Dietary shifts driving up phosphorus use

Seed Daily via SPX: Dietary changes since the early 1960s have fueled a sharp increase in the amount of mined phosphorus used to produce the food consumed by the average person over the course of a year, according to a new study led by researchers at McGill University. Between 1961 and 2007, rising meat consumption and total calorie intake underpinned a 38% increase in the world's per capita "phosphorus footprint," the researchers conclude in a paper published online in Environmental Research Letters.

The findings underscore a significant challenge to efforts to sustainably manage the supply of mined phosphorus, a non-renewable resource widely used as fertilizer.

When phosphorus is lost through agricultural runoff or sewage systems, it can pollute waterways downstream. In addition, because deposits are heavily concentrated in a few countries, global supplies and prices for the resource are vulnerable to geopolitical tensions.

In recent years, many researchers have explored how human activity has altered the phosphorus cycle in the environment and how management of phosphorus could be altered to ensure long-term sustainability. This new study sheds more light, in particular, on how diet choices have affected the intensity of phosphorus use around the world.

"Our results demonstrate that changes in diet can be a significant part of the strategy for enhancing sustainability of phosphorus management," says lead author Genevieve Metson, a doctoral student in McGill's Department of Natural Resource Sciences. "In particular, reduced consumption of meat, and especially beef, in countries with large phosphorus footprints could put a big dent in demand for mined phosphorus - since it takes many kilograms of feed, which is fertilized, to produce a kilogram of meat."....

Illustration from Brockhaus and Efron Encyclopedic Dictionary (1890—1907)

Amazon deforestation brings loss of microbial communities

EurekAlert via the University of Massachusetts at Amherst: An international team of microbiologists led by Klaus Nüsslein of the University of Massachusetts Amherst has found that a troubling net loss in diversity among the microbial organisms responsible for a functioning ecosystem is accompanying deforestation in the Amazon rainforest.

Nüsslein, an expert in tropical rain forest microbial soil communities, says, "We found that after rainforest conversion to agricultural pastures, bacterial communities were significantly different from those of forest soils. Not only did the pasture soils show increased species numbers, these species were also less related to one another than in rainforest soil. This is important because the combination of lost forest species and the homogenization of pasture communities together signal that this ecosystem is now a lot less capable of dealing with additional outside stress."

He and colleagues studied a large farm site over the past four years at the frontier where farmers drive agriculture into pristine rainforest in Rondonia, Brazil, to convert rainforest to agricultural use. Findings in part validated previous research showing that bacteria in the soil became more diverse after conversion to pasture. However, in its fourth year, their study overcame limitations of earlier investigations to show that changes in microbial diversity occurred over larger geographic scales. Results appear in the current issue of Proceedings of the National Academy of Sciences.

In addition to Nüsslein at UMass Amherst, the research group includes first author Jorge Rodrigues at the University of Texas at Arlington with Brendan Bohannan at the University of Oregon, James Tiedje at Michigan State University, and others at the University of Sao Paulo. Lead investigators Nüsslein and Rodrigues emphasize that the study is an equal collaboration among the four research groups.

Findings do not support earlier study conclusions, instead they show that the loss of restricted ranges for different bacteria communities results in a biotic homogenization and net loss of diversity overall. Scientists worry that the loss of genetic variation in bacteria across a converted forest could reduce ecosystem resilience. The researchers hope their work will provide valuable data to those making decisions about the future of the Amazon rainforest....

From NASA: The 38-kilometer-long Lago do Erepecu (Lake Erepecu) in Brazil runs parallel to the lower Rio Trombetas (Trombetas River), which snakes along the upper half of this astronaut photograph. Water-bodies in the Amazon Rainforest are often so dark they can be difficult to distinguish. In this image, however, the lake and river stand out from the uniform green of the forest in great detail as a result of sun-glint on the water surface. Sun-glint is the mirror-like reflection of sunlight off of a surface directly back towards the viewer, in this case an astronaut on-board the International Space Station. Forest soil is red, as shown by airfield clearings near Porto Trombetas (image far upper left), a river port on the south side of the Trombetas River.

Soil determines fate of phosphorus

Brown University News: Just 20 years ago, the soils of the Amazon basin were thought unsuitable for large-scale agriculture, but then industrial agriculture — and the ability to fertilize on a massive scale — came to the Amazon. What were once the poorest soils in the world now produce crops at a rate that rivals that of global breadbaskets. Soils no longer seem to be the driver — or the limiter — of agricultural productivity. But a new Brown University-led study of three soybean growing regions, including Brazil, finds that soils have taken on a new role: mediating the environmental consequences of modern farming.

The study focuses on the relationship between soils and phosphorus, a key agricultural nutrient. Typically in short supply, particularly in tropical soils, phosphorus is unique among fertilizer requirements. It is finite, irreplaceable and mined in just a few places around the world.

“If that suggests scarcity, which is a concern, the overuse of phosphorus can also pose another problem, causing harmful algal blooms in waterways,” said Stephen Porder, assistant professor of biology in the Department of Ecology and Evolutionary Biology and co-author of the study in the January 2013 edition of BioScience, posted early online. “It’s a bit of a Goldilocks problem — too much and our waterways are choked with algae, too little and we cannot produce enough food.”

...The new study compares the production of a single crop, soybeans, in the three places they are grown most — Iowa in the United States, Mato Grosso in Brazil, and Buenos Aires in Argentina. What the authors found was an example that illustrates how the combination of management and soil type frames the phosphorus-related concerns associated with these massive agricultural enterprises.

“Here are three regions where the crop that comes off the farm field is the same, but the fertilizer that goes in and the effects of this fertilizer on the environment are very different,” said lead author Shelby Riskin of Brown University and the Marine Biological Laboratory.

 “Having a one-size-fits-all approach to our understanding of interaction between people and their environment via agriculture is going to lead us to some erroneous concerns and conclusions if we don’t take the regional biophysical setting into account,” Porder said. “If you are concerned about the global phosphorus supply, Brazil is your problem — they are using a ton of it. If you are concerned about lakes and rivers being filled with algae, then Iowa is your problem, and learning how to mitigate even very small amounts of loss after decades of overfertilization is a real challenge.”...

Harvesting cotton in Brazil, shot by João Felipe C.S, public domain

Invasive plant species may harm native grasslands by changing soil composition

Newswise: The future landscape of the American Midwest could look a lot like the past—covered in native grasslands rather than agricultural crops. This is not a return to the past, however, but a future that could depend on grasslands for biofuels, grazing systems, carbon sequestration, and other ecosystem services. A major threat to this ecosystem is an old one—weeds and their influence on the soil.

According to a study in the journal Invasive Plant Science and Management, when invasive plants spread, they can leave behind a “legacy” of alteration in the native soil. Even after an invading species has been controlled, its effects can inhibit the regrowth of native plant species. The causes of this process are still being investigated and may involve changes in soil food webs, soil microbial communities, and mutualistic fungi.

In the study, researchers tested soil conditions for changes in composition after three growth cycles of invasive plant species. Researchers looked for changes in colonization rates, diversity, and composition of arbuscular-mycorrhizal fungi (AMF).

Three exotic plant species—crested wheatgrass, smooth brome, and leafy spurge—were tested in a glasshouse experiment. These plants, all characterized as strong invaders, were grown in native soil collected from North Dakota grasslands. Native species, including western wheatgrass, little bluestem, and blue gramma, were also grown, and after three growth cycles, soil composition was compared among these treatments....

Grasslands in Inner Mongolia, shot by Shizhao, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Fertile soil doesn't fall from the sky: The contribution of bacterial remnants to soil fertility has been underestimated until now

Helmholtz Centre for Environmental Research: Remains of dead bacteria have far greater meaning for soils than previously assumed. Around 40 per cent of the microbial biomass is converted to organic soil components, write researchers from the Helmholtz Centre for Environmental Research (UFZ), the Technische Universität Dresden (Technical University of Dresden) , the University of Stockholm, the Max-Planck-Institut für Entwicklungsbiologie (Max Planck Institute for Developmental Biology) and the Leibniz-Universität Hannover (Leibniz University Hannover) in the professional journal Biogeochemistry.

Until now It was assumed that the organic components of the soil were comprised mostly of decomposed plant material which is directly converted to humic substances. In a laboratory experiment and in field testing the researchers have now refuted this thesis. Evidently the easily biologically degradable plant material is initially converted to microbial biomass which then provides the source material to soil organic matter.

Soil organic matter represent the largest fraction of terrestrially bound carbon in the biosphere. The compounds therefore play an important role not only for soil fertility and agricultural yields. They are also one of the key factors controlling the concentration of carbon dioxide in the atmosphere. Climatic change can therefore be slowed down or accelerated, according to the management of the soil resource.

In laboratory incubation experiment, the researchers initially labelled model bacteria with the stable isotope 13C and introduced the bacteria to soil deriving from the long-term cultivation experiment "Ewiger Roggenbau" in Halle/Saale. Following the incubation time of 224 days the fate of the carbon of bacterial origin was determined. "As a result we found fragments of bacterial cell walls in sizes of up to 500 x 500 nanometres throughout our soil samples. Such fragments have also been observed in other studies, but have never been identified or quantified", declares Professor Matthias Kästner of the UFZ.

...."This new approach explains many properties of organic soil components which were previously viewed as contradictory", says Matthias Kästner....

A canyon formed in the soft loess soil by a small stream that flows from the west into the Daxia He River, in the northeastern part of Linxia County (probably, Xihe Township), in western China. Shot by Vmenkov, Wikimedia Commons,  under the Creative Commons Attribution-Share Alike 3.0 Unported license

First Ever Global Soil Week

Let's Talk About Soil - English from IASS Vimeo Channel on Vimeo.

While soils are the fundamental pillars of sustainable development, they are facing increasing threats. To draw attention to this challenge and to upscale actions towards sustainable soil management, the first ever Global Soil Week was hosted by the Institute for Advanced Sustainability Studies in Berlin from 18-22 November, 2012. The week sought to provide a platform to initiate follow-up actions on land and soil-related decisions made at the Rio+20 Sustainable Development Conference to offer a forum of interactive exchange and dialogue. At the week, stakeholders from science, government, business and civil society came together to share their land and soil-related experience and expertise, and to develop future plans of action for sustainable land/soil management and governance.

Several panels, platform sessions, and dialogue sessions were held on various relevant themes. One of particular interest was a dialogue session on securing the commons co-hosted by Maliasili Initiatives, the Rights and Resources Initiative, and the International Land Coalition. The session “reviewed the state of current knowledge around sustainable use and governance of communal natural resources, and examine threats to communal tenure of lands and resources in a range of different geographic contexts, and from points of reference as varied as gender dimensions, indigenous rights, biodiversity conservation, pastoralist land use, and forest governance.”

Find out more about Global Soil Week here. The International Institute for Sustainable Development's coverage from the week can be accessed here. Find out more about the week’s sessions here. 

Carbon buried in the soil rises again

University of California-Davis News: A research team that includes a University of California, Davis, plant scientist has identified a source of carbon emissions that could play a role in understanding past and future global change. While earlier studies have found that erosion can bury carbon in the soil, acting as a carbon sink, or storage, the new study published this week in the journal Proceedings of the National Academy of Sciences found that part of that sink is only temporary.

“It’s all part of figuring out the global carbon cycle,” said co-author Johan Six, professor of plant sciences at UC Davis. “Where are the sources, and where are the sinks? Erosion is in some ways a sink, but, as we found out, it can also become a source.” The researchers estimated that roughly half of the carbon buried in soil by erosion will be re-released into the atmosphere within about 500 years, and possibly faster due to climate change. Climate change can speed the rate of decomposition, aiding the release of the buried carbon.

As a case study, the researchers used radiocarbon and optical dating to calculate the amount of carbon emissions captured in soils and released to the atmosphere during the past 6,000 years along the Dijle River in Belgium.

The study’s long time scope — from 4000 B.C. to A.D. 2000 — allowed the researchers to notice the gradual reintroduction of buried carbon to the atmosphere. Significant agricultural land conversion — historically the largest source of global erosion — began primarily in the past 150 years, well under the researchers’ time frame of 500 years. Therefore, most carbon sequestered in the soil during the past 150 years of agricultural history has not been released yet but may become a significant carbon source in the future, with implications for soil management, the study said.

“Our results showed that half of the carbon initially present in the soil and vegetation was lost to the atmosphere as a result of agricultural conversion,” said study co-author Gert Verstraeten, a professor at KU Leaven, Belgium. Six noted that erosion could be minimized by no-till and low-till agricultural methods, as well as by cover cropping, which can ensure that soil is not left bare.... 

Long furrows, shot by Duncan Grey, Wikimedia Commons via Geograph UK, under the Creative Commons Attribution-Share Alike 2.0 Generic license