Surface runoff on farms up to five times higher when hill soils are poorly drained

Hill country farms cover more than 60% of NZ’s farm landmass, but – because of their sloping landscapes – the surface runoff when it rains can move sediment and nutrients like nitrogen and phosphorus into streams and lakes, too much of which leads to declining water quality.

Researchers compared nutrient and sediment losses in surface runoff when cattle were fed winter hay supplement on two hill country sub-catchments that had different kinds of soil. The catchment with poorly drained soil had nearly five times more surface runoff – and 4.5 times more total nitrogen – than the area with well-drained soil.

The authors say carefully choosing where cattle are fed in winter, such as in areas with better-drained soil, could reduce nutrient and sediment loss at no cost to farmers.

The research was published in the New Zealand Journal of Agricultural Research (HERE). Continue reading

Midwestern US has lost 57. 6 trillion metric tons of soil due to agricultural practices

A new study in the journal Earth’s Future – led by the University of Massachusetts Amherst – shows that agricultural fields in the midwestern US have lost,  on average, two millimetres of soil a year since Euro-American settlement approximately 160 years ago. This is nearly double the rate of erosion that the United States Department of Agriculture considers sustainable.

Furthermore, USDA estimates of erosion are between three and eight times lower than the figures reported in the study.

Finally, the study’s authors conclude that ploughing, rather than the work of wind and water, is the major culprit.

“A few years back, my wife and I were at a wedding at a pioneer Norwegian church in Minnesota,” says Isaac Larsen, professor of geosciences at UMass Amherst and one of the paper’s co-authors.

“After the ceremony, I walked over to the edge of the churchyard, which was surrounded by cornfields, and was shocked to see that the surface of the field was a few feet lower than the surface of the never-tilled churchyard. I began to wonder why.” Continue reading

Soil slow to respond to native revegetation efforts

Restoration of degraded landscapes takes time and patience, but residual soil deficiencies surprised researchers who compared the results of a six-year native planting project in South Australia.

Revegetation is connected to improved soil health, but Flinders University researchers said their experiment showed a shortfall in soil bacterial recovery after the replantings, highlighting the need for more research into ecosystem restoration.

“We are in the midst of the global biodiversity and land degradation crisis and the UN has just declared a Decade on Ecosystem Restoration,” says senior author Dr Martin Breed, a member of the Frontiers of Restoration Ecology research group and the Health Urban Microbiome Initiative.

“Clearly there is an urgent need and rising demand for effective restoration actions.”

An estimated 75% of the Earth’s land surface is impacted by land degradation and this is projected to rise to almost 90% by 2050, according to the IPBES Assessment Report on Land Degradation and Restoration.

Australia has lost nearly 40% of its forests, with the remaining native forest highly fragmented, with under 4% of Adelaide Plains forest cover and less than 10% of Mount Lofty’s original forest cover remaining since European settlement (Corey Bradshaw, 2012). Continue reading

Nitrogen’s impact on soil carbon sequestration

Soil organic carbon is a cornerstone of soil health. It improves soil structure while enhancing water- and nutrient-holding capacity, key factors for any agricultural production system. To build it up, farmers incorporate crop residues into soils.

So why, despite decades of residue inputs, is soil organic carbon diminishing in corn production systems? Short answer: it’s the nitrogen.

“With intensive nitrogen fertilization, you may get more corn biomass and yield, which means you end up putting more residue into the soil. But you cannot keep that carbon in the soil,” says Richard Mulvaney, professor in the Department of Natural Resources and Environmental Sciences (NRES) at the University of Illinois. 

“The nitrogen in the residues stimulates the microbes to burn carbon off through respiration. So you can put more in, but you can’t keep it.”

The concept that nitrogen fertilization affects residue decomposition — and therefore the incorporation of residue into soil organic matter stores — isn’t new. But previous studies showed conflicting results.

That’s why Mulvaney and Tanjila Jesmin, a doctoral researcher in NRES, set out to clarify how residue quality and the form of nitrogen affect corn residue decomposition in a typical Corn Belt soil.

Thanks to the historic Morrow Plots at Illinois, the team was able to test residues from corn grown with and without high nitrogen fertilization.

“We designed an aerobic incubation study, adding these two residues to a typical cropped soil with or without two forms of nitrogen. We then observed the decomposition process by continuously measuring carbon dioxide production, as well as periodic measurements of enzyme activities and microbial biomass,” Jesmin says.

The researchers found the presence of nitrogen — either exogenously applied to residue or already incorporated in growing corn tissue — accelerated residue decomposition and produced more carbon dioxide. The form of nitrogen applied, potassium nitrate or ammonium sulfate, made no difference.

“The carbon in corn residue comes from the atmosphere, and it returns to the atmosphere during decomposition. That’s not an issue,” Mulvaney says. “The problem is that when microbes have a high nitrogen supply, they also have a high demand for carbon as an energy source. With high nitrogen rates their demand may exceed the carbon supply in residues, which may cause them to attack stable organic matter. And therein lies the long-term problem.”

During the first month of soil incubation, residue carbon decomposition was more rapid in the presence than absence of nitrogen fertilizer. However, carbon dioxide production in the second month was slower for fertilized than unfertilized soil. By the end of the study, the total amount of carbon dioxide produced was greater with than without added nitrogen.

“It’s like burning leaves in the fall. You put more leaves on the fire, and you get more flames. And so, with that added nitrogen, the residue goes more quickly early in the incubation. Then the fire dies down because you had already burned up the readily decomposable substrate. We get there sooner with nitrogen,” he says.

The results explain why soil organic carbon fails to build in high-input cornfields and suggest farmers should avoid excessive nitrogen inputs to maintain soil organic matter.

According to the researchers, further studies are underway to evaluate the effect of mineral nitrogen on residue decomposition in soils with contrasting characteristics.

“Because our incubation utilized a single soil type, the findings might not be valid everywhere. With soils low in native fertility, intensive fertilization is often effective for increasing residue carbon inputs. We want to see if these inputs help to build soil organic carbon,” Jesmin says.

Journal Reference:

  1. Tanjila Jesmin, Dakota T. Mitchell, Richard L. Mulvaney. Short-Term Effect of Nitrogen Fertilization on Carbon

Source:  ScienceDaily

New inexpensive method developed to detect lime in soil

University of Adelaide scientists have developed a new simple, inexpensive and fast method to detect and measure very low concentrations of agricultural lime in soils, which is generally a time consuming and difficult exercise.

The research is published in leading soil science journal Geoderma.

PhD student and lead author of the study Ruby Hume, developed this method as part of a Department of Primary Industries and Regions (PIRSA)-led and Grains Research and Development Corporation-funded project, exploring novel approaches to address the issue of sub-surface soil acidification in South Australia’s cropping regions.

“Soil acidity can be very damaging to crop production. Approximately 20 per cent of agricultural land in South Australia is affected by the problem, and this number is expected to double over the next few decades,” said Ms Hume.

“While it is not a new problem in South Australia, we are now seeing acidity in regions where it has not been an issue previously, such as in the Mid-North and the Yorke Peninsula, and clay-rich soils in the South East.” Continue reading

Getting to the root causes of soil erosion using high-res remote sensing

Soil erosion processes are notably active in New Zealand: our steep slopes, generally weak sedimentary rocks, and high annual rainfall totals including frequent large rainfall events, underscored by a history of vegetation clearance for agriculture, mean that around 192 million tonnes of soil on agricultural land are lost to erosion every year.

Large rainfall events in New Zealand commonly trigger hundreds to thousands of shallow landslides, especially in more marginal pastoral hill country, causing significant damage to land and infrastructure as well as contributing large quantities of sediment to aquatic environments. These landslide inventories are used to determine which land is most susceptible to shallow landsliding to support targeting of erosion control measures.

Within the Ministry of Business, Innovation and Employment research programme Smarter Targeting of Erosion Control (STEC), scientists at Manaaki Whenua have been using new remote sensing techniques to fill these data gaps, mapping over 100,000 landside scars from high-resolution satellite or aerial imagery across the North Island. Continue reading

Adapting roots to a hotter planet could ease pressure on food supply

The shoots of plants get all of the glory, with their fruit and flowers and visible structure. But it’s the portion that lies below the soil — the branching, reaching arms of roots and hairs pulling up water and nutrients — that interests plant physiologist and computer scientist, Alexander Bucksch, associate professor of Plant Biology at the University of Georgia.

The health and growth of the root system has deep implications for our future.

Our ability to grow enough food to support the population despite a changing climate, and to fix carbon from the atmosphere in the soil are critical to our, and other species’, survival. The solutions, Bucksch believes, lie in the qualities of roots.

“When there is a problem in the world, humans can move. But what does the plant do?” he asked. “It says, ‘Let’s alter our genome to survive.’ It evolves.”

Until recently, farmers and plant breeders didn’t have a good way to gather information about the root system of plants, or make decisions about the optimal seeds to grow deep roots. Continue reading

Biofertiliser for better farms – researchers study merits of aquatic cyanobacterial biomass

While agricultural production around the world struggles with declining soil health, researchers are investigating production of a sustainable organic nitrogen fertiliser from aquatic cyanobacterial biomass – ideally suited for badly degraded areas reliant on chemical fertilisers.

“Many soils are degraded and becoming less fertile. This challenges agriculture to produce sufficient high-quality food to feed the continuously growing population, which is further exacerbated by climatic instability threatening crop production,” says Flinders University researcher Associate Professor Kirsten Heimann.

Scientists in Australia, US and Europe are testing a new biofertiliser made from a fast-growing freshwater cyanobacterium Tolypothrix, which can fix nitrogen from the atmosphere without the need for additional nitrogen fertilisation, making the biomass inexpensive to produce compared to alternative microalgal and macroalgal biofertilisers.

This form of non-toxic blue-green algae can be cultivated in freshwater, and even slightly saline or industrial wastewater such as from coal-fired power stations, the research team has found. Capturing biofuel may also be used to offset production costs.

Energy inputs for the production of Tolypothrix biomass can be offset by producing biogas, essentially a methane-rich gas for either drying the biomass to extract high-value health supplement phycocyanin or to produce carbon and nitrogen-rich liquid and solid biofertilisers to remediate soil infertility.

In a recent paper in Chemosphere, Dr Heimann and colleagues in Australia, the US and Spain investigate Tolypothrix production as a sustainable solution for biological soil improvement, which when combined with biogas or the spirulina-like nutritional powder promises “strong economic returns for regional and remote farming communities”.

“Australian soils, in particular in the marginal wheat belt in Western Australia, are structurally degraded, which cannot be overcome by applications of synthetic fertilisers,” says Associate Professor Heimann, from the Flinders University Centre for Marine Bioproducts Development in Adelaide, South Australia.

“To improve soil structure, organic carbon applications are required to return the soils’ capacity to sustain a healthy soil microbiome and to improve the soils’ cation exchange of nutrients and water-holding capacity.”

Researchers say conversion of pond-produced cyanobacterial biomass produced on farming land would provide a major in-situ source of renewable nitrogen-rich fertiliser, also helping to reduce carbon emissions from chemical fertiliser production and transport.

Higher energy and food demands are forecast as a consequence of expected global population growth, predicted by the UN to reach 8.5 billion in 2030, 9.7 billion by 2050 and 10.9 billion in 2100.

These projections encourage research into biofertilizer and biogas production through sustainable energy generation using waste organic material of controlled production of biomass such as microalgae and multicellular cyanobacteria.

Researchers have previously reported photosynthetic fixation of CO2 by cyanobacteria of 100 to >200 tons CO2 ha−1 y−1 under outdoor cultivation conditions in open ponds, raceway ponds, photobioreactors and attached growth bioreactors.

Unlike many cyanobacterial species, Tolypothrix sp., a freshwater cyanobacterium, is filamentous and forms aggregates that self-flocculate, making it very easy to harvest from suspension cultures, reducing dewatering costs by up to 90%, studies suggest.

The article, Biomass pre-treatments of the N2-fixing cyanobacterium Tolypothrix for co-production of methane (2021) by C Velu, OP Karthikeyan, DL Brinkman, S Cirés and K Heimann has been published in Chemosphere (Elsevier) DOI: 10.1016/j.chemosphere.2021.131246

Link to research (DOI): 10.1016/j.chemosphere.2021.131246

Source:  Scimex

New book extols the value of high-class New Zealand soils

A ground-breaking new book, The Soils of Aotearoa New Zealand, will launch during the joint New Zealand-Australia soils conference at the University of Waikato on Monday 28 June.

Published as part of the World Soils Book Series by Springer, the book is the first of its kind to be released in almost three decades, says one of its co-authors, University of Waikato soil scientist Professor David Lowe.

The  book builds on the widely used title, New Zealand Soil Classification, first published in 1992.

Its three authors – Dr Allan Hewitt, from Manaaki Whenua Landcare Research, and Dr Megan Balks and Professor David Lowe, from Te Aka Mātuatua School of Science at the University of Waikato, among them have more than 110 years of experience in soil science. Continue reading

Native plants may be weapon against soil contamination

New Zealand’s native plants may help to reduce bacterial contamination caused by dairy effluent, a new study suggests.

Researchers from the Bio-Protection Research Centre, ESR, and the University of Canterbury have shown northern rātā (Metrosideros robusta) and swamp mānuka (Leptospermum scoparium) can reduce the amount of Escherichia coli (E. coli) in soil by 90%, compared with ryegrass (Lolium perenne), and in less than one-third of the time. They worked in partnership with Ngaa Muka Development Trust and Matahuru Marae in Waikato.

The research, published in Applied Soil Ecology, aimed to investigate the antimicrobial properties of New Zealand native plant extracts and test if they were effective in soil. Continue reading