Soil and Fertilizer

The Downside of Fertilizers

In a belated celebration of Earth Day, this fourth in our April series on soil focuses on the negative side effects of various soil amendments and on hopeful signs we can do better. We are all familiar with the phenomenon of eutrophication, algal blooms that overwhelm waterways when too much phosphorous runs off from agricultural operations. Nitrogen fertilizers also can easily volatilize, leading to emissions of nitrous oxide, which has hundreds of times the warming potential of CO2. However, as the second article below details, the exploitation of these resources has led to human rights violations as well as environmental degradation. The example of the Rich Earth Institute offers hope that we may be able feed a growing population without destroying the planet in the process.

Reducing nitrogen use key to human and planetary health: study

The use of chemical fertilisers helped fuel the four-fold expansion of the human population over the last century.

Better management of nitrogen-rich fertilizers through alternating crops, optimizing use and other measures can yield huge environmental and health benefits, but must boost food production at the same time. Reducing nitrogen pollution from global croplands is a “grand challenge,” the group of international researchers said in a study published in Nature outlining a dozen urgently-needed reforms.

The intensive use of chemical fertilizers helped fuel the four-fold expansion of the human population over the last century, and will be crucial for feeding 10 billion people by 2050. But the bumper crops of what was once called the Green Revolution have come at a terrible cost. Today, more than half the nitrogen in fertilizers seeps into the air and water, leading to deadly pollution, soil acidification, climate change, ozone depletion and biodiversity loss.

Earth’s natural “nitrogen cycle” has been massively imbalanced by the use of some 120 million tons of chemical fertilizer each year. Less than half of that input is actually absorbed by plants, with the rest seeping into the environment and causing a constellation of problems. Researchers led by Baojing Gu, a professor at Zhejiang University, analyzed over 1,500 field observations from croplands around the world and identified 11 key measures to decrease nitrogen losses while still enhancing crop yields. One such method is crop rotation where a variety of crops are planted on the same plot of land, optimizing the flow of nutrients in the soil. The benefits of slashing agricultural nitrogen pollution are some 25 times higher than the implementation costs of about $34 billion, they found.

Phosphorus Saved Our Way of Life—and Now may End It

Bou Craa conveyor belt from the phospahe mine. Photo from flickr, taken on 11 March 2013 in Western Sahara near Laayoune Marsa Boujdour. Photo by jbdodane.

Like nitrogen, phosphorous soil amendments were an important part of the Green Revolution that enabled us to feed so many more humans. And like nitrogen amendments, using phosphorous as a soil amendment comes with unanticipated costs. Writing in The New Yorker, Pulitzer Prize winning author Elizabeth Kolbert details the sordid colonial history of guano exploitation in Peru and South Pacific Islands. Once the accumulated bird poop of thousands of generations had been consumed by farmers in Europe and the US, and the nesting sites of many birds destroyed, science stepped in to invent chemical ways to extract nitrogen from the atmosphere and phosphorous from rock. As Kolbert writes: ” The longest conveyor belt on earth begins in the town of Bou Craa and runs for sixty miles across Western Sahara to the port city of El Marsa…. The conveyor carries phosphorus-rich rock, which is mined in Bou Craa and then shipped from the coast to places like India and New Zealand to be processed into fertilizer. The mine, and indeed the vast majority of the rest of Western Sahara, is controlled—illegally, by most accounts—by Morocco, which possesses something like 70% of the planet’s known phosphorus reserves.”

The political fragility of Western Sahara is just one worrying aspect of the future of phosphorous use. Phosphorus is critical not just to crop yields but also to basic biology. DNA is held together by what’s often called a “phosphate backbone”; without this backbone, the double helix would be a hash. Isaac Asimov described phosphorus as “life’s bottleneck.” What distinguishes it from other elements that are essential to life—carbon, say, or nitrogen—is its relative scarcity. The atmosphere contains almost no phosphorus. Phosphate-rich rocks, meanwhile, exist only in limited quantities, in certain geological formations. China holds the world’s second-largest reserves—these are less than one-tenth the size of Morocco’s—and Algeria the third-largest.

There are parallels between the exploitation of guano in the 19th Century and phosphorous in the 20th Century. The Bou Craa mine is the main reason Morocco illegally invaded Western Sahara in 1975. The descendants of tens of thousands of refugees from Western Sahara are still living in refugee camps in Algeria today. Meanwhile, phosphorous use in agriculture has led to increasing large “dead zones” in waterways and oceans around the world. Harmful algal blooms caused by phosphorous leaching into waterways can also contaminate water supplies and cause illness. Scientists warn that, as nutrient loads continue to grow and the planet heats up, the problem will only get worse.

The Rich Earth Institute in Brattleboro, Vermont, works for “a world with clean water and fertile soil achieved by reclaiming the nutrients from our bodies”.  The Institute encourages donations of urine from the local community. Arthur Davis, who directs Rich Earth’s Urine Nutrient Reclamation Program, explains, “Around 60% of the phosphorus we excrete comes out in our pee.” Peecycling can cut down on the amount of conventional fertilizer that the farmers purchase. (Urine contains not only phosphorus but also large amounts of nitrogen and potassium.) At the same time, it keeps nutrients out of the sewage system and, by extension, it is hoped, out of Vermont’s waterways. It may also help to avoid some of the human and environmental rights violations associated with the historical exploitation of phosphorous.

Credit: Unsplash/CC0 Public Domain

(See also: Phosphorus shortage could affect worldwide crop yields)

Soil and Fertilizer

Soil Amendments & Fertilizer

The third in our April series on soil and fertilizer, this post explores the value of composting, manure – and humanure! – as a soil amendments, as well as looking at other kinds of soil amendments.

Waste not want not: Santiago’s poorest district plants recycling seed

Municipal staff collect organic material to be sent for a vermiculture recycling process in the commune of La Pintana in Santiago, Chile.

Every morning, trucks collect potato and avocado skins, orange peels and other food scraps that residents of Santiago’s poorest neighborhood leave hanging in bags on their front doors or in tree branches or place in special bins. For nearly two decades, the residents of La Pintana have been pioneers of recycling in Chile—South America’s largest garbage generator. Under a project started in 2005, the commune of 190,000 people enthusiastically gather their plant-based food waste, which is then turned into compost to help green their community.

In La Pintana, where 15% of people live in poverty, 50% of the community’s organic waste is collected for recycling—a figure that puts to shame the 0.8% achieved by Chile as a whole, according to environment ministry data. “They do a lot with it (the waste): they produce compost and it is used for the community itself, for the squares and gardens,” La Pintana resident Jose Vera told AFP as he left two large cardboard boxes filled with scraps on the sidewalk, proud of his contribution. “It is also a saving (for the municipality) because they no longer have to buy” fertilizer or pay landfill fees, he said.

Chile generates some 1.13 kilograms (about 2.5 pounds) of waste per person per day—the highest output in South America, according to World Bank data. (Note: for reference, a 2013 study suggests that Canadians produce more garbage per capita than any other country on earth. Canadians generate approximately 31 million tonnes of garbage a year and only recycle about 30% of it. Thus, each Canadian generates approximately 2.7 kg of garbage each day.)

The municipality estimates to be saving some $100,000 per year—money that can go to other community projects. “There has been a change in people,” since the project started, resident Vera said. “They are now concerned about recycling and no longer put the vegetables with the garbage.” La Pintana’s nursery, built on what used to be an unsightly landfill, yields some 100,000 plants of 400 different species every year. These are planted back in La Pintana, one of the areas of Santiago with the fewest green spaces per inhabitant.

La Pintana’s nursery, built on what used to be an unsightly landfill, yields some 100,000 plants of 400 different species every year.

Planting flowers outside a municipal sports center, municipal worker Jeanette Gonzalez told AFP the project “brings us… joy. The town is improving.” “It is a virtuous circle: people see that where there used to be a landfill there is now greenery and everything is flourishing, and they stop throwing garbage there,” she added. There have been spillover benefits too: more than half of the municipal nursery’s 15 staff are former inmates doing community work in lieu of serving prison time. Chile’s Environment Minister Maisa Rojas recently proposed a bill to reproduce the project in the rest of Chile.

(See also: Impoverished Chilean neighbourhood’s pioneering waste recycling scheme unites community; and In an impoverished Chilean suburb, a recycling drive flourishes)

Our toilets as alternatives for widespread polluting fertilizers

Notwithstanding concerns we saw in yesterday’s post about the impact of contaminants in manure, several recent articles have highlighted its potential as a replacement for expensive chemical fertilizers.

Image courtesy of The Humanure Handbook.

To tackle the climate crisis, biodiversity loss, and pollution, humanity will need to move to a circular economy, where all resources are recycled. Why not recycle our own body waste too as fertilizer, provided there is no risk that harmful microbes or traces from pharmaceuticals end up in the consumed crops? Most nutrients needed for plant growth occur in human urine and feces. Urine is especially rich in nitrogen and potassium, and also contains trace amounts of metals such as boron, zinc, and iron. Feces could in theory supply other nutrients such as phosphorus, calcium, and magnesium or valuable organic carbon to soils.

Now, a new study in Frontiers in Environmental Science has shown that modern ‘green’ products recycled from human excreta are excellent—and importantly, safe—fertilizers for agriculture. First author Franziska Häfner, a Ph.D. student at University of Hohenheim, Stuttgart, Germany, said, “Here we show that products derived from recycling human urine and feces are viable and safe nitrogen fertilizers for cabbage cultivation. The fertilizers from nitrified human urine gave similar yields as a conventional fertilizer product, and did not show any risk regarding transmission of pathogens or pharmaceuticals. The combined application of nitrified urine fertilizers and fecal compost led to slightly lower crop yields, but may increase soil carbon content in the long term, promoting climate-resilient food production.”

The researchers tested two so-called ‘nitrified urine fertilizers’ (NUFs), modern products synthetized from human urine that has been collected separately from feces, in which nitrogen-bearing compounds are converted by microbes into valuable ammonium and nitrate. These products were found to perform slightly better in field trials than plots fertilized by fecal compost alone. The authors also screened for the presence of 310 chemicals in the fecal compost, from pharmaceuticals to rubber additives, flame retardants, UV filters, corrosion inhibitors, and insect repellants. Only 6.5% of these were present above the limit of detection in the compost, albeit at low concentrations, including 11 pharmaceuticals. Among the latter, only the painkiller ibuprofen and the anticonvulsant and mood-stabilizing drug carbamazepine were detectable in the edible parts of the cabbages, at markedly low concentrations (between 1.05 and 2.8 μg per kg). This means that that more than half a million cabbage heads would need to be eaten to accumulate a dose equivalent to one carbamazepine pill.

Lead author Dr. Ariane Krause, a scientist at the Leibniz Institute of Vegetable and Ornamental Crops in Großbeeren in Germany, said, “If correctly prepared and quality-controlled, up to 25% of conventional synthetic mineral fertilizers in Germany could be replaced by recycling fertilizers from human urine and feces. Combined with an agricultural transition involving the reduction of livestock farming and plant cultivation for fodder, even less synthetic fertilizer would be necessary, resulting for example in lower consumption of fossil natural gas.”

Brown gold: the great American manure rush begins

Hundreds of dairy farms across California have sold the rights to their manure to energy producers. Illustration: Ricardo Cavolo/The Guardian

On the other side of the pond, Jessica Fu reports for The Guardian UK on how US farms are selling their manure to energy firms. The energy industry is transforming mounds of manure into a lucrative “carbon negative fuel” capable of powering everything from municipal buses to cargo trucks. To do so, it’s turning to dairy farms, which offer a reliable, long-term supply of the material.  

Algae as sustainable fertilizer

Credit: Pixabay

Current chemical fertilizers often used in the agricultural industry are not all absorbed by the plants due to the quantities used, leading to some of them being washed away into water bodies such as lakes when it rains. This then encourages algae to grow, which can cause other plant life in lakes to die due to a lack of sunlight and oxygen. New research, published in the Chemical Engineering Journal and led by The Department of Chemical and Biological Engineering’s Dr. Seetharaman Vaidyanathan, found that different strains of algae from a similar habitat can absorb varying amounts of phosphates and nitrates—key nutrients in fertilizers that also encourage algae to grow—potentially from wastewater streams before they get to lakes.

Coir, peat or pine bark – which is best?

A flow chart depicting the wetting up and drying down cycles of substrates evaluated in this study. The wettability of each substrate was tested at each moisture content framed within hydration cycles 1 and 2. Credit: HortScience (2022). DOI: 10.21273/HORTSCI16698-22

Gardeners seeking alternatives to peat will be interested by this work. The objective of a recent study published in HortScience was to quantify the sorptive effects on substrate wettability and water-holding capacity. Inferences into the effectiveness of the substrate to capture water have been difficult to demonstrate statistically. To assist in this, researchers used a monomolecular exponential model to quantify water holding capacity and the irrigation volume required to reach that capacity. Because the wetting behavior of peat can be greatly affected by hydrophobicity, a second objective was to determine the effectiveness of hydrophilic coconut coir in mitigating the initial hydrophobicity of a peat substrate.

The substrate materials tested were a 6-month aged loblolly pine bark, sphagnum peat moss, and coconut coir. Data from these experiments provide evidence that the moisture content and preconditioning of a substrate can lead to differences in initial water capture efficiency. This information can be critical to growers, growing media manufacturers, and researchers alike. The wettability of peat was most affected by moisture content and the initial wetting and drying cycles. Hydration efficiency was improved in peat by blending in as little as 15% coir by volume.

Image from an article by Green Lawn Fertilizing.

Two other articles dealt in some detail with the science of amendments for specific soil deficiencies.

An article called A nifty trick to help plants thrive in iron-poor soils describes how scientists at RIKEN have determined the structure of a key transporter protein that helps plants gather iron from soil. This work may help to formulate more targeted fertilizer products. The paper was published in the journal Nature Communications. Meanwhile, researchers at Michigan State University are Helping plants grow as phosphorus levels in soil deplete. Plants absorb phosphorus from the soil. When soil doesn’t contain enough phosphorus, plants will take up more iron from the soil, which becomes toxic at increased levels. Previous research supported the idea that iron toxicity caused a plant’s roots to stop growing. Now, for the first time, researchers at MSU and the Carnegie Institution for Science have found evidence that the plant roots stop growing early, without any evidence of iron. This changes the way researchers look at this problem. Their research was published in the journal Current Biology.

Citizen Science Conservation Soil and Fertilizer

The Dirt on Soil

Continuing our soil theme from yesterday, today’s post focuses on pollutants in soil.

Map of the study area and watersheds near village Kibber in the high-altitude region of Spiti, Trans-Himalaya, northern India. The colored polygons represent eight watersheds spread over c. 40 km2. The native and livestock watersheds are demarcated by high ridges, escarpments and ravines, that establish replicates of two types of herbivore-assemblages (dominated by either livestock or by native herbivores). Credit: (2022). DOI: 10.1101/2022.02.07.479355

Antibiotic-laced dung ‘harming soil quality’

Antibiotics used on livestock can impact microbes in the soil and negatively affect soil carbon, reducing resilience to climate change, claims a study conducted in India’s trans-Himalayan region. Results of the study, published in Global Change Biology, found native herbivores such as yak, bharal (blue sheep), kiang (wild ass) and ibex in the Spiti valley, in India’s Himalayan state of Himachal Pradesh, to be healthier for soil carbon than livestock, which includes cattle, goat, sheep and horse. “Microbial carbon use efficiency was 19% lower in soils under livestock,” said Sumanta Bagchi, an author of the study and assistant professor at the Center for Ecological Sciences of the Indian Institute of Science in Bangalore.

Supporting evidence in the study pointed to a link between veterinary antibiotics and soil microbial decline. “Our study suggests that conserving native herbivores together with better management of livestock can go a long way towards improved soil carbon stewardship to achieve natural climate change solutions,” says Bagchi. “Our paper focused on climate impacts linked to the use of antibiotics for livestock rearing but there are other undesirable consequences such as the accelerated evolution of antibiotic resistance which is a global trend,” they added.

Home ‘compostable’ plastic doesn’t fully break down

Compostable plastic that has not fully disintegrated in compost bin. Credit: Citizen scientist image from

In a UK-wide study, researchers have found that 60% of home-compostable plastics do not fully disintegrate in home compost bins, and inevitably end up in our soil. The study also found that citizens are confused about the labels of compostable and biodegradable plastics, leading to incorrect plastic waste disposal. These results highlight the need to revise and redesign this supposedly sustainable plastic waste management system.

A new OECD report shows that plastic consumption has quadrupled over the past 30 years. Globally, only 9% of plastic waste is recycled, while 50% ends up in landfills, 22% evades waste management systems, and 19% is incinerated. Compostable plastics are becoming more common as the demand for sustainable products grows. The main applications of compostable plastics include food packaging, bags; cups and plates, cutlery, and bio-waste bags. But there are some fundamental problems with these types of plastics. They are largely unregulated, and claims around their environmental benefits are often exaggerated.

In a study published in Frontiers in Sustainability, researchers at University College London have found that consumers are often confused about the meaning of the labels of compostable plastics, and that a large portion of compostable plastics do not fully disintegrate under home composting conditions.

Soil pollution in natural areas similar to urban green spaces

Microplastic debris. Credit: Roberto Ruiz (UA)

An international study, recently published in Nature Communications, shows that soil in urban green spaces and natural areas share similar levels of multiple contaminants such as metals, pesticides, microplastics and antibiotic resistance genes around the world. Soil contamination is one of the main threats to the health and sustainability of ecosystems. The work was carried out by more than 40 authors from research centers and universities in Spain, China, Switzerland, Australia, Germany, Chile, South Africa, Nigeria, France, Portugal, Slovenia, Mexico, the United States, Brazil, India and Israel. The team has collaborated with ecologist Carlos Sanz Lázaro and Nuria Casado Coy, researchers at the Ramón Margalef Multidisciplinary Institute for Environmental Studies (IMEM), and experts in the study of plastic and bioplastic pollution.

As the article reports, soil pollution is currently associated with vehicle emissions, industrial processes, pesticide treatment and plant diseases, as well as poor waste management. It is therefore to be expected that urban green spaces are more influenced by pollutants than natural ecosystems, which are geographically distant from human activities. However, the study has shown that hazardous pollutants (metals, pesticides, microplastics and antibiotic resistance genes) can be dispersed by air transport, uncontrolled waste disposal and even rainwater running off the surface of a piece of land and into natural ecosystems.

Microplastics, typical pollutants of anthropogenic (human) origin, are also ubiquitous in soils of urban green spaces and natural ecosystems around the world. Surprisingly, as reported by Sanz Lázaro, they have found similar proportions of the form and polymer type of microplastics in natural areas and urban green spaces, which further supports the idea of a spread of anthropogenic pollutants through ecosystems. These microplastics, often originating from cities, affect distant areas by atmospheric transport, with fibers being the main form of plastic particles suspended in the atmosphere in cities such as Paris, London and Dongguan (China). The fibers generally consist of polyester and polypropylene from synthetic fabrics, ropes, and nets.

(See also: From cities to uninhabited areas: Soil pollution is everywhere)

Biodiversity Soil and Fertilizer

Life in the Ground ~ Soil Biota

Over the next few posts, I’ll be trying to catch up on the many articles I’ve collected about soil.

Samples were harvested at two time points in July and October 2019 at two long-term warming experiments, SWaN and PH, at the Harvard Forest long-term ecological research station, which had been established for 13 and 28 years, respectively. Credit: Global Change Biology (2022).

How are soil microbes affected by climate change?

The largest terrestrial carbon sink on Earth is the planet’s soil. One of the big fears is that a warming planet will liberate significant portions of the soil’s carbon, turning it into carbon dioxide (CO2) gas, and so further accelerate the pace of planetary warming. A key player in this story is the microbe, the predominant form of life on Earth, and which can either turn organic carbon—the fallen leaves, rotting tree stumps, dead roots and other organic matter—into soil, or release it into the atmosphere as CO2. Now, an international team of researchers led by the University of Massachusetts Amherst has helped to untangle one of the knottiest questions involving soil microbes and climate change: what effect does a warming planet have on the microbes’ carbon cycling? The answer is surprising: increased temperature decreases the rate at which soil microbes respire CO2—but only in the summer. During the rest of the year, microbial activity remains largely historically consistent.

But there’s a catch to this seemingly happy story. Soil microbes are releasing less CO2 in the summer because they’re starving. And they’re starving because long-term warming is threatening the viability of deciduous trees, on whose dead leaves the microbes depend. “One of the major outcomes of our study,” says Kristen DeAngelis, professor of microbiology at the University of Massachusetts Amherst and senior author of the study, published in the journal Global Change Biology, “is that all those autumn leaves mitigate the negative effects of global warming on soil microbes.” For now. But fewer dead leaves means less food for the microbes and seems to be leading to a reduction in microbial biomass during the summer.

Modelling bacterial diversity of soils

Credit: Pixabay/CC0 Public Domain

A new set of quantitative models that incorporates pH into the metabolic theory of ecology (MTE) has been developed by an international team that includes Penn State assistant professor of plant science Francisco Dini-Andreote. The work is included in a paper published by the Proceedings of the National Academy of Sciences. In general terms, the metabolic theory of ecology links rates of organism diversification (i.e., the metabolic rate of an organism) with the organisms’ body size and body temperature. “Soils are the most complex and biodiverse ecosystems on Earth,” said Dini-Andreote, a member of Penn State’s Microbiome Center. “In soils, microbial diversity plays indispensable roles in the anabolic and catabolic cycles of carbon, nitrogen and sulfur, without which the diversity of life forms—including plants, animals and other microbes—that evolved on our planet would not have been possible. In addition, advancing our ability to predict patterns of soil biodiversity is critical to better understanding how climate change will affect soil functioning and how soil microbes will respond to shifts in temperature and precipitation regimes.”

It isn’t the picky eaters that drive soil microbial metabolism

Soil sample from the Washington State University field site in Prosser, Washington. Credit: Andrea Starr, Pacific Northwest National Laboratory

Interactions among microorganisms in soil lead to the release of nutrients derived from complex organic matter in that soil. This community metabolism creates food for both microbes and plants. However, scientists don’t fully understand the specific nature of many of these interactions. For example, scientists want to know why some microbes are more successful than others and what roles individual members play in their communities. To find out, researchers from Pacific Northwest National Laboratory, Iowa State University, University of Nebraska–Lincoln, and Argonne National Laboratory studied a model microbial community fed with a complex source of carbon and nitrogen commonly found in soils—chitin.

Their findings, published in the journal mSystems, show that certain microbes drive specific steps of the chitin breakdown process, but the most abundant microbes are not necessarily the most important. The model microbial community used in this study included eight soil bacteria—some chitin degraders and some non-degraders. The researchers observed that the species organized into distinct roles when it was time to break down the chitin. Intriguingly, the most abundant members of the model community were not those that were able to break down chitin itself, but rather those that were able to take full advantage of interactions with other community members to grow using chitin breakdown products. The study answers important questions about how complex carbon and nutrient sources are metabolized by interacting microorganisms to support plant and microbial growth in soil ecosystems.

Microbes could be used by farmers as natural fertilizer for poor soil

A hammer and chisel were required to collect samples from the terrain where Barbacenia macranta lives, in this case, exposed rock. Credit: Rafael Soares Correa de Souza/GCCRC

A study published in The ISME Journal identified 522 genomes of archaea and bacteria associated with the roots and soil of two plant species native to the Brazilian montane savanna ecoregion known as campos rupestres (“rocky meadows”). Hundreds of microorganisms hitherto unknown to science were identified, showing that the ecoregion is a biodiversity hotspot and that many new organisms have yet to be described and classified in Brazil.

The discovery could potentially be a basis for the development of biological substitutes for the chemical fertilizers used by farmers, especially those containing phosphorus. “Phosphorus is normally present in the soil, but not always in a form that plants can use. Most of the microorganisms we found make phosphorus soluble so that plants can absorb it,” said Antônio Camargo, first author of the article.

Fungi and bacteria are binging on burned soil

Signs of microbial life in the Holy Fire burn scar. Credit: Sydney Glassman/UCR

UC Riverside researchers have identified tiny organisms that not only survive but thrive during the first year after a wildfire. The findings could help bring land back to life after fires that are increasing in both size and severity. The Holy Fire burned more than 23,000 acres across Orange and Riverside counties in 2018. Wanting to understand how the blaze affected bacteria and fungi over time, UCR mycologist Sydney Glassman led a team of researchers into the burn scar. “When we first came into fire territory, there was ash up to my shins. It was a very severe fire,” Glassman said.

The researchers visited the scar nine times over the course of the next year, comparing the charred earth with samples from nearby, unburned soil. Their findings, now published in the journal Molecular Ecology, show that the overall mass of microbes dropped between 50 and 80% after the fire, and did not recover during that first year. However, some things lived. 

UCR researcher sampling soil in the Holy Fire burn scar. Credit: Sydney Glassman/UCR.

It wasn’t just one type of bacteria or fungi that survived. Rather, it was a parade of microbes that took turns dominating the burned soil in that first post-fire year. “There were interesting, distinct shifts in the microbes over time. As one species went down, another came up,” Glassman said.

Certain microbes called methanotrophs regulate the breakdown of methane, a greenhouse gas. Fabiola Pulido-Chavez, UCR plant pathology Ph.D. candidate and first author of the study, noticed that genes involved in methane metabolism doubled in post-fire microbes. “This exciting finding suggests post-fire microbes can “eat” methane to gain carbon and energy, and can potentially help us reduce greenhouses gases,” Pulido-Chavez said.

What the researchers saw in the soil bears some resemblance to the human body’s response to a major stress. What is now being learned about post-fire microbe behavior could change older theories about plant behavior, since microbes were not factored into them. “To me, this is exciting, as microbes have long been overlooked, yet they are essential for ecosystem health,” Pulido-Chavez said.

One open question that remains is whether adaptations that plants and microbes have developed in response to wildfires will adapt again to megafires or recurrent fires. Whereas there might have been a period of several decades before a plot of land burned more than once, it is increasingly common for the same soil to burn again in fewer than 10 years.

Food & Agriculture Soil and Fertilizer

Ecological Intensification

Farming and fertilizers: how ecological practices can make a difference: Agriculture involves a difficult balance between food production and environmental impact. For example, fertilizers can help to achieve good crop yields, but over-using them produces greenhouse gas emissions and pollution. Some of these impacts also threaten future agricultural production. Greenhouse gas emissions, for instance, contribute to climate change and increase the likelihood of extreme weather events.

To sustain agriculture, then, it is necessary to minimize the use of inputs like fertilizers, and support crop growth in other ways. One approach is through increasing ecological functioning within farms. This means enhancing relationships between different on-farm organisms, including crops, livestock, microbes, and wild plants and animals. Using these relationships to support crop yields is called “ecological intensification”.

Previous research has shown that ecological intensification can be effective. But studies have only been done over short timescales of just a few years, whereas the effects of agricultural practices often take longer to become clear. Variation in weather between years can obscure effects in the short term, and some ecological processes take several years to stabilize.

In a recent study, my colleagues and I explored whether long-term studies also support ecological intensification. To answer this, we sought out 30 long-term experiments from around Europe and Africa. We used these experiments to look at whether ecological intensification could reduce the need for two inputs: nitrogen fertilizer and tillage. We found that ecological intensification can partly replace fertilizers to support crop yields, because both ecological intensification and fertilizers increase soil nutrients. So farmers could use ecological intensification to reduce fertilizer use while maintaining the same yields. Farmers who already used low or no fertilizer could increase their yields.