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.


Plants in History

One of my favorite categories of garden-related science stories is one I call “eye-candy, oddities & miscellany”. It includes articles that celebrate the beauty of nature and our gardens, stories that make me say “wow” – sometimes out loud, and reports of general weirdness. I last posted something on this category in mid-January. Since then, I’ve accumulated so many such stories that I’m breaking the category into three. Let’s start with historical notes relating to plants.

A 2000-year old loaf of bread. Image courtesy of Museo Archeologico Nazionale di Napoli.

2000-Year old Roman bread recipe

While many occupied their COVID lockdown time learning to bake bread, how about a truly historical recipe? Mihai Andrei, editor in chief at ZME Science shares a sourdough recipe from Pompei and how it came to be rediscovered thanks to archaeology and chemistry research.

Close-up of carving on wood, Patrai, Greece (De Agostini via Getty Images)

Drinking culture

In Salon, staff writer Troy Farah interviews UBC philosophy professor Edward Slingerland about his provocative theory and the book it inspired. In his 2021 book, “Drunk: How We Sipped, Danced, and Stumbled Our Way to Civilization,” Slingerland lays out the case that alcohol may have even been the impetus for humans developing agriculture and complex societies. Slingerland found evidence that, as he writes, “various forms of alcohol were not merely a by-product of the invention of agriculture, but actually a motivation for it — that the first farmers were driven by a desire for beer, not bread.”

When asked for examples, Slingerland notes the following. “When I started doing the research, I encountered this movement in archaeology that I think is gaining adherence and seems quite plausible. That’s called the Beer Before Bread hypothesis. So 13,000 years ago or so, we’re coming together, building these monumental religious sites and feasting. And feasting involved eating meat and other kind of high value items, but also drinking beer. Sites like Gobekli Tepe, [the world’s oldest surviving permanent human settlement], we don’t have direct chemical evidence, but we have these big vats. They were drinking some kind of liquid. And we know from other sites in the area, they were making beer at this time. In some cases beer, probably laced with psychedelics. So in that respect, the desire to get intoxicated actually directly led to civilization. It’s what motivated hunter gatherers to start cultivating crops and settling down. And you see this pattern around the world, not just in the Fertile Crescent but also Mideast, which is now the modern Turkey area, where agriculture first got started.”

Heriot-Watt’s International Centre for Brewing and Distilling is using 200-year-old barley in a project with Holyrood Distillery in Edinburgh. Credit: Holyrood Distillery

200-year-old barley for modern whisky

Heriot-Watt University’s Dr Calum Holmes is working to develop new whiskeys using old strains of barley. Experts from Heriot-Watt’s International Centre for Brewing and Distilling (ICBD) are working with Holyrood Distillery in Edinburgh to find out whether old species of barley could create distinctive new whiskies. Over the next six years, they’ll test at least eight heritage barley varieties and provide the scientific evidence needed to classify the flavours and aromas they bring to a dram. “There’s hope that using these heritage varieties of barley might allow for recovery of favourable aroma characteristics.”, says Dr. Holmes. 200-year-old Chevallier is one of the varieties they’ll be distilling. It was the most popular barley in Britain for 100 years but fell out of favour when tax rules changed. They’ll also test Hana, which was originally grown in Czech Moravia and was used to make the first blond Pilsner lager in 1842. Golden Promise is from the 1960s and grows predominantly on the east coast of Britain, from Angus down to Northumberland. It is best known as the barely behind the iconic Macallan bottlings from the sixties. The team hopes that the research will create new single malts for Holyrood Distillery and increase knowledge and awareness about the positive traits of heritage barleys. 

“The Houses of Parliament, Sunset,” by Claude Monet (1913). Image credit: Active Museum/Active Art/Alamy Stock Photo.

Hazy impressionist landscapes

Impressionist artists like Claude Monet and Joseph Mallord William (J. M. W.) Turner are famous for their hazy, dreamlike paintings. However, a new study finds that what these European painters were really depicting in their works wasn’t a figment of their imagination, but an environmental disaster: air pollution. Scientists examined approximately 100 artworks by the two impressionist painters, who dominated the art scene between the mid-18th and early 20th centuries, during the Industrial Revolution. The team discovered that what some art enthusiasts had long believed was Monet and Turner’s style of painting was actually them “capturing changes in the optical environment” that were associated with a decrease in air quality as coal-burning factories began dotting European cities and spewing pollutants into the air, according to the study, published in the journal Proceedings of the National Academy of Sciences.

The son of study first author Zhuo Feng, of Yunnan University in Kunming, China collecting a leaf of Bauhinia that shows signs of symmetrical insect-feeding damage. Image credit: Zhuo Feng (CC BY-SA).

Plants ‘slept’ with curled leaves 250 million years ago

Each night at sunset, a handful of plants “fall asleep.” Species as diverse as legumes and daisies curl up their leaves and petals for the evening and do not unfurl until morning. Now, a new study suggests that plants may have been folding their leaves at night for more than 250 million years. By tracking the unique bite marks that insects inflict only upon folded leaves, the authors determined that one extinct group of plants were likely nyctinastic — the scientific term for plants curling up in response to darkness.

Evidence of insect feeding damage on the leaf of the now extinct Gigantopterid. Image credit: Current Biology/Feng et al. (CC BY-SA).

“Since it is impossible to tell whether a folded leaf found in the fossil record was closed because it experienced sleeping behavior or because it shriveled and bent after death, we looked for insect damage patterns that are unique to plants with nyctinastic behavior,” study co-author Stephen McLoughlin, curator of Paleozoic and Mesozoic plants fossil collections at the Swedish Museum of Natural History in Stockholm, said in a statement(opens in new tab). “We found one group of fossil plants that reveals a very ancient origin for this behavioral strategy.”

After examining hundreds of specimens and photographs of gigantopterid fossils, the authors discovered symmetrical holes indicating that the leaves of these prehistoric plants were mature and folded when they were bitten. The results, published in the journal Current Biology, provide the strongest evidence to date of nyctinasty in ancient plant species.

Indigenous Knowledge Trees & Forests

2023 February Indigenous Plant Wisdom

Image from BC Greenhouse Builders.

An Indigenous reservation has a novel way to grow food – below the earth’s surface

A fascinating article by Hallie Golden highlights how members of the Oglala Sioux Tribe in South Dakota are improving food security and community resilience in the face of climate change. Underground greenhouses, called walipini are helping the people to take back control of their nutrition and ease farming amid the climate crisis, which has seen floods, high winds and hailstorms destroy outdoor crops and regular greenhouses. See also, this earlier article from the BBC about similar technologies being used in Bolivia: Farming underground in a fight against climate change.

A new study led by SMU suggests “cultural burning” could potentially weaken the role of climate in triggering today’s wildfires. Credit: Chris Guiterman

For 400 years, Indigenous tribes buffered climate’s impact on wildfires in the American Southwest

Adding to a growing body of evidence, new research from Southern Methodist University suggests bringing “good fire” back to the U.S. and other wildfire fire-prone areas, as Native Americans once did, could potentially blunt the role of climate in triggering today’s wildfires. The age-old Native American tradition of “cultural burning” appears to have previously weakened—though not entirely eliminated—the link between climate conditions and fire activity for roughly 400 years in the southwestern United States. Studying a network of 4,824 fire-scarred trees in Arizona and New Mexico, where the Apache, Navajo and Jemez tribes lived, SMU fire anthropologist Christopher Roos and other researchers found that the typical climate-fire pattern from 1500 to 1900 reflected one to three years of above-average rainfall—allowing vegetation to grow—followed by a fire-fueling year of significant drought. But the pattern was broken when Native American tribes performed traditional burning practices, according to the group’s study published in Science Advances.

See also:

Credit: Unsplash/CC0 Public Domain

Forests in protected Indigenous lands are healthier, scientists find

Over the last two centuries, human actions have resulted in rising temperatures, a massive carbon imbalance, and tremendous biodiversity loss. However, there are cases in which human stewardship seems to help remediate this damage. Researchers publishing in the journal Current Biology examined tropical forests across Asia, Africa and the Americas and found that the forests located on protected Indigenous lands were the healthiest, highest functioning, most diverse, and most ecologically resilient. Understanding how Indigenous management leads to better outcomes is key to a more equitable approach to conservation. Sze hopes that she and her colleagues can continue to understand how Indigenous land rights and management fit into our conservation policy. “My research is very much inspired by what decolonial climate movements are trying to achieve, in trying to have Indigenous communities and local communities have more autonomy over these spaces,” she says.

Arborist Steve Houser examines the California Crossing tree, a pecan with a bent trunk that points to a low-water crossing in Dallas. Photo by: Michael Amador.

If These Trees Could Talk

No historical marker indicates that this particular pecan tree near the grounds of the Texas National Guard Armory in northwest Dallas is special—just the fact that its trunk grows along the ground for about 25 feet before turning upward. Sometimes natural forces, such as ice storms, can bend trees into strange shapes like this. But for this pecan, its shape is no accident. Steve Houser, a local arborist and founding member of the Texas Historic Tree Coalition, traces his fingers over scars on the tree’s trunk, signs indicating humans may have lashed down the trunk with yucca rope some 150 years ago, when it was a flexible sapling. The bent tree, known as the California Crossing marker tree, points to a low-water crossing on the Elm Fork of the Trinity River, offering valuable information to those who would have recognized it as a marker tree. “The typical settler would go right by,” says Houser, chairman of the coalition’s Indian Marker Tree Committee. “A Comanche would see it and follow it. Trees told them where to go to.” He has been studying marker trees for more than 20 years and last year released a book on the topic, Comanche Marker Trees of Texas, co-authored with Jimmy W. Arterberry, the Comanche Nation tribal administrator, and Linda Pelon, a Waco anthropologist. With the extra publicity of the book, members of the public have come forward with many more posibilities. Houser now has a list of 176 potential marker trees. The article goes on to note that marker trees must be at least 150 years old, are usually long-lived native species, like bur oaks or pecans, and may be scarred where they were deliberately altered or tied down. The presence of arrowheads near the trees can help to bolster the case.