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trm1958

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Topsoil Depletion
« on: July 22, 2022, 02:15:50 PM »
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/
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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/
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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
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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
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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
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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
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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

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Re: Topsoil Depletion
« Reply #1 on: August 03, 2022, 11:06:34 AM »
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
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johnm33

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Re: Topsoil Depletion
« Reply #2 on: August 03, 2022, 08:03:48 PM »
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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

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Re: Topsoil Depletion
« Reply #3 on: August 03, 2022, 08:19:27 PM »
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

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Re: Topsoil Depletion
« Reply #4 on: August 03, 2022, 08:39:52 PM »
Solutions vary according to where you are and to and extent by what you are trying to do or which landscape you actually manage.
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Bruce Steele

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Re: Topsoil Depletion
« Reply #5 on: August 03, 2022, 08:50:37 PM »
“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

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Re: Topsoil Depletion
« Reply #6 on: August 03, 2022, 09:12:41 PM »
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.

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Bruce Steele

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Re: Topsoil Depletion
« Reply #7 on: August 03, 2022, 11:05:37 PM »
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.