Archive for the ‘Soil science’ Category

Decomposing leaves are shown to be a source of nitrous oxide

Michigan State University scientists have pinpointed a new source of nitrous oxide, a greenhouse gas that’s more potent than carbon dioxide.

The culprit?

Tiny bits of decomposing leaves in soil, according to account of the research released by the univerity (HERE).

The discovery, featured in the current issue of Nature Geoscience, could help refine nitrous oxide emission predictions as well as guide future agriculture and soil management practices.

“Most nitrous oxide is produced within teaspoon-sized volumes of soil, and these so-called hot spots can emit a lot of nitrous oxide quickly,” said Sasha Kravchenko, MSU plant, soil and microbial scientist and lead author of the study.

“But the reason for occurrence of these hot spots has mystified soil microbiologists since it was discovered several decades ago.”

Part of the vexation was due, in part, to scientists looking at larger spatial scales. It’s difficult to study and label an entire field as a source of greenhouse gas emissions when the source is grams of soil harboring decomposing leaves.

Changing the view from binoculars to microscopes will help improve N2O emission predictions, which traditionally are about 50 percent accurate, at best. Nitrous oxide’s global warming potential is 300 times greater than carbon dioxide, and emissions are largely driven by agricultural practices.

“This work sheds new light on what drives emissions of nitrous oxide from productive farmlands,” said John Schade, a programme director for the National Science Foundation’s Long-Term Ecological Research program, which co-funded the research with NSF’s earth sciences division.

“We need studies like this to guide the creation of sustainable agricultural practices necessary to feed a growing human population with minimal environmental impact.”

To unlock the secrets of these N2O hotspots, Kravchenko and her team took soil samples from MSU’s Kellogg Biological Station Long-term Ecological Research site.

Then in partnership with scientists from the University of Chicago at Argonne National Laboratory, they examined the samples at Argonne’s synchrotron scanning facilities, a much more powerful version of a medical CT scanner. The powerful X-ray scanner penetrated the soil and allowed the team to accurately characterize the environments where N2O is produced and emitted.

“We found that hotspot emissions happen only when large soil pores are present,” Kravchenko said. “The leaf particles act as tiny sponges in soil, soaking up water from large pores to create a micro-habitat perfect for the bacteria that produce nitrous oxide.”

Not as much N2O is produced in areas where smaller pores are present. Small pores, such as in clay soils, hold water more tightly so that it can’t be soaked up by the leaf particles. Without additional moisture, the bacteria aren’t able to produce as much nitrous oxide. Small pores also make it harder for the gas produced to leave the soil before being consumed by other bacteria.

“This study looked at the geometry of pores in soils as a key variable that affects how nitrogen moves through those soils,” said Enriqueta Barrera, program director in NSF’s earth sciences division. “Knowing this information will lead to new ways of reducing the emission of nitrous oxide from agricultural soils.”

More specifically, future research will review which plant leaves contribute to higher N2O emissions. Plants with more nitrogen in their leaves, such as soybeans, will more than likely give off more N2O as their leaves decompose. Researchers also will look at leaf and root characteristics and see how they influence emissions.

Soil scientist goes myth-busting about feeding the world with fewer chemicals

Three big myths that impede our ability to restore degraded soils and feed the world using fewer chemicals are tackled in an essay in The Conversation, an online publication covering the latest research.

The essay, written by David R. Montgomery, has been reprinted in Scientific American (HERE).

Montogmery is a Professor of Earth and Space Sciences at the University of Washington in Seattle, where he is a member of the Quaternary Research Center. Wikipedia

One of the biggest modern myths about agriculture he now confronts is that organic farming is inherently sustainable,

It can be, but it isn’t necessarily.

Montgomery then addresses other issues which he says must be recognised to restore degraded soils to feed the world using fewer agrochemicals.

He embarked on a six-month trip to visit farms around the world to research his forthcoming book, “Growing a Revolution: Bringing Our Soil Back to Life.

The innovative farmers he met showed him that regenerative farming practices can restore the world’s agricultural soils.

In both the developed and developing worlds, these farmers rapidly rebuilt the fertility of their degraded soil, which then allowed them to maintain high yields using far less fertiliser and fewer pesticides.

Their experiences, and the results that I saw on their farms in North and South Dakota, Ohio, Pennsylvania, Ghana and Costa Rica, offer compelling evidence that the key to sustaining highly productive agriculture lies in rebuilding healthy, fertile soil.

But the journey also led Montgomery to question three pillars of conventional wisdom about today’s industrialised agrochemical agriculture:

MYTH 1: LARGE-SCALE AGRICULTURE FEEDS THE WORLD TODAY

Not so. He cites a recent UN Food and Agriculture Organization (report which says family farms produce over three-quarters of the world’s food. The FAO also estimates that almost three-quarters of all farms worldwide are smaller than one hectare – about 2.5 acres, or the size of a typical city block.

Of course the world needs commercial agriculture, unless we all want to live on and work our own farms. But are large industrial farms really the best, let alone the only, way forward?

MYTH 2: LARGE FARMS ARE MORE EFFICIENT

While mechanisation can provide cost and labor efficiencies on large farms, bigger farms do not necessarily produce more food. Large farms excel at producing a lot of a particular crop – like corn or wheat – but small diversified farms produce more food and more kinds of food per hectare overall.

MYTH 3: CONVENTIONAL FARMING IS NECESSARY TO FEED THE WORLD

The most extensive yield comparison to date, a 2015 meta-analysis of 115 studies, found that organic production averaged almost 20 per cent less than conventionally grown crops, a finding similar to those of prior studies.

But the basis for claims that organic agriculture can’t feed the world depend as much on specific farming methods as on the type of farm.

Moreover about a quarter of all food produced worldwide is never eaten. Each year the United States alone throws out 133 billion pounds of food, more than enough to feed the nearly 50 million Americans who regularly face hunger.

So even taken at face value, the oft-cited yield gap between conventional and organic farming is smaller than the amount of food we routinely throw away.

In the upshot, Montgomery says he no longer sees debates about the future of agriculture as simply conventional versus organic.

He now sees adopting farming practices that build soil health as the key to a stable and resilient agriculture.

And the farmers he visited had cracked this code, adapting no-till methods, cover cropping and complex rotations to their particular soil, environmental and socioeconomic conditions.

Whether they were organic or still used some fertilizers and pesticides, the farms I visited that adopted this transformational suite of practices all reported harvests that consistently matched or exceeded those from neighboring conventional farms after a short transition period.

Another message was as simple as it was clear: Farmers who restored their soil used fewer inputs to produce higher yields, which translated into higher profits.

Study of nitrous oxide emissions from cattle urine deposited on soil supporting kale crop

The New Zealand Journal of Agricultural Research plays an important role in disseminating topical information to researchers in universities, research institutes, and other centres concerned with animal or pastoral science.

The journal publishes original research papers, review papers, short communications, book reviews, letters, and forum articles. Subject matter includes soil science, fertilisers, insect pests, plant pathology, weeds, forage crops, management systems, agricultural economics, agronomy, and animal science.

Recent articles include a study of nitrous oxide emissions from cattle urine deposited on to soil supporting a winter forage kale crop.

The authors are . J. van der Weerden, T. M. Styles, A. J. Rutherford, C. A. M. de Klein & R. Dynes.

The abstract says:

Wintering cows on forage crops leads to urine being excreted onto wet, compacted soils, which can result in significant emissions of nitrous oxide (N2O).

A field trial was conducted to determine the N2O emission factor (EF3; proportion of urine-N lost as N2O-N) for dairy cows wintered on a kale forage crop on a poorly drained soil. Urine was collected from non-lactating dairy cows on a forage kale diet and applied at 550 kg N ha−1 to artificially compacted soil to simulate trampling and non-compacted soil in a kale field.

Cumulative N2O losses over four months were 7.38 and 2.64 kg N2O-N ha−1 from urine applied to, respectively, compacted and non-compacted soil. The corresponding EF3 values 0.75% and 0.30%, respectively, differed (P = .003) due to compaction.

Combining these results with previous studies, where brassica-fed livestock urine was applied to soils supporting a forage brassica crop, suggests a significant relationship between soil water-filled pore space (WFPS) and brassica-derived urine EF3 (P = .005).

US measure of age in soil nitrogen could help more precise fertiliser applications

University of Illinois engineers are reported to have developed a model to calculate the age of nitrogen in corn and soybean fields, which could lead to improved fertiliser application techniques to promote crop growth while reducing leaching.

Civil and environmental engineering professor Praveen Kumar and graduate student Dong Kook Woo published their work in the journal Water Resources Research.

“By understanding how long nitrogen stays in the soil and the factors that drive that, we can improve the precision at which we apply nitrogen for agriculture productivity,” said Kumar, also a professor of atmospheric sciences.

“We may be able to apply fertiliser specifically in areas that are deficient in nitrogen, in precisely the amount that the plants need to uptake, rather than just applying it uniformly. Potentially, we could see a significant reduction in fertiliser amounts.”

Plants take up nitrogen from the soil through their roots as a nutrient. Nitrogen is added to the soil through fertiliser application or by microbes in the soil breaking down organic compounds. But when there is more nitrogen in the soil than the plants need, it leaches into the water and can accumulate in lakes, rivers and oceans.

“Nitrogen, usually in the form of nitrate fertiliser, is needed for healthy crop production, but too much is not a good thing since the excess can contaminate water supplies,” said Richard Yuretich, program director in the National Science Foundation’s Division of Earth Sciences, which funded the research.

“Knowing how long nitrate resides in the soil will lead to more efficient agriculture that maximises plant health without overdosing the environment.”

Kumar and Woo developed a numerical model to calculate how long inorganic nitrogen has been in the soil, using a corn-corn-soybean rotation common in the Midwest. Fresh fertiliser application or microbial production of nitrates and ammonium are considered “birth,” or age zero. The researchers then computed age by the chemical reactions or transformations nitrogen goes through in the soil, mediated by moisture, temperature and microbes.

The model revealed two surprising findings when comparing the average age of nitrogen in the topsoil with that in deeper layers, and in comparing corn fields with soybean fields.

“The biggest surprise to me was that we found a lower average age of nitrogen in soybean fields,” Woo said. “We use fertiliser on corn, not soybeans. Yet even though we count that fresh fertiliser as age zero, we found a lower average age of nitrogen in soybean fields. We found that is mainly because soybeans uptake the old nitrogen, so the average age is reduced.”

When looking at the layers of soil, the researchers initially expected that nitrogen would follow a similar age path to water: newer on top, and growing older as it migrates down through the soil. Instead, they found the nitrogen topsoil had a relatively high average age when compared with the water. Looking closer, they realised that one of the forms of nitrogen, ammonium, accumulated in the topsoil.

“Ammonium has a positive charge, which adheres to the soil particles and prevents it from leaching to the deeper layers,” Woo said. “Because of that, we observe relatively higher nitrogen age in the upper layers, compared with the age of the nitrate that dissolves in water, which doesn’t have that barrier and can migrate down through the soil.”

The researchers have established a field site to validate their model by analysing the isotopic composition of nitrogen, oxygen and water in the runoff. They hope their work can help farmers more efficiently use resources while reducing contamination of water sources and marine habitats.

 

Canadian researchers study vineyard effects on soil quality

University of British Columbia biologists are digging under vineyards to see if the Okanagan’s grape industry is affecting soil quality.

A news release from the university says Miranda Hart, an associate professor of biology at UBC’s Okanagan campus, her PhD candidate Taylor Holland, and Agriculture Canada research scientist Pat Bowen, have spent some three years studying soil samples from more than 15 vineyards throughout the Okanagan.

Specifically, they were looking at soils in vineyards and neighbouring natural – or uncultivated – habitats. With samples from both areas, the scientists compared the bacterial and fungal communities between these habitats, hoping to determine what is happening to the soil under the wine-producing grapes.

They determined there was a definite difference in soil communities between the natural valley soil and the vineyard soil.

“Soil biodiversity may be an important part of terroir, which is everything to a grape grower, so they have a vested interest in ensuring we preserve soil biodiversity,” says Hart.

“This baseline study shows us that BC wine growing regions are different in terms of the organisms that live in the soil.”

All agricultural activity will affect the soil, some more than others, Hart explains. But to know how the soil is being changed, researchers wanted to compare samples with natural, uncultivated areas alongside processed areas.

“We have to take care of the microbes in the soil,” she says. “The biodiversity of soil microbes is essential if we are to feed our growing population.”

While Hart points out there is a limited understanding of how agriculture practices change soil biodiversity, it is important to understand what the soil would be like if left in its natural state, so growers are aware of how they may be changing it.

The samples they tested showed that bacterial and fungal communities responded differently to viticulture: bacteria had a higher biodiversity in vineyards, compared to fungi which had higher biodiversity in unmanaged areas.

These results indicate that viticulture practices influence key environmental factors that control soil microbial communities and possibly affect nutrient availability and other services provided by natural soil communities, says Holland. Microbes are big part of the soil for grape growers; what happens underground can influence the vine growth and fruit development and downstream wine assets, he explains.

“Improved knowledge of how management choices affect microbial communities and their influences on crop performance would benefit the design of efficient and sustainable production systems,” Holland says.

“As we move towards more natural practices, hopefully we can reduce these differences.”

Bowen, who works at the Summerland research centre, says knowing what’s happening in the soil is a vital part of agriculture for several reasons.

Microbial communities also play an important role in stabilising vineyard ecosystems which can reduce the need for pesticides and other resource inputs, he says.

Hart’s research, funded by an NSERC Discovery Grant, and other funds provided by the British Columbia Wine Grape Council and Agriculture & Agri-Food Canada, was recently published in Applied Soil Ecology.

Soil science conference in Queenstown in December

The joint conference of the New Zealand Society of Soil Science and Soil Science Australia will be held in Queenstown in December.

The overarching theme of the conference is “Soil, a Balancing Act Down-under” and reflects the challenges we are facing in managing our soils to reach a careful balance between many, often competing, land-use, productivity and environmental aspirations.

A central question of the conference is “What is required from soil science and soil scientists, now and in the future, to enable society to achieve the balance?”

Details: 12-16 December 2016, Millennium Hotel, Queenstown, www.nzsssconference.co.nz

 

Soil researcher surprised by findings from dairy farm field work on urine patches

Unexpected and conflicting results from research around irrigation practices and their influence on greenhouse gas emissions have Lincoln University PhD student Jen Owens contemplating a more complex scenario and a few possible explanations.

Ms Owens carried out a field experiment on a commercial dairy farm measuring nitrous oxide emissions and soil oxygen concentrations under urine patches subjected to varying rates of irrigation. Her studies are integrated with a three-year research programme by Landcare Research into greenhouse gas emissions from intensive dairying.

Nitrous oxide is a potent greenhouse gas linked to climate change. Most of New Zealand’s nitrous oxide emissions come from grazed pastures where soil is affected by nitrogen inputs such as ruminant urine. Nitrous oxide emissions from urine patches are a problem for New Zealand given the intensification of dairying.

“While many dairy farms are using irrigation to improve pasture production to meet the nutritional needs of their cows, little is known about what happens to the nitrous oxide emissions from urine patches when they are irrigated,” says Ms Owens.

Her field experiment explored the possibility that irrigation may modify soil oxygen concentrations, potentially reducing nitrous oxide emissions from urine patches. She found that soil oxygen concentrations under a more frequently irrigated urine patch were lower when compared to a less frequent irrigation regime.

These lower soil oxygen concentrations were expected to lead to lower nitrous oxide emissions. However, this didn’t happen, suggesting a more complex scenario.

“Nitrous oxide emissions were not affected by irrigation frequency but we were surprised to find the more frequent irrigation rate lead to potentially greater nitrous oxide uptake by microbes. These two results appear to conflict with each other.”

A possible explanation for this is that the potential for the production of nitrous oxide has increased in response to lower soil oxygen, as well as the potential for soil microbes to consume nitrous oxide. So in effect we are measuring the net effect of these two processes.”

Based on the results from the study, Ms Owens has performed a number of smaller experiments under controlled conditions to better understand how soil biology is driven by the soil’s physical status.

She said:

“These experiments have helped us interpret how irrigation influences nitrous oxide emissions from urine patches.

“We’ve also started looking at urine patch induced nitrous oxide emissions on other soil types and during different times of the year, winter instead of summer, to validate and further explore the impact of soil oxygen concentrations.”

Ms Owens’ research is being funded by Landcare Research.