portion of incoming solar radiation potentially reducing the amount available for photosynthesis at plant level.

How much does wildfire smoke reduce light?

Jeschke (2021) summarized results from a couple of research trials investigating light reductions during wildfire smoke in California which ranged from 4-11% over the period smoke was present. Data from Ohio suggested a 6-7 per cent reduction during June/July when wildfire smoke was present compared to the same period for the previous 5 years (Lindsey, 2021).

How does this compare to cloudy weather?

For comparisons sake, Jeschke (2021) compared measurements of photosynthetically active radiation (PAR) for varying cloud covers relative to a sunny July day in Iowa.

• a partly cloudy day reduced PAR by 23 per cent
• a cloudy day reduced PAR by 52 per cent
• a rainy day reduced PAR by 62 per cent

What are yield impacts for reducing light?

In corn, small amounts of shading can have limited yield impacts, but significant shading can impact yields. Amount of yield loss depends on crop stage. Yield impacts are minimal during vegetative stages and greatest during pollination and early grain fill (likely because kernel number and kernel fill is highly sensitive to photosynthate production at these times) (Jeschke, 2021).

The amount of light we receive may be greater than what plants require to optimize photosynthesis. Reducing light availability is expected to have a greater impact on C4 plants (corn, sorghum) as they have higher light saturation points (the point where additional light provides no more benefit for photosynthesis). Light quantity must be reduced a greater amount before it starts to impact photosynthesis in C3 plants (most other field crops grown in Ontario) (Lindsey, 2023).

Other reduced light risks

If carbohydrate accumulation during grain fill is lower than normal, another potential risk could be increased remobilization from stalks to help fill grain, as can occur during years with other stresses (drought, disease/leaf area loss, N loss etc.). Compromised stalks can increase risks for stalk rots and/or lodging (Archontoulis and Licht, 2023; Jeschke, 2021).

Ozone
Ozone is produced when certain pollutants produced by wildfires react in the presence of sunlight. Ozone enters plants through stomata and damages plant tissues during respiration which can cause growth issues. Dicots (e.g., soybeans and other non-grasses) are thought to be more susceptible than monocots (e.g., grasses) possibly because injury symptoms may be more clearly observed, but yields can be reduced in both (Jeschke, 2021).

Ash deposition
Crops that are in the vicinity of wildfires, could experience ash deposits on leaves and potentially block various amounts of light and photosynthesis (Lindsey, 2023).

Positive impacts

Diffuse light
Smoke particles scatter light which produces diffuse light (light received indirectly after bouncing off objects rather than directly from the sun). Diffuse light can penetrate deeper into crop canopies and provide light for photosynthesis to lower leaves which are shaded under sunny conditions. Because photosynthesis may not use all light provided (Lindsey, 2023) this may increase total photosynthesis in the crop canopy if the increase in total photosynthesis is greater than any decreases in light received from what is causing diffusion (cloud, smoke). Some greenhouses use diffuse covers to scatter light on sunny days for this purpose. Canopies with greater heights or leaf area indexes likely see the greatest benefits from diffuse light (Jeschke, 2021).

Lower leaf temperatures
Leaf temperatures are more related to light intensity than air temperature and lower light intensity can reduce leaf temperatures (Lindsey, 2023). This can reduce plants reliance on transpiration to cool leaves. Preserving moisture can be a benefit under sunny, hot and drought-stressed conditions.

Final comments

There can be both potentially positive and negative impacts, but they are complex, depend on degree of smoke, crop growth stage, and potentially interact with each other (Jeschke, 2021). It’s difficult to put exact numbers on yield risks. While it can’t be said wildfire smoke has no impact, other factors such as drought or excess rainfall can have much more significant impacts on yields, and other areas of North America have been able to achieve record yields in years where wildfire smoke was apparent during parts of the growing season (Archontoulis and Licht, 2023).

In Ontario, on the favourable side this year, most smoke was encountered during the vegetative stages for crops like corn and soybeans, when impacts from potential negative factors are likely much less.

– This Ontario Field Crop Report was originally published at the Field Crop News website.

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These chemicals are a group of artificial compounds based on carbon and fluorine – per- and polyfluoroalkyl substances, or PFAS. They comprise thousands of individual chemicals with hundreds of documented uses, including water proofing and fire suppression. It is likely every household has products or textiles that contain or were treated with a product that contained PFAS (including some non-stick cookware and stain-resistant fabrics).

Studies have shown most people have one or more PFAS compounds in their blood. We live in a world full of chemicals, so why do we care about these ones? Well, some PFAS have been associated with a wide range of adverse human health effects, such as cancer and immune problems. However, there is limited evidence of human disease resulting from environmental exposures.

Our study investigated the uptake of PFAS into livestock at ten PFAS-impacted farms in Victoria, Australia. Our analysis also shows how risks can be reduced.

Our findings show the land and livestock can be managed to reduce PFAS levels in the animals before they enter the food chain. This means good management practices can protect food quality and reduce consumer exposure.

Exposure to household dust and consumption of contaminated food or water are major contributors to human exposure to PFAS. It then accumulates in our blood.

As the name would suggest, forever chemicals persist in the environment. As a result, when released into the environment, they disperse and over time can contaminate surrounding areas.

Firefighting and training activities have historically resulted in large releases of PFAS into the environment. This includes farming areas.

As livestock feed and drink from contaminated sources, this leads to PFAS accumulation in tissues. From there, PFAS can be transferred into the food chain, including products we eat such as meat and milk.

The causal links and what levels of PFAS exposure are harmful are still being investigated. The scientific community has yet to reach a consensus on how “bad” these compounds are, or conversely what the safe exposure levels are.

In the meantime, it is important to limit exposure through regulation. Australia has adopted environmental and health-based guideline values for three PFAS of concern: perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonate (PFHxS).

Australian food quality is high. In a 2021 study, scientists tested for 30 different PFAS in a broad range of Australian foods and beverages. Only one specific PFAS (PFOS) was detectable. It was found in just five out of 112 commonly consumed foods and beverages at levels below concern.

These findings would suggest PFAS contamination is not an issue at most farms in Australia. The risks are likely to be higher from food produced at PFAS-contaminated sites. At such locations, PFAS can affect a range of foods, including eggs, vegetables and livestock.

We collated data from environmental investigations at 10 PFAS-impacted farms in Victoria. This included testing about 1,000 samples of soil, water, pasture and livestock blood for concentrations of 28 types of PFAS. Our analysis also included information about farm practices, including livestock rotation, access to clean pasture and water.

We found:

• two specific PFAS compounds (PFOS and PFHxS) made up more than 98% of total PFAS detected in livestock blood
• PFAS concentrations in water were correlated to concentrations in livestock blood, implying water was a critical exposure pathway, while the relationships between livestock and PFAS levels for soil and pasture were weaker
• livestock exposure to PFAS varies over time and across paddocks. Seasonal patterns in PFAS blood concentrations were linked to seasonal grazing behaviours and the animals’ need for drinking water.

Environment Protection Authority Victoria (EPA) is leading research and policy to understand how environmental PFAS risks can be better managed. In this regard, EPA along with research partners, is working to develop predictive models to estimate PFAS accumulation in livestock over their lifetime.

This research will help determine when a site is too contaminated for livestock production and which ones to prioritise for PFAS remediation in soil and water.

Ultimately, this will allow more effective management of PFAS accumulation and reduce the likelihood of having PFAS for dinner.

This first appeared at The Conversation theconversation.com.

– Antti Mikkonen is with the University of South Australia and Mark Patrick Tayler is with Macquarie University.

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The database is also expected to help countries and regions evaluate their performances in addressing phosphorus pollution and scarcity challenges, and guide actions toward a more sustainable future.

“To address these management challenges, it is critical to use phosphorus more efficiently in agriculture,” said lead study author Tan Zou. “Knowing these gaps and potential drivers can help to guide the development and implementation of best management practices, such as soil testing and specialized fertilizers that are better absorbed by crops.”

Phosphorus is an essential nutrient for crops and living organisms, but excess phosphorus that runs off agricultural fields and into bodies of water has led to harmful algal blooms and low oxygen zones that are detrimental to aquatic ecosystems. 

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Poor nutrient management can lead to nutrient waste, loss or shortage, resulting in social and environmental problems such as environmental pollution and crop yield reduction.

“The dominant global challenge is to enhance crop yield while bringing human disturbance of phosphorus cycles back to the planetary boundary,” said Zou. 

“This could be achieved by developing and implementing more efficient nutrient management practices and allocating production and input resources to regions with higher phosphorus use efficiency levels.”

While many efforts have been devoted to improving nutrient management practices on farms, few studies have examined the historical trends of phosphorus use efficiency and their socio-economic and agronomic drivers on a national scale. 

This is the first study to present a database of agricultural phosphorus budgets and phosphorus use efficiency by country, year and crop type. It examines the contribution of several socioeconomic drivers and discusses phosphorus management challenges and opportunities in cropland by country. 

Phosphorus management challenges and opportunities in croplands vary widely among countries and are related to multiple socio-economic and agronomic factors, such as economic development stage, nitrogen use efficiency and farm size. Recent levels of phosphorus loss from cropland have exceeded a proposed planetary boundary, highlighting the need for more efficient use of phosphorus fertilizer to reduce environmental damage while securing future food supplies. 

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To meet the predicted food demand in 2050,while bringing the phosphorus surplus level below the planetary boundary, global phosphorus use efficiency must be improved to about 70 to 80 per cent, researchers said.

“While nutrient management practices are typically carried out on farms, decisions by stakeholders along the food supply chain largely determine which crops are being produced and how much is lost from the farm to the fork,” said co-author and UMCES professor Eric Davidson.

The challenge of phosphorus scarcity is more concerning for countries that have limited reserves, such as India and Mexico. All countries that rely upon imported fertilizers need to consider their vulnerability to geopolitical events, such as those in Ukraine, that could affect fertilizer and food trade and identify alternative sources, said researchers.

“The price of phosphorus and nitrogen fertilizer is at an all-time high, potentially exacerbating the ‘too much, too little’ dilemma. While part of the world is applying ‘too much’ nutrient fertilizers causing pollution, the other part of the world is struggling with the lack of accessible and affordable fertilizer to support the production of basic nutrition needs by the population.

“Addressing such dilemma is essential for achieving sustainable development goals and requires collaboration across countries,” said co-author and UMCES associate professor Xin Zhang.

By examining historical trajectories of phosphorus budgets for crop production by country and crop type in the past five decades, the work shows a common trajectory of phosphorus use efficiency as countries develop their economies and intensify crop production.

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