Tag Archives: soil science

U.S. topsoil

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A study published in Nature says the U.S. “corn belt” has lost something like 35% of its topsoil. Sounds concerning, and I have heard dramatic claims like “the world only has 50 years of topsoil left. I also just find it sad to think that the topsoil was built up by the prairies over the millennia, and we have mined much of it into oblivion in a few short industrial generations. But this article also puts the loss in terms of crop yields at around 6%, which doesn’t sound so dramatic. This makes me think we are relying largely on agricultural chemicals rather than nutrients in the soil itself. Maybe it would actually make more sense to intensify industrial agricultural in some areas or even indoors, contain the impacts, and restore some of those prairies.

a new dust bowl

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Sure, the U.S. has problems, and we are not doing a great job solving or even acknowledging all of them. Still, soil conservation is something we have had figured out since the 1920s, right? Not so fast, my friends. As we keep pushing for increased production, the amount of dust in the air (this is something we measure) keeps increasing. Warming and drying trends are not going to help.

This is Geophysical Research Letters.

Climate change and land use are altering the landscape of the U.S. Great Plains, producing increases in windblown dust. These increases are investigated by combining coarse mode aerosol observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor in addition to the Aerosol Robotic Network (AERONET) and Interagency Monitoring of Protected Visual Environments (IMPROVE) aerosol monitoring networks. Increasing trends of up to 5%/year in MODIS aerosol optical depth for dust observations are observed throughout the Great Plains (2000–2018). Cropland coverage has increased 5–10% over the majority of the Great Plains (2008–2018), and positive monthly trends in IMPROVE (1988–2018) and AERONET (1995–2018) coarse mode 90th percentile observations coincide with planting and harvesting seasons of predominant crops. Presently, results suggest increased dust due to agricultural expansion is negatively influencing human health and visibility in the Great Plains. Furthermore, results foreshadow a future where desertification becomes an increasing risk in the Great Plains.

Technosols

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A technosol is an artificially created planting/structural medium from manmade materials, such as construction debris and compost. This article from Ecological Engineering journal says a mix of 20% “excavated deep horizons” (in layman’s terms, I think this is just dirt from construction sites), 70% crushed concrete, and 10% compost might work. If we truly want green cities, and we don’t want to reduce natural habitats to wastelands by harvesting materials from them to green our cities, this could be a good approach.

November 2019 in Review

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Most frightening and/or depressing story:
  • The Darling, a major river system in Australia, has essentially dried up.
Most hopeful story: Most interesting story, that was not particularly frightening or hopeful, or perhaps was a mixture of both:

carbon sequestration potential of restoring degraded land

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The UN Convention to Combat Desertification says there is a large and potentially very cost-effective opportunity to sequester a lot of carbon by restoring degraded farmland. This is not planting trees or trying to green areas that were historically desert, but trying to restore areas that used to be productive cropland or grazing land to their original condition or better. It’s also an opportunity to expand food production without displacing productive natural ecosystems.

Rene Castro Salazar, an assistant director general at the UN Food and Agriculture Organization, said that of the 2 billion hectares (almost 5 billion acres) of land around the world that has been degraded by misuse, overgrazing, deforestation and other largely human factors, 900 million hectares could be restored.

Returning that land to pasture, food crops or trees would convert enough carbon into biomass to stabilize emissions of CO2, the biggest greenhouse gas, for 15-20 years, giving the world time to adopt carbon-neutral technologies…

Key to returning dry lands to vegetation is the use of fertilizer, said Mansur. “Fertilizers are essential for increasing productivity. Good fertilizer in the right quantity is very good for the soil.”

Time

ecosystem value of urban soil

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Soil is a critical part of a functional ecosystem, and yet most engineers and architects who work with soil in urban areas are not trained to really understand how soil works as part of an ecosystem. Soil scientists and agricultural engineers are, but they are not working in cities for the most part. Anyway, I like the premise of this article.

Towards an operational methodology to optimize ecosystem services provided by urban soils

Urban soils need to be taken into account by city managers to tackle the major urban environmental issues. As other soils in forest or agricultural environments, urban soils provide a wide range of ecosystem services. However, their contribution remains poorly assessed up to now, and as a result there is a strong lack of consideration by urban planning of the services they provide. Indeed, urban soils are mostly seen as a land surface (land area, two-dimensional system) and if they are characterized, it is almost exclusively for their potential contamination and their geotechnical properties. So, policy makers and planning operators rarely consider soils as a living resource, capable to fulfill essential functions. From the conclusions of previous studies, a selection of ecosystem services provided by soil and adapted to the specificity of urban context is proposed. This paper also aims at proposing the concept of the DESTISOL decision support system for urban planning projects upstream of the planning decisions, illustrated by an application example. It is based on an integrative approach linking soil quality indicators (e.g. physico-chemical and biological characteristics, fertility, pollution), soil functions and soil ecosystem services. The method leads to the semi-quantitative assessment of the level of ecosystem services that are either provided by urban soils or required to fit with the urban design.

restoring tropical peat swamps

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Restoring tropical peat swamps might not seem like such an important thing, until you realize the extent of clearing and burning that occurs in places like Indonesia each year. The amount of carbon emitted is staggering even in comparison to that of the economic activities of a major developed country like Japan.

A common-sense approach to tropical peat swamp forest restoration in Southeast Asia

Tropical peat swamp forests (TPSFs) are found mainly in Southeast Asia and especially Indonesia. A total of 61% were lost between 1990 and 2015 and 6% remained in a pristine condition by 2015. Tropical peat swamps store vast amounts of carbon in their peat, but peat degradation, through drainage and fire, leads to high greenhouse gas emissions. This is gaining much international attention and, with it, policy initiatives and funding for restoration from local to landscape scales are being promoted. Unfortunately, although there is a now strong desire and need for TPSF restoration, methods are lacking. Ecological understanding is still at an early stage, and, even more so, in its applied use. There is an imbalance between the activities of TPSF restoration and sound ecological application. Furthermore, while many activities are underway and knowledge is being gained, these techniques are yet to be published. This article has been written to provide a common-sense, practical guide to tropical peatland forest restoration which summarizes what we know to date, while acknowledging the gaps in our understanding. Topics covered include species selection, land assessment, land selection, and appropriate nursery, transplanting, and monitoring methods. The authors make no apologies that in places this reads like a manual as, given the importance of tropical peatland recovery and the recent attention and funding opportunities available, it is essential we now provide techniques to restoration practitioners working on the ground, and a basic common-sense approach must be the starting point.

I actually did my masters research on subtropical peat wetlands, so I know a little bit about this. Peat is formed by organic matter decomposing slowly under anaerobic conditions under shallow standing water for long periods of time. Bacteria and other biological processes that turn carbon into carbon dioxide operate slowly under anaerobic conditions, and new organic matter is able to build up faster than it can be broken down and liberated into the atmosphere. The same plants that decompose into peat grow in the decomposing remains of their predecessors, so that new layers get added gradually over time. When you drain the water, conditions in the soil become aerobic, and especially under warm conditions the organic matter gets mineralized (turned into carbon dioxide gas) faster than it can form. This happens even outside the tropics and in the absence of fire (the Everglades for example have seen a lot of soil loss), but catch the organic matter on fire and you get a triple threat – a smoky mess that is very bad for human health, habitat loss, and liberation of enormous amounts of carbon into the atmosphere. Do this on an enormous scale and it is truly a catastrophe. The world is not making a whole lot of progress in slowing this situation down, let alone stopping it, let alone beginning to restore what is being lost.

new book on soil

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Here’s a review on a new book on soil.

Soils had not excited many ecologists until, two decades ago, soil ecologists started emphasizing that many aboveground phenomena are under belowground control. Richard Bardgett is one of the most eloquent and knowledgeable of the soil scientists who have contributed to the current enthusiasm about soils. In his recent book Earth Matters: How Soil Underlies Civilization he explains how much human societies depend on soil. He writes about how soils are formed, how they influence biodiversity and food quality, and what role they play in cities and in war, and introduces us to the interplay of soils and climate change.

more on soil and carbon sequestration

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Here’s another article on soil management and carbon sequestration. Maybe the Rodale Institute is not completely unbiased, but there are serious scientific voices starting to say similar things.

Simply put, recent data from farming systems and pasture trials around the globe show that we could sequester more than 100% of current annual CO2 emissions with a switch to widely available and inexpensive organic management practices, which we term “regenerative organic agriculture.” These practices work to maximize carbon fixation while minimizing the loss of that carbon once returned to the soil, reversing the greenhouse effect.

soil and carbon sequestration

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This open-access article in Nature makes a surprising claim – that much better management of agricultural soil could offset a significant portion of annual carbon emissions from all sources (not just agriculture), while also being good for ecosystems and food security.

How important, in total, is this large, varied set of land-use and management practices as a GHG mitigation strategy? One of the challenges in answering this question is to distinguish between what is technically feasible and what might be achieved given economic, social and policy constraints. A comprehensive global analysis of agricultural practices combined climate-stratified modelling of emission reductions and soil C sequestration with economic and land-use change models to estimate mitigation potential as a function of varying ‘C prices’ (reflecting a social incentive to pay for mitigation). They estimated total soil GHG mitigation potential ranging from 5.3 Pg CO2(eq) yr−1 (without economic constraints) to 1.5 Pg CO2(eq) yr−1 at the lowest specified C price (US$20 per Mg of CO2(eq)). Average rates for the majority of management interventions are modest, <1 Mg CO2(eq) ha−1 yr−1. Thus, achieving large global GHG reductions requires a substantial proportion of the agricultural land base (Fig. 2). Although the economic and management constraints on biochar additions (not assessed by ref. 19) are less well known, ref. 67 estimated a global technical potential of 1–1.8 Pg CO2(eq) yr−1 (Fig. 2).

A more unconventional intervention that has been proposed is the development of crops with larger, deeper root systems, hence increasing plant C inputs and soil C sinks. Increasing root biomass and selecting for root architectures that store more C in soils has not previously been an objective for crop breeders, although most crops have sufficient genetic plasticity to alter root characteristics substantially and selection aimed at improved root adaptation to soil acidity, hypoxia and nutrient limitations could yield greater root C inputs as well as increased crop yields. Greater root C input is well recognized as a main reason for the higher soil C stocks maintained under perennial grasses compared to annual crops. Although there are no published estimates of the global C sink potential for ‘root enhancement’ of annual crop species, as a first-order estimate, a sustained increase in root C inputs might add ~1 Pg CO2(eq) yr−1 or more if applied over a large portion of global cropland area (Fig. 2).

Thus, the overall mitigation potential of existing (and potential future) soil management practices could be as high as ~8 Pg CO2(eq) yr−1. How much is achievable will depend heavily on the effectiveness of implementation strategies and socioeconomic and policy constraints.

I tried to get a quick answer on global annual emissions in Pg CO2(eq), and failed. Now I’m out of time. I’ll figure it out some other time.