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)

Chemicals Climate Change Food & Agriculture

Hi-Tech Farming

This is the first in a series of three posts examining how we might adapt our food supply to the twin threats of climate change and peak oil. As much as I like to dream of world fed by small-scale regenerative agriculture, the reality is the Green Revolution largely solved world hunger. While the debate rages on about the limitations of the Green Revolution, there is no doubt that most plants benefit from fertilization and our commodified mono-crop agriculture depends on it.

Chart from Our World in Data.

The problem is that these fertilizers can also cause pollution and a lot of greenhouse gas emissions. Production of nitrogen-based fertilizers is a power-intensive process, and these fertilizers break down easily to produce nitrous oxide, which has roughly 300 times the warming potential of CO2.

Our agriculture depends on fertilizers. Image credits: James Baltz.

Can we make more sustainable fertilizers?

In an article by their CEO, Mihai Andrei, ZME Science recently explored whether we can make more sustainable fertilizers. Andrei explores the work of Paolo Gabrielli from ETH Zurich, who is looking at ways the chemical industry can achieve net-zero CO2 emissions. In a recent paper in the journal Environmental Research Letters, Gabrieilli quantifies the food and energy implications of transitioning nitrogen fertilizers to net-zero CO2 emissions. Together with colleague Lorenzo Rosa, Principal Investigator at Carnegie Institution for Science in Stanford, US, he set out to explore ways in which net-zero fertilizers could be produced. Among the strategies they suggest moving fertilizer production to countries with surplus renewable energy so as to reduce reliance on fossil fuels in the production stage. However, making fertilizer with electricity requires 25 times the amount of power that current techniques using natural gas require. A second pathway is to use carbon capture and sequestration technology to store carbon produced when making nitrogen-based fertilizers. However, this method requires a lot of new infrastructure and wouldn’t reduce our dependence on fossil fuels. The third pathway would be synthesizing hydrogen from biomass. Biomass requires a lot of arable land and water, often competing with agriculture, but it makes sense if the feedstock is waste biomass (crop residues). The hydrogen could be used for energy to produce new fertilizers. While none of these pathways is perfect, all are possible using today’s technology.

Credit: Patrick Ziegler / shutterstock

New food tech could release farmland back to nature

Researchers at University of York, UK, define the basic problem for conservation at a global level: food production, biodiversity and carbon storage in ecosystems are competing for the same land. Their assessment, conservation efforts are doomed to fail unless they address the underlying issue of food security. They see hope in new technologies that could release up to 80% of farmland from agriculture in the next century. Around four-fifths of the land used for human food production is allocated to meat and dairy, including both range lands and crops specifically grown to feed livestock. Add up the whole of India, South Africa, France and Spain and you have the amount of land devoted to crops that are then fed to livestock.

Beef and lamb might contain plenty of protein but they use vast amounts of land. Our World In Data (data: Poore & Nemecek (2018)), CC BY-SA

They propose cellular agriculture as an alternative. Sometimes called “lab-grown food”, the process involves growing animal products from real animal cells, rather than growing actual animals. Animal cruelty would be eliminated and, with no need for cows wandering around in fields, the factory would take up far less space to produce the same amount of meat or milk. Other emerging technologies include microbial protein production, where bacteria use energy derived from solar panels to convert carbon dioxide and nitrogen and other nutrients into carbohydrates and proteins. This could generate as much protein as soybeans but in just 7% of the area. The liberated land might be used for nature preserves, or to grow sustainable building materials. And the animal cruelty inherent in current meat production would be eliminated.

Longhorn cattle on a rewilding project in England: if we got most of our protein and carbs through new technologies, this sort of compassionate and wildlife-friendly farming could be scaled up. Chris Thomas, Author provided.

Cyanobacteria can help detoxify the environment on Mars. (NASA/Adam Arkin)

The food systems that will feed Mars are set to transform food on Earth

In Dinner on Mars, two Canadian scientists explore the technologies that might feed humans on Mars and how these might transform food production here on Earth. The basis of food systems on Mars would involve water harvested from the soil and cyanobacteria, which can use the carbon dioxide in the atmosphere and grow on the sandy inorganic and toxic regolith to produce the basic organic molecules on which the rest of the food system will rest. Cyanobacteria is capable of growing in Martian conditions, which has the very real added benefit of neutralizing extremely toxic chemicals called perchlorates. Perchlorates are laced throughout the Martian regolith and are toxic to humans in minute quantities, so having cyanobacteria provide a double duty of neutralizing the toxins while producing organic material will be a huge boon to any Martian community. Once bacteria are happily growing away under a Martian sky, they will provide nutrients needed to support luxurious crops of plants. Advanced greenhouse technologies — like vertical agriculture — that create a suitable controlled environment will provide abundant leafy greens, vegetables, fruits and specialty crops such as herbs, coffee and chocolate. Imagining what agriculture could be like on Mars is a fascinating project, but it’s when we think about how these technologies may affect life on Earth that this topic becomes extremely serious. The “waste” products of one part of the system need to be deliberately used as inputs into another part, such as using the dead cyanobacteria as a growth medium for later parts of the food system. But more than the technologies themselves, it may be the mindset of building a Martian food system that will change how things are done here on Earth, where one-third of all food is thrown away.

Across the globe, startups are testing robots to pollinate everything from blueberries to almonds. Illustration: Justin Metz. From the Wall Street Journal.

Robotic bees and roots

If you think Martian food systems are a stretch – think again! The EU is already funding research into Miniature robots that mimic living organisms are being developed to explore and support real-life ecosystems. (See also: ROBOtic Replicants for Optimizing the Yield by Augmenting Living Ecosystems).

Photo of roots that contain different dosages of a family of genes that affects root architecture, allowing wheat plants to grow longer roots and take in more water. Credit: Gilad Gabay / UC Davis

A key to drought-resistant wheat

Elsewhere intensive research aims to solve some of the challenges plants will face under a climate changed future. An international team of scientists found that the right number of copies of a specific group of genes can stimulate longer root growth, enabling wheat plants to pull water from deeper supplies. The resulting plants have more biomass and produce higher grain yield, according to a paper published in the journal Nature Communications.

This image shows the autonomous robot, with multiple tiers of PhenoStereo cameras, that are part of the AngleNet system. Credit: Lirong Xiang, NC State University.

Wheeled robots help breed better corn plants

All new technologies start with data collection. Researchers from North Carolina State University and Iowa State University have demonstrated an automated technology capable of accurately measuring the angle of leaves on corn plants in the field. This technology makes data collection on leaf angles significantly more efficient than conventional techniques, providing plant breeders with useful data more quickly. “The angle of a plant’s leaves, relative to its stem, is important because the leaf angle affects how efficient the plant is at performing photosynthesis,” says Lirong Xiang, first author of a paper on the work and an assistant professor of biological and agricultural engineering at NC State. “For example, in corn, you want leaves at the top that are relatively vertical, but leaves further down the stalk that are more horizontal. This allows the plant to harvest more sunlight. Researchers who focus on plant breeding monitor this sort of plant architecture, because it informs their work. The paper is published open access in the Journal of Field Robotics.

Concept of a decomposition sensor where the rate of erosion of a biodegradable conductive trace correlates with the microbial activity in the soil. Credit: Advanced Science (2022). DOI: 10.1002/advs.202205785

Biodegradable soil sensors

We end this post with a story about an elegant bit of research from the Paul M. Rady Department of Mechanical Engineering. Their biodegradable sensors may change the way farmers track, measure, and respond in real time to their soil’s microbial activity with big implications for addressing global greenhouse gas emissions. The work, recently published in Advanced Science, was led by Madhur Atreya and professors Greg Whiting and Jason Neff at CU Boulder. It describes how a cheap and easily printed sensor can measure soil health by tracking it’s own decomposition in real time—all with little to no impact on its outside environment and through the use of easily available electronics.