Topsoil Depletion

[trm1958]

I tried searching for a topic on this and found only a few scattered references in other threads. Considering a large majority of our food comes, directly or indirectly, from topsoil, this seems a glaring omission to me.

Why soil is disappearing from farms
https://www.bbc.com/future/bespoke/follow-the-food/why-soil-is-disappearing-from-farms/

But beneath the feet of Iowa’s farmers, a crisis is unfolding. The average topsoil depth in Iowa decreased from around 14-18 inches (35-45cm) at the start of the 20th Century to 6-8 inches (15-20cm) by its end. Relentless tilling and disturbance from farm vehicles have allowed wind and water to whisk away this priceless resource.

What If the World’s Soil Runs Out?
https://world.time.com/2012/12/14/what-if-the-worlds-soil-runs-out/

A rough calculation of current rates of soil degradation suggests we have about 60 years of topsoil left. Some 40% of soil used for agriculture around the world is classed as either degraded or seriously degraded – the latter means that 70% of the topsoil, the layer allowing plants to grow, is gone. Because of various farming methods that strip the soil of carbon and make it less robust as well as weaker in nutrients, soil is being lost at between 10 and 40 times the rate at which it can be naturally replenished. Even the well-maintained farming land in Europe, which may look idyllic, is being lost at unsustainable rates.

New Evidence Shows Fertile Soil Gone From Midwestern Farms
https://www.npr.org/2021/02/24/967376880/new-evidence-shows-fertile-soil-gone-from-midwestern-farms

Thaler and his colleagues compared that color, as seen from satellites, with direct measurements of soil quality that the U.S. Department of Agriculture has carried out, and found that light brown soil contained so little organic carbon, it really wasn't A-horizon soil at all. The topsoil layer was gone. What's more, Thaler found that this was consistently the case on particular parts of the landscape. "The A-horizon was almost always gone on hilltops," he says.

Thaler believes that a century of plowing is to blame. The soil gradually fell down hillsides, a little bit each year, as farmers tilled the soil.

Thaler's team then expanded their study to fields of corn, soybeans, and other crops within a large area of the upper Midwest that includes much of Indiana, Illinois, Minnesota, and Iowa. They calculated that about a third of the crops were growing on erosion-prone hills. This produced their estimate that a third of all cropland in that region had lost its topsoil.

Rates of Historical Anthropogenic Soil Erosion in the Midwestern United States
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2021EF002396

1.  IntroductionConventional agricultural practices have accelerated soil erosion rates, resulting in widespread soil degradation throughout the world's agricultural regions (Montgomery, 2007b). Soil degradation diminishes soil fertility by removing organic matter and nutrients (Pimentel, 2006), which, without countervailing practices such as fertiliza-tion and genetic crop enhancements, leads to reductions in crop yields (Lal, 2004; Tilman et al., 2002). Fertilizer use,  however,  does  not  fully  restore  the  productivity  of  eroded  soils  (Fenton  et  al., 2005),  and  because  fossil  fuels are required to generate the energy required for fertilizer production, the use of fertilizers to increase yields in  degraded  soils  is  not  sustainable  (Montgomery, 2007a).  Further,  soil  erosion  leads  to  increased  agricultural  production costs (Pimentel et al., 1995) and negative offsite effects such as increased sedimentation and nutrient export to downstream waterbodies (Tilman et al., 2002). In the United States, recognition of the high costs of soil erosion in the early twentieth century led to the development and implementation of soil conservation practices (Bennett, 1948). Field trials have demonstrated the efficacy of soil conservation efforts (Pimentel et al., 1976; Steiner, 1987), but it is unclear whether the advent of soil conservation practices and policies has led to a reduc-tion of region-wide soil erosion rates in the U.S.Abstract  Erosion degrades soils, reduces crop yields, and diminishes ecosystem services. The total amount of soil that has been eroded since the initiation of farming is unknown in most agricultural landscapes, which hinders assessment of soil erosion trends. In the Midwestern U.S., erosion has caused native prairie remnants to become perched above surrounding farmland, providing an opportunity to measure historical soil erosion rates. We use high-resolution topographic surveys conducted across erosional escarpments at the boundary between 20 prairies and adjacent agricultural fields and show the median reduction in soil thickness ranges from 0.04 to 0.69 m, corresponding to erosion rates of 0.2–4.3 mm year −1, with a median value of 1.9 mm year −1. We used an association between the measured reduction in soil thickness and topographic curvature to predict regional soil erosion integrated since the beginning of farming to the present. We estimate a median historical erosion rate of 1.8 ± 1.2 mm year −1, which is nearly double the rate considered tolerable by the U.S. Department of Agriculture (USDA). Current soil loss predictions from the USDA National Resources Inventory (NRI) and the Daily Erosion Project (DEP) are lower than our historically averaged erosion rate by a factor of 3 and 8, respectively. We suggest that the NRI and the DEP underpredict soil loss rates because they do not include tillage erosion, a process shown to be important throughout the Midwestern U.S. Our findings indicate that further implementation of conservation practices is needed to reduce the high centennial-averaged soil erosion rates that we measure to sustainable levels

More than 57 billion tons of soil have eroded in the U.S. Midwest
https://www.sciencenews.org/article/soil-erosion-rate-us-midwest-unsustainable-usda

This corresponds to the loss of roughly 1.9 millimeters of soil per year from agricultural fields since the estimated start of traditional farming at these sites more than a century and a half ago, the researchers calculate. That rate is nearly double the maximum of one millimeter per year that the USDA considers sustainable for these locations. 

Why the global soil shortage threatens food, medicine and the climate
https://www.cnbc.com/2022/06/05/why-the-global-soil-shortage-threatens-food-medicine-and-the-climate.html

The United Nations declared soil finite and predicted catastrophic loss within 60 years.

“There are places that have already lost all of their topsoil,” Jo Handelsman, author of “A World Without Soil,” and a professor at the University of Wisconsin-Madison, told CNBC.

The impact of soil degradation could total $23 trillion in losses of food, ecosystem services and income worldwide by 2050, according to the United Nations Convention to Combat Desertification.

[kassy]

We need to change how we think about soil, says new research


With the UK reaching record temperatures this summer along with the driest conditions since 1976, ongoing concerns about food security, wildlife habitats and biodiversity, having a healthy soil system is more vital and challenging than ever before. But what does the term ‘soil health’ mean and how should we measure it? New research from Cranfield and Nottingham Universities says that how we think about, measure and study soil must be changed to give a better understanding of how to manage this resource effectively, with academics proposing an entirely new approach for assessing soil health.

Jim Harris, Professor of Environmental Technology at Cranfield University, led the research and says: “Although ‘soil health’ as a term is quite widely used now, it is problematic as it means different things to different people, and there is no single agreed way to measure the overall health of this system.

“Through this research, we want to start the conversation about how we move to a holistic picture of soil health assessment, looking at the interconnected elements of this universally important system. Taking steps towards a bigger-picture view of soil health could help make a huge difference to some of our big challenges, not least the climate crisis.”

Range of measures will help assess direction of travel

Current approaches measure individual soil properties and use these to try and assign a single number giving an overall soil health ‘score’, but the researchers argue that this does not reflect the wider system perspective that’s needed to fully assess the condition of a soil and its health over time.

Dr Dan Evans, a 75th Anniversary Research Fellow at Cranfield University who co-authored the paper commented: “Just as we don’t have a single measure or score for human health, because this can’t reflect the complexities of the whole body, we should not rely on a single score for soil health. Taking in a range of measures to look at the whole system will mean we can fully understand the direction of travel – is soil getting better, or worse?”

Whole system approach measures four key areas

The researchers propose a whole system approach to assess soil health, based on a new hierarchical framework which takes in several measures:

Signs of Life – characterising the organisms existing in soil
Signs of Function – the extent to which soils process materials
Signs of Complexity - the extent to which soil components are connected and interdependent
Signs of Emergence – the extent to which soils respond and recover to multiple stressors
Sacha Mooney, Professor in Soil Physics at the University of Nottingham added, “This new approach can be applied to all soils and moves us closer to an interdisciplinary understanding of the ‘whole picture’ of the soil system, rather than separately considering the individual pieces of the jigsaw.”

Professor Harris continued: “It is hard to understate the importance of having a healthy soil system – it supports wildlife and biodiversity, reduces flood risks, stores carbon and gives us food security. Moving towards this new model of assessment is going to help land users and governments to sustainably manage our global soil resources for future generations.”

The research paper A new theory for soil health is published by the European Journal of Soil Science and was written by Professor J.A.Harris, Dr D.L.Evans and Professor S.J.Mooney of the University of Nottingham.

https://www.eurekalert.org/news-releases/960594

OA paper:

A new theory for soil health

Abstract
The term ‘soil health’ has captured the interest of government, and land managers, whilst the academic community has struggled to rationalise its use and wider benefit. It has proved a powerful tool in conveying best practice to a lay audience. However, the widespread adoption of the ‘metaphor’ has resulted in calls for tools that facilitate the measurement of soil health, preferably quantitatively, and often as a single figure, for ease of use/communication and cost of monitoring. The insurmountable problem is that soil health is neither a readily quantifiable nor measurable object. Only organisms can have ‘health’, which manifests as characteristics of a living system - true of complex systems exhibiting ‘emergent’ properties such as resilience in the face of perturbation.

We pose the key question: is soil really a system capable of exhibiting ‘health’, or any other property emerging from a complex, connected, self-regulating system? We argue that if you cannot detect emergent properties, you are: i) looking at the wrong dynamic parameter; ii) not considering the entire system; or iii) not evaluating at a system at all. We suggest that our focus should instead be on the relationships between components, complexity, and function.

Using this as a basis for a new framework will allow us to assemble and align disparate threads of soil science into a cogent and coherent ‘new theory of soil health’, which is an essential and practical step forward for the sustainable management of global soil resources, across all land uses.

https://bsssjournals.onlinelibrary.wiley.com/doi/10.1111/ejss.13292

[johnm33]

A new theory for soil health

Mostly from links here I've come to the view that soil health is largely dependent on having a variety of grazers together and consecutively refining the bacteria present as fodder passes through them and back into the soil, this in turn keeps them [and us] healthy.

[El Cid]

that might be true for steppe environments but definitely not for forests which (would) make up the majority of the natural landscape...also, soil health can be improved very much without animals, simply by planting trees (eg agroforestry)

[kassy]

Solutions vary according to where you are and to and extent by what you are trying to do or which landscape you actually manage.

[Bruce Steele]

“Signs of Life – characterising the organisms existing in soil
Signs of Function – the extent to which soils process materials
Signs of Complexity - the extent to which soil components are connected and interdependent
Signs of Emergence – the extent to which soils respond and recover to multiple stressors
Sacha Mooney, Professor in Soil Physics at the University of Nottingham added, “This new approach can be applied to all soils and moves us closer to an interdisciplinary understanding of the ‘whole picture’ of the soil system, rather than separately considering the individual pieces of the jigsaw.”

Soil processes are different in different environments, tropical forest, temperate forest, savanna, tundra, or desert. Above list would seem like a better way to define what we are looking for when we talk about soil health. I might add something like Function as a carbon sink -

[kassy]

That should come out of the other processes.

No life, no sink.
Function...well depends on local stressors currently active and the Complexity and Emergence are higher order processes. If you have 10 years of good function it might build if you have 10 years of drought stress interspersed with flash floods then it might erode.

[Bruce Steele]

Kassy, There are some inorganic processes that can be enhanced  with certain types of rock dust applications. Energy costs of mining , crushing and distributing rock dust means it is only effective when farm fields are close to mineral sources.

[kassy]

Unearthing the impact of moisture on soil carbon processes


The ground below your feet contains some 2,500 gigatons of carbon, approximately three times the amount of carbon held in our atmosphere and four times more than is stored in every living thing -- trees, ants, whales, and humans included -- on our planet.

Despite this, the dynamics that drive soil carbon cycles are less understood than the dynamics of other carbon stocks.

Now, researchers from across Virginia Tech, in collaboration with scientists with the U.S. Department of Agriculture's Forest Service, the National Science Foundation's National Ecological Observatory Network (NEON), and other universities, are offering a new perspective on those processes, revealing that moisture is a critical driver in the regulation and sequestration of soil carbon stocks.

"We're demonstrating, at the molecular level, that there is a big split in how carbon in soil is cycled between humid and arid soil systems," said Brian Strahm, a professor in the College of Natural Resources and Environment's Department of Forest Resources and Environmental Conservation and a primary investigator on the grant that funded this research. "This is useful in allowing us to imagine two fundamentally different models of how carbon is concentrated and moves within soil."

...

https://www.sciencedaily.com/releases/2023/02/230208124214.htm


Moisture-driven divergence in mineral-associated soil carbon persistence
https://www.pnas.org/doi/10.1073/pnas.2210044120


Abstract
Mineral stabilization of soil organic matter is an important regulator of the global carbon (C) cycle. However, the vulnerability of mineral-stabilized organic matter (OM) to climate change is currently unknown. We examined soil profiles from 34 sites across the conterminous USA to investigate how the abundance and persistence of mineral-associated organic C varied with climate at the continental scale. Using a novel combination of radiocarbon and molecular composition measurements, we show that the relationship between the abundance and persistence of mineral-associated organic matter (MAOM) appears to be driven by moisture availability. In wetter climates where precipitation exceeds evapotranspiration, excess moisture leads to deeper and more prolonged periods of wetness, creating conditions which favor greater root abundance and also allow for greater diffusion and interaction of inputs with MAOM. In these humid soils, mineral-associated soil organic C concentration and persistence are strongly linked, whereas this relationship is absent in drier climates. In arid soils, root abundance is lower, and interaction of inputs with mineral surfaces is limited by shallower and briefer periods of moisture, resulting in a disconnect between concentration and persistence. Data suggest a tipping point in the cycling of mineral-associated C at a climate threshold where precipitation equals evaporation. As climate patterns shift, our findings emphasize that divergence in the mechanisms of OM persistence associated with historical climate legacies need to be considered in process-based models.

[Bruce Steele]

Kassy, Almost every year I put out a cover crop to try and improve soil carbon, tilth ,and water retention. In sandy soil that annually dries out it always seems like a losing battle.
 Oak forest canopy with associated lichen can fix nitrogen and contribute to healthy soils. Only problem is people far prefer vegetables to acorns.

https://www.fs.usda.gov/psw/publications/documents/psw_gtr160/psw_gtr160_04_knops.pdf

[zenith]

that may be one of the reasons why many nomadic (semi-nomadic) cultures would plant small plots distributed throughout the forest.

[Human Habitat Index]

Permaculture is the solution.

[Bruce Steele]

Acorns can provide carbohydrates in a nomadic culture, it would still work and nobody will miss a few acorns that go missing. 
 I just wanted to point out that arid regions can sink carbon IMO in oak habitat. However thousands of acres of oak Forrest have gone under the plow. It would take a lot of work to just get back the carbon sink that used to exist.

[zenith]

i'm talking about peoples that clear small areas and plant specific crops, they would keep them small and distributed. the next time they visited the site the forest would have taken over and they'd rinse and repeat.

alternatively the first nations here would burn the gary oak grove floors to encourage camas plants to grow as the bulbs were their main source of starch.

both relatively low impact and didn't require total human management.

edit - i've seen the first technique in numerous documentaries about indigenous peoples in tropical rainforests. even smaller plots/fields, hedgerows and forests were more typical in the uk/europe but they don't lend themselves to modern monoculture industrial farming.

[kassy]

Kassy, Almost every year I put out a cover crop to try and improve soil carbon, tilth ,and water retention. In sandy soil that annually dries out it always seems like a losing battle.

It might be. In combination with the non cover crop it might still lose carbon.

[morganism]

slightly OT)

Hell on Earth. How Russian aggression is devastating Ukrainian black soil
(...)
Ukrainian soils are a real treasure. Although Ukraine occupies less than 0.5% of the world's total land area, it has about 6-8% of its black soil reserves. This soil is the major contributor to Ukraine's position as one of the world's agricultural leaders.
(snip)
The soil from a shell crater in a schoolyard in Mykolaiv Oblast appeared to contain over 600 milligrams of lead per kilogram. This is about 20 times the maximum permissible concentration (MPC), the threshold amount considered safe for human health.

A kilogram of soil near the crater contains only 25 milligrams of lead. This is less than the MPC, and it proves there were no lead concerns in the ground before the shell exploded in the schoolyard. Testing this is also important, as military operations often occur in industrial zones, where the environment was far from exemplary even before the war.
Another sample taken by Kateryna at the site of a missile crater in the forest, located in Mykolaiv Oblast, contained copper concentrations exceeding normal levels by over a hundred times.

Such high concentrations of hazardous metals are not common at the site of hostilities. However, for mercury, vanadium and cadmium, exceeding background values by a factor of 3-6 is commonplace.

Deadland

Heavy metals are far from the only chemical trace of warfare in the soil. Explosions, spills and combustion release a whole bunch of different chemical compounds into the environment, from practically safe ones, such as carbon dioxide, to obviously harmful ones. For example, trinitrotoluene, also known as TNT, is toxic to humans and soil organisms.

All of these "chemical weapons" in high concentrations, combined with the high temperature and pressure from the explosion, can literally kill the soil.

Liudmyla Biliavska conducted experiments involving different soil samples from the battlefield to test whether it was suitable for growing plants. It turned out that wheat seeds do not germinate in the soil from under a burnt-out tank.

It could be even worse if some plants sprout on the war-torn land.

How to deal with craters?

The type and amount of chemical pollutants that get deposited in the ground during hostilities can vary. It depends – among other things – on the type of substance used, the type of soil, and what grows in the area.

Some substances might end up in ground waters that might be used or consumed by humans. Others might end up in agricultural plants – and from there, make their way into human bodies.

Leafy greens, for example, are particularly prone to accumulating heavy metals.

That is why Kateryna Polianska insists that covering up a crater in a field or on a vegetable patch with fresh ground and continuing to grow vegetables and other agricultural products on that spot is far from an ideal solution. Ideally, damaged soil has to be dug up and replaced with fresh, "healthy" soil.

But there are no designated areas in Ukraine where the soil damaged in shelling could be safely stored. Moreover, there isn’t an easily accessible supply of "healthy" soil to treat all craters left after shells and projectiles.

In light of this, environmentalist Oleksii Vasyliuk’s proposal for Ukraine to temporarily use Russian fields doesn’t seem all that far-fetched. Though it doesn’t appear particularly realistic, either.
(more)

https://www.pravda.com.ua/eng/articles/2023/08/13/7415256/