Lynn Brandenberger, Professor of Horticultural Food Crops, Oklahoma State University, and Ajay Nair Associate Professor of Extension Vegetables, Iowa State University, discuss the importance of soil care for crop production, especially as it relates to organic matter of the ground

Why should people be interested in being soil keepers? Whether we have a vegetable or animal diet, the soil is at the origin of everything. Feeding the soil to feed the plant is a basic principle of the sustainable agricultural system. Therefore, it is incumbent upon us to be good stewards of the soil to secure future food and fiber supplies. When food and fiber supplies are scarce, societies do not survive long and life can easily slip from semblance of order into chaos.

Soils are the foundation of our food production system while providing other essential services related to water, air and climate. Soils are made up of inorganic and organic materials in a matrix that also includes materials in liquid and gaseous form. The inorganic comes from the rock (parent material) which eventually weathers into what we think of as soil particles (sand, silt, clay) which determine the texture of the soil. There is not much we can do to alter the texture of the soil, which means that in the field the percentage of sand, silt or clay in the soil will more than likely remain unchanged. Organic matter comes from plants, microflora (fungi, bacteria, protozoa) and animals. Soils serve as a carbon bank in that some have estimated that globally, soils hold four times more carbon in the environment than living plants (Magdoff and Van Es, 2009).

Organic material

Soil organic matter is one of the main indicators of soil health and is fundamental to the long-term sustainability of agroecosystems (Larkin, 2015). Organic matter (OM) can modify the physical, chemical and biological characteristics of soils.

OM additions can increase biological activity in soil to improve plant nutrient availability (OM mineralization), detoxify soil pollutants (bioremediation), increase soil particle aggregation which in turn increases water uptake and storage, and it can improve soil condition (workability). Organic matter is constantly mineralized by soil microbial life and as such, crop growers should consider that additional OM will need to be added regularly to maintain the carbon balance in the soil. Intensive agricultural production practices are not conducive to the preservation of OM and soil quality as they can lead to soil erosion, soil organic matter (SOM) depletion, soil structure deterioration , increased greenhouse gas emissions, biodiversity losses and lead to poor soil quality and reduced harvests. yields (Stavi et al., 2016). Much has been written about the loss of productive agricultural soils to erosion, loss of organic matter and losses due to urbanization. Soils that have been overgrown and damaged can be recovered by adding organic matter, so it is possible to regenerate soils that have become unproductive.

There are a wide range of sources to consider when adding organic matter to improve soil fertility, quality and health. Each farm has its own soil types, sources of organic matter, and equipment for applying and incorporating OM. Decisions should be based on cost, availability, convenience, and generally what works best for a particular farm. Sources can range from compost, manure, animal litter to cover crops and other plant matter. A potential issue for sources is whether the material being considered for use may contain herbicide residues. This is especially true when using grass hay, grass clippings, or compost made from either if they have been treated with herbicides. A simple bioassay using a sensitive species such as tomato or spinach to test for the presence of herbicide residues is good practice.

Other factors affecting organic matter selection could include time and space for composting, food safety risks associated with manure-based soil amendments, and storage of materials prior to application. Cover crops are an alternative to the aforementioned MO sources, but consider that growing cover crops will remove field areas from production for the duration of their cultivation. Therefore, there are no clear alternatives for improving soil MO, each should be carefully considered before use. Organic amendments, including manure, cover crops, and compost, help improve soil quality and health because they improve the activity and abundance of organisms that break them down in the soil (Nair and Ngouajio, 2012).

Soil research studies

Research on increasing soil OM may include different tillage systems and adding organic matter to improve the soil. In Oklahoma, we investigated cover crops for soil improvement by comparing different cover crops to a fallow system with no added organic matter. Although the results were not dramatic, we saw a slow but steady increase in soil organic matter levels in the cover crop treatments and a significant decrease in OM in the fallow system. The jury is still out on crop yields, but there is a trend towards higher yields.

Raimbault and Vyn (1991) reported increases in maize yields through crop rotation compared to continuously grown maize with different cultivation practices also varying in yield. Their most dramatic yield differences were recorded for crop rotation combined with a minimum tillage system. A study conducted in western Colorado in the United States reported less erosion, improved water infiltration rates and higher soil water content with conservation tillage methods compared to conventional tillage (Ashraf et al. 1999). In Iowa, cover crop-based conservation tillage systems have been shown to be viable options for organic broccoli and pepper production (Jokela and Nair, 2016).

Studies in Connecticut have indicated that soil organic matter amounts have a direct effect on productivity, with increases in soil OM stocks being directly related to increased productivity (Oldfield et al. 2018). In the UK, Johnston (1986) reported higher yields on soils that received additional organic matter in sandy and silty loams, soils with higher MO had better water holding capacity, increased nitrogen availability and better response to nitrogen fertilizers. body of evidence confirming that the addition of organic matter (manure, compost, cover crops, mulch, etc.) and reduced tillage improve the physical, chemical and biological properties of the soil and increase the organic C stores in the ground. A systems approach to production is needed to identify and understand the importance of the links between producer practices and their implications for crop growth, yield, productivity, soil quality and health, and the environment.

In vegetable production systems, enterprise diversity, farm size and scale, soil type, market and labor demands, and climatic conditions provide opportunities and/or unique barriers to improving the overall sustainability of our cropping systems. Several grower-run professional organizations and societies such as the Soil Science Society of America, American Society for Horticultural Science, International Society for Horticultural Science, Entomological Society of America, American Phytopathological Society, European Society for Soil Conservation and several other soil science societies in Europe, all work to preserve and protect the current agricultural system.

As we move towards our shared goal of building resilient soils, we must recognize that much work is needed to help growers develop and adopt production practices and strategies that improve the overall productivity of their cropping systems without jeopardize economic, social and environmental benefits. sustainability of their communities.

Quotes:

Ashraf, M., Pearson, C., Westfall, D. and Sharp, R. 1999. Effect of conservation tillage on crop yields, soil erosion and in-furrow irrigation soil properties in the western Colorado. American Journal of Alternative Agriculture, 14(2): 85-92.

Johnston AE 1986. Soil organic matter, effects on soils and crops. Land Use and Management, Volume 2, Number 3: 97-105.

Jokela, D. and Nair, A., 2016. Effects of reduced tillage and fertilizer application method on plant growth, yield and soil health in organic pepper production. Tillage Research 163: 243–254.

Larkin, RP 2015. Soil health paradigms and implications for disease management. Annual Review Phytopathology Vol. 53:199-221.

Magdoff, F. and Van Es, H. 2009. Building Soils for Better Crops Sustainable Soil Management – Sustainable Agricultural Research and Extension Handbook #10.

Nair, A. and Ngouajio, M. 2012. Soil microbial biomass, functional microbial diversity and nematode community structure affected by cover crops and compost in an organic vegetable production system Applied Soil Ecology 58:45– 55.

Oldfield, EE, Wood, SA, and Bradford, MA 2018. Direct effects of soil organic matter on productivity mirror those seen with organic amendments. Topsoil 423: 363–373.

Raimbault, BA and Vyn, TJ 1991. Effects of crop rotation and tillage on maize growth and soil structural stability. Journal of Agronomy: 83: 979-985.

Stavi, I., Bel, G. and Zaady, E. 2016. Soil functions and ecosystem services in conventional, conservation and integrated farming systems. A review. Agro. To support. Dev. 36:32.

Ajay Nair

Associate Professor Specialist in plant extension

Iowa State University

Tel: +1 515 294 7080

[email protected]

www.extension.iastate.edu/vegetablelab

*Please note: This is a commercial profile

© 2019. This work is licensed under CC-BY-NC-ND.

Long before the emergence of the carbon market that offered economic incentives for farmers to adopt soil conservation practices such as no-till and cover crops, Jack Boyer had already discovered the value of these practices.

In the mid-1990s, Boyer, a corn and soybean farmer from Reinbeck, Iowa, began planting his soybeans without tillage. No-till planting in commercial corn came later, as did his early on-farm experiments with cover crops.

On-farm research has shown him that cover crops can help him reduce chemical applications, reduce nitrogen inputs and eliminate the cost of cleaning up eroded soil buildup from streams. All the while, cover crops were building soil organic matter.

“Initially, I switched from conventional tillage to no-till soybeans to save labour,” says Boyer. He and his wife, Marion, farm some 750 acres without outside help.

“I was also interested in conserving moisture because I first grew on really sandy soils,” he says. “But now I’m growing very productive soils.”

Three-pronged objective

The Boyers’ desire to leave the soil better than they found it prompted them to try cover crops. Of most concern was the degradation of soil organic matter after decades of tillage resulting from part of the farm’s family history in a rotation of seed corn and soybeans.

The seed corn business for which the family grew seed required “black” soil conditions between the rows. “As a result, the soil contained only 2.5 percent organic matter, compared to 6 percent in the fences, where perennial grasses grew without soil disturbance,” Boyer says.

A presentation at a conference inspired the idea that growing cover crops could create organic matter even in plowed fields producing seed corn. “We had a three-pronged goal growing cover crops,” Boyer explains. “We wanted them to build organic matter, control erosion and improve nutrient cycling.”

His first experience growing cover crops was planting just 50 acres of annual ryegrass in seed corn. “I flew the ryegrass seeds in mid-September,” he says. “It came out and looked good, reaching 3-4 inches tall. But it froze in the winter. That’s a problem for us because our goal is to have live roots in the ground the most days. possible.

Still committed to on-farm research, Boyer tried another try in the second year. He planted an additional 50 acres of annual ryegrass and an additional 50 acres of cereal rye in a different field. “The ryegrass froze again,” he says, “but the cereal rye sprouted in the spring and grew rapidly after the temperature hit 50°F.”

As a result, cereal rye became his favorite cover crop species, and today 100% of the farm’s acres are planted with a cover crop. A multi-species cover grows on a small area of ​​land where Boyer grows grain rye to harvest the seeds to use for his own cover crops. He also sells cover crop seeds and uses them in the custom cover crop planting he does.

The July harvest of rye for seed allows time for a mixture of warm season multi-species cover crops to establish before winter and further strengthen the soil. “I add rapeseed to the mix, and 25% of the rapeseed will overwinter; everything else will be killed by winter,” he says.

Boyer no-till plants all commercial corn and soybeans. He can also now use the strip-till to plant seed corn, as the seed company has relaxed tillage requirements.

Improved Soil Health

The combination of growing cover crops and reducing tillage has improved soil health. “Over the past 10 years, we have seen soil organic matter increase by 1%,” he says. “He is now testing for 3.5% organic matter, even on fields that are long-term seed corn fields. The increase in organic matter improves the water holding capacity in the soil as well as the nutrient holding capacity. It makes nutrients available longer.

“The soil structure has also improved,” he says. “The soil used to be a plate-like structure, now it has a structure like cottage cheese. This allows more air into the soil, allowing more soil biology to live. seep into the ground.

Boyer noticed the benefits of better water infiltration after just one year of growing cover crops. His first experience growing grain rye was in a field that had been rotated with soybeans and seed corn for 70 years. “After a heavy rain, we would usually see water pooling on that field,” he says. “But on the part of the field where we had 50 acres of grain rye, there was no pooling after a big rain.”

In addition to improving the soil structure, “soil erosion has disappeared,” he adds. “Before we grew cover crops, I had to clean the waterways every seven years. I haven’t had to clean them at all since we started growing cover crops. It’s money saved.

Another cost offset Boyer realized from growing a cover crop was the elimination of a herbicide application. In an on-farm trial conducted in conjunction with Practical Farmers of Iowa (PFI), he evaluated the effect of cover crops on weed control.

In one field, he had alternated strips of cover crops with strips without cover crops. All strips were to be planted with no-till soybeans. He finished grain rye in some cover strips 10 days before planting, and in other strips he finished rye 10 days after planting. “The rye was 24 inches tall when I planted the soybeans,” he says.

In June, weed growth was evident in soybeans planted where there was no cover crop, but not in either cover crop treatment. “At the end of June, I just sprayed the strips where there was no cover crop,” he says. “These savings would have been more than enough to pay for the cost of cover crop seeds.”

Boyer continued to experiment by letting the rye grow before finishing it. “I found that finishing the rye even when it was bigger made no difference in yield,” he says. “The soybeans growing in the cover crops always looked two weeks behind, but in the end there was no difference in yield. My preference now is to plant soybeans in rye about 4 feet tall.

Reduced nitrogen use is another cost saving Boyer achieves with its no-till/cover crop system. “I found that I could reduce the amount of nitrogen I was applying to corn by 40 percent,” he says. “I believe the biological life in the soil makes natural nitrogen more available to plants. This saving more than pays for the cost of cover crop seeds.

Despite reduced N use, Boyer found no decrease in yields of untilled commercial maize.

An additional potential saving results from the nitrogen that the cover crop recovers and makes available to the following crop. In a field trial Boyer did with PFI, he found that the cover crop captured 66 pounds per acre of N. “The cover crop prevents that amount of N from potentially leaching out,” he says. “After ending the cover crop in the spring, the N then becomes available for the next crop.”

Reports of on-farm trials from Boyer and others with the PFI are available at practicefarmers.org/research/.

“I speak publicly about cover crops,” adds Boyer, who has been named a soil health champion by the National Association of Conservation Districts. “By sharing my experiences – good and bad – I hope I can help others learn how to use cover crops to their advantage.”

The new insights can help new users of no-till and cover crops better position themselves to find potential opportunities in the carbon market. “Adopting strip-till, no-till, cover crops or finding ways to reduce nitrogen – each of these is a step towards earning carbon credits,” he says.

Why soil organic matter is important

The floors are a mixture of:

• mineral matter (sand, silt and clay) – their ratio determines the texture of the soil
• air
• the water
• organic material

Organic matter is a small but vital part of soil. It is composed of :

• living organisms, such as bacteria, fungi, plant roots, and small animals
• decaying plant or animal tissue

Organic matter is important for better soil fertility and structure, and for overall soil health. To increase organic matter levels, you can:

• add organic materials such as solid or liquid manure, plants or crop residues
• reducing soil drainage or cultivation to slow the breakdown of organic matter

You must follow the agricultural rules for water. These require you to take steps to prevent manure, fertilizer or soil from entering water bodies.

Where to increase soil organic matter

Priority :

• soil with less than 15% organic matter in the top 15 cm
• arable or root crops where the previous growth of the crop is destroyed (usually by plowing or spraying) before planting

The benefits of soil organic matter

Soil with more organic matter can absorb and hold more water. This can improve crop productivity and reduce:

• tillage and irrigation costs
• flooding, as water moves more slowly across the landscape after heavy rains
• erosion and runoff
• greenhouse gas emissions
• need for fertilizer, as nutrients are recycled more efficiently
• the use of pesticides, as more organic matter will reduce pests and diseases

Soils low in organic matter are more prone to wind erosion, especially sandy soils. The increase in organic matter will bind topsoil to help prevent wind and associated airborne particle pollution.

Before you start increasing soil organic matter

Use a runoff and soil erosion risk assessment to verify and record:

• fields with eroded soil or streams
• wind erosion – look for buried seedlings and blown soil in hedges or ditches, or on nearby roads

Soil pits are a quick way in the field to check your soil for:

• shallow rooting depth
• slow water infiltration
• low number of earthworms
• poor or weak soil structure

Read a guide to visually check the floor.

How to Measure Soil Organic Matter Levels

Take soil samples and send them to a lab for analysis. Compare the results with findings from your soil pits and soil mapping data.

For accurate results:

1. Sample areas with roughly the same soil type and history.
2. When fields include more than one soil type, sample each separately.
3. Collect 25 individual soil cores, in a clean plastic bag, to form a bulk sample of approximately 0.5 kg.
4. Take the cores in a “W” pattern, with 5-7 cores along each leg of the “W”.
5. Avoid uneven areas of terrain, such as manure piles, pylons, walkways, headlands, and around trees.
6. Sample at the same time each year, but do not sample if the soil is waterlogged or very dry.
7. Do not sample within 3 months of spreading manure or slurry as this will affect organic matter levels.

Take grassland cores at 7.5cm depth and topsoil cores at 15cm. A plowed layer is usually 23 cm deep, but if the soil in this layer is mixed, a 15 cm sample will be representative.

If you are using a no-till or no-till crop, nutrients can accumulate near the surface of the soil. A 15 cm sample may give too high readings, so sample at about 23 cm. Read a guide to sampling different cultures.

Your lab results should also include soil texture. Clay content influences the amount of organic matter a soil can normally store. Use your results to identify fields with below average soil organic matter.

How to Add Organic Matter to Soil

You can:

If your soil is slow to warm up in the spring and delays germination, sow later. The overall benefits for growing higher levels of organic matter should balance this out.

Add organic matter to soil from:

• animal manure and slurry, from your own farm or imported from elsewhere
• digestate (material left over from anaerobic digestion of biodegradable materials, such as household food waste)
• manure or specialty crops
• composts and biosolids
• paper and wood crumble
• slaughterhouse and food processing by-products

Check to see if you can get financing for new precision manure spreading equipment.

You can allow soil organisms to mix with the added organic matter, instead of using machinery. Use this natural process only when:

• the condition of the ground is good
• the risk of runoff is low
• earthworms are abundant

Using lab results, add to areas low in organic matter. You should follow best practices for using sewage sludge on your land. You may also need a land application permit.

Record organic matter inputs with a nutrient management plan. It will help you:

• avoid wasting money by using too much fertilizer
• optimize crop yields
• minimize nutrient pollution of water and air

Use cover crops or green manures and catch crops on land at high risk of pollution, instead of slurry or fertilizer.

Use ground cover and low-emission spreading equipment, such as a hose or drag shoe, to prevent soil crusting when slurry is applied to bare soil. Low-emission spreading equipment will limit ammonia loss and ensure more nutrients reach the soil.

How to Reduce Soil Organic Matter Loss

You can:

• add harder organic materials with a high carbon to nitrogen ratio like straw, crumbled paper, sawdust or wood shavings
• switch to no-till or no-till agriculture, to disturb the soil less

• reduce soil compaction caused by livestock and machinery

• manually disturb streetcar lines to reduce soil erosion and runoff
• maintain plant cover to insulate the soil against seasonal and daily warming

You can convert naturally moist topsoil to:

pest control

More soil moisture and surface material can increase slugs, as well as beneficial pest predators. Find out how to control slugs.

How to tell if soil organic matter is increasing

Dig 20cm deep soil pits and look for darker colored topsoil. As organic matter increases, its color becomes similar to that of uncultivated topsoil, such as nearby hedgerow embankments.

There will be more earthworms in the soil. Read a fact sheet on how to count earthworms.

You will also see:

• deeper root penetration, especially through finer roots
• visible pores or spaces in most soil blocks or aggregates
• looser, grainier soil consistency with no visible compaction layer

You will be:

• notice less surface water runoff and soil lost from your fields during heavy rains
• be able to work and use machinery on your land for longer periods of time without damaging the ground
• use less water withdrawn from natural sources for irrigation during prolonged dry periods
• record higher than average levels of organic matter for your soil type and clay level

Soil organic matter (SOM) is the fraction of soil composed of decomposed plant and animal tissues to varying degrees, and is essential for soil health.

It contributes to a range of important soil properties and processes, including water infiltration, soil aeration, water-holding capacity, nutrient cycling, and disease and pest suppression.

Soil organic matter is one of the most important properties of soil to support healthy crops.

The significant declines in SOM observed over the past three decades are of concern for agriculture in the Fraser Valley, including the delta.

These SOM declines were recently identified in an analysis that was part of our five-year research project in partnership with the University of British Columbia (UBC) that assessed the impact of grassland fallowing on various soil properties and crop yields.

One component of the study included a Fraser Valley survey of changes in soil organic carbon (SOC) conducted by Dr. Siddhartho Paul (https://sal-lab.landfood.ubc.ca/ )

Soil organic carbon is an indicator of soil quality and a measure of SOM.

Study results showed large declines in SOC in some areas of the Fraser Valley.

Across the entire Delta agricultural landscape, 93% of the area experienced a decline in SOM from 1984 to 2018.

For fields cultivated annually, the average SOC has decreased by approximately 42% over the three decades, with the current median SOC being equal to 23.14 g C/kg soil (2.3%).

The decline in SOM is important to address and will become even more so as extreme weather conditions become more common due to climate change in the years to come.

Common practices used to increase SOM include incorporating crop residues, animal manures and compost; planting cover crops; crop rotations including in particular perennial grasses and legumes; and reducing tillage practices.

The Delta Farmland and Wildlife Trust supports many of these practices through our stewardship programs.

Further research is currently being conducted by UBC to assess the impact of practices such as winter cover crops and grassland fallowing on SOM.

This article originally appeared in the DFWT Winter 2021 Newsletter and was contributed to the Delta Optimist.

WACO, TX- A new way to analyze the chemical makeup of soil organic matter will help scientists predict how soils store carbon — and how soil carbon may affect climate in the future, says a Baylor University researcher .

A study by scientists from Iowa State University and Baylor University, published in the academic journal nature geoscience, used an archive of soil data from a wide range of environments across North America – including tundra, tropical rainforests, deserts and grasslands – to find patterns to better understand the formation of soil organic matter, which is mainly composed of residues left by dead plants and micro-organisms.

The researchers analyzed samples of 42 soils from the archives of the National Ecological Observatory Network and samples taken from other sites, representing all major soil types on the continent.

The soils were analyzed by William C. Hockaday, Ph.D., Associate Professor of Geosciences at Baylor University, and Visiting Scholar Chenglong Ye, Postdoctoral Researcher at Nanjing Agricultural University, Baylor Molecular Biogeochemistry Laboratory. They used a technique called nuclear magnetic resonance spectroscopy, which allowed them to analyze the chemical structure and composition of natural organic molecules in the soil.

“Soils are a foundation of society by providing food, clean water and clean air,” Hockaday said. “Soils also play a major role in climate change as one of the largest carbon reservoirs on the planet. Even so, the chemical composition of this carbon has been debated by scientists for over 100 years. »

“With this study, we wanted to answer the questions of whether organic matter is chemically similar across environments or varies in predictable ways across environments,” said study lead author Steven Hall, Ph.D. and Assistant Professor of Ecology, Evolution, and Organismal Biology at Iowa State.

The study revealed patterns in soil organic matter chemistry that held true across climates. Understanding these patterns, or rules for how and why organic matter forms and persists in soil, will help scientists predict how soils in various ecosystems store carbon. Carbon can contribute to climate change when released from the soil into the atmosphere as a greenhouse gas. A better understanding of the types of soil carbon existing in different environments can paint a clearer picture of how soil carbon can affect climate and how future climate change can affect the soil carbon pool, the researchers said. .

“This study brought together a strong team of scientists, and for me it was the first time looking at chemical patterns on a continental scale,” Hockaday said. “It’s exciting and rewarding when you inform a long-standing debate and offer an explanation of a major pattern that exists in nature.”

A new way to analyze the chemical makeup of soil organic matter will help scientists predict how soils store carbon and how soil carbon could affect climate in the future, according to a Baylor University researcher.

A study by scientists from Iowa State University and Baylor University, published in the academic journal nature geoscience, used an archive of soil data from a wide range of environments across North America – including tundra, tropical rainforests, deserts and grasslands – to find patterns to better understand the formation of soil organic matter, which is mainly composed of residues left by dead plants and micro-organisms.

The researchers analyzed samples of 42 soils from the archives of the National Ecological Observatory Network and samples taken from other sites, representing all major soil types on the continent.

The soils were analyzed by William C. Hockaday, Ph.D., associate professor of geosciences at Baylor University, and visiting researcher Chenglong Ye, postdoctoral researcher at Nanjing Agricultural University, at the Baylor Molecular Biogeochemistry Laboratory . They used a technique called nuclear magnetic resonance spectroscopy, which allowed them to analyze the chemical structure and composition of natural organic molecules in the soil.

“Soils are a foundation of society by providing food, clean water and clean air,” Hockaday said. “Soils also play a major role in climate change as one of the greatest carbon reservoirs on the planet. Even so, the chemical composition of this carbon has been debated by scientists for over 100 years.”

“With this study, we wanted to answer the questions of whether organic matter is chemically similar across environments or varies in predictable ways across environments,” said study lead author Steven Hall, Ph.D. and Assistant Professor of Ecology, Evolution, and Organismal Biology at Iowa State.

The study revealed patterns in soil organic matter chemistry that held true across climates. Understanding these patterns, or rules for how and why organic matter forms and persists in soil, will help scientists predict how soils in various ecosystems store carbon. Carbon can contribute to climate change when released from the soil into the atmosphere as a greenhouse gas. A better understanding of the types of soil carbon existing in different environments can paint a clearer picture of how soil carbon can affect climate and how future climate change can affect the soil carbon pool, the researchers said. .

“This study brought together a strong team of scientists, and for me it was the first time looking at chemical patterns on a continental scale,” Hockaday said. “It’s exciting and rewarding when you inform a long-standing debate and offer an explanation of a major pattern that exists in nature.”

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A study by scientists from Iowa State University and Baylor University, published in the academic journal nature geoscienceused an archive of soil data from a wide range of environments across North America – including tundra, tropical rainforests, deserts and grasslands – to find patterns to better understand the formation of soil organic matter, which is mainly composed of residues left by dead plants and micro-organisms.

The researchers analyzed samples of 42 soils from the archives of the National Ecological Observatory Network and samples taken from other sites, representing all the major soil types on the continent.

The soils were analyzed by William C. Hockaday, Ph.D., associate professor of geosciences at Baylor University, and visiting researcher Chenglong Ye, postdoctoral researcher at Nanjing Agricultural University, at the Baylor Molecular Biogeochemistry Laboratory . They used a technique called nuclear magnetic resonance spectroscopy, which allowed them to analyze the chemical structure and composition of natural organic molecules in the soil.

“Soils are a foundation of society by providing food, clean water and clean air,” Hockaday said. “Soils also play a major role in climate change as one of the greatest carbon reservoirs on the planet. Even so, the chemical composition of this carbon has been debated by scientists for over 100 years.”

“With this study, we wanted to answer the questions of whether organic matter is chemically similar across environments or varies in predictable ways across environments,” said study lead author Steven Hall, Ph.D. and Assistant Professor of Ecology, Evolution, and Organismal Biology at Iowa State.

The study revealed patterns in soil organic matter chemistry that held true across climates. Understanding these patterns, or rules for how and why organic matter forms and persists in soil, will help scientists predict how soils in various ecosystems store carbon. Carbon can contribute to climate change when released from the soil into the atmosphere as a greenhouse gas. A better understanding of the types of soil carbon existing in different environments can paint a clearer picture of how soil carbon can affect climate and how future climate change can affect the soil carbon pool, the researchers said. .

“This study brought together a strong team of scientists, and for me it was the first time looking at chemical patterns on a continental scale,” Hockaday said. “It’s exciting and rewarding when you inform a long-standing debate and offer an explanation of a major pattern that exists in nature.”

Source of the story:

Material provided by Baylor University. Note: Content may be edited for style and length.

AMES, Iowa – A new study by scientists at Iowa State University sheds light on the mystery of how soil organic matter forms in a wide range of ecosystems.

The study, published in the academic journal Nature Geoscience, drew on archives of soil data from across North America to find patterns in the chemical composition of organic matter. The analysis will help scientists understand the “rules” that govern the formation of soil organic matter and better predict the composition of soils, said Steven Hall, lead author and assistant professor of ecology, evolution and biology of organisms.

Soil organic matter is the organic component of soils, mainly composed of residues left by dead plants and microorganisms. Understanding how soils break down or retain organic matter is important because organic matter plays a central role in the type of services soils can provide, such as whether they make good agricultural soils or whether they can sequester carbon to slow climate change.

“If you pick up dirt and it’s dark in color, a lot of people would say it’s because of organic matter,” Hall said. “But what it really is has been debated for more than 100 years. With this study, we wanted to answer the questions of whether organic matter is chemically similar in all environments or whether it varies from predictably from one environment to another.

To answer these questions, the researchers turned to the National Ecological Observatory Network, which has compiled archives of various soil types from a wide range of environments in North America. These samples included soils taken from the tundra, tropical rainforests, deserts, grasslands and beyond. They supplemented the data with soil samples taken from other sites. These soils underwent a technique called nuclear magnetic resonance spectroscopy in the laboratories of Baylor University. The technique allowed researchers to analyze the chemistry of carbon atoms in the soil.

The results that emerged from the analysis revealed patterns that held true for soils across climates.

“Perhaps the most robust finding is that there seem to be really consistent trade-offs in the chemistry of organic matter,” Hall said. “If you have more of certain compounds, those samples always contain less of other compounds.”

For example, Hall said researchers looked closely at lignin, a compound in many plants that is a key component of wood. The study found that lignin-rich soils generally contained less protein, and vice versa. They also found patterns that appear to match climate and mineral content, Hall said.

Understanding these patterns, or the rules for how and why organic matter forms and persists in soil, will help scientists predict how soils in various ecosystems store carbon, Hall said. Carbon can contribute to climate change when released from the soil into the atmosphere as a greenhouse gas. But a better understanding of the types of soil carbon that exist in different environments can paint a clearer picture of how soil carbon may affect climate in the future, and vice versa.

“The idea is to give us a conceptual model to predict differences in organic matter between ecosystems and understand why that organic matter might be present,” Hall said.

Steven Hall is dedicated to exploring how farmers can get the most out of their soil.

Hall, an assistant professor in the Department of Ecology, Evolution, and Organismal Biology at Iowa State University, runs a biogeochemistry lab where students examine the various factors that can affect soil health.

“Our group is focused on both basic research related to soil organic matter and nutrient cycling in a wide range of ecosystem types,” Hall said, adding that the group is also involved in “applications specific of these ideas to agricultural systems”.

He said the lab is made up of graduate students, postdoctoral researchers, professional scientists and undergraduate students.

One of Hall’s studies in November 2019 explored the impact of cover crops and grassland plants on microbial activity in soil.

He and visiting doctoral student Chenglong Ye from Nanjing Agricultural University in China published results that show that cover crops may not provide the high level of carbon sequestration benefits expected.

“Systems with cover crops or perennials generally increase the total amount of plant residue inputs compared to typical cereal cropping systems, but in some cases their presence can also increase organic matter decomposition rates. “Hall said.

“That is, residue management and nutrient availability can play a key role in controlling carbon gains and losses in these systems. Where nitrogen becomes limiting, microbes can actually “pull” it out of soil organic matter, helping to increase decomposition rates.

Hall stressed that this shouldn’t make cover crops any less attractive to farmers interested in the practice. He noted that microbial activity in these cover crops can provide benefits to soil fertility and reduce the loss of other nutrients.

The lab has three themes posted on its website, and Hall said the items they address are largely influenced by student and researcher interest. One of the themes — “what factors control the persistence and microbial transformations of soil organic matter?” – has been one of Hall’s interests since his thesis.

“We have a collaborative project with the Iowa Nutrient Research and Education Council that focuses on evaluating the environmental sustainability and agronomic impacts of a new microbial nitrogen fertilization technology produced by California-based startup Pivot Bio,” said Hall said.

Other themes focus on plant microbial interactions in the rhizosphere and the impact of nutrient cycling on greenhouse gas emissions.

He said these are complex topics, but lab researchers have found that there is a strong correlation between the rate of nitrogen fertilizer applied and the physical and biological conditions of the soil in controlling these emissions.

“All other things being equal, we would expect higher nitrous oxide emissions where nitrogen fertilizer rates are high and soils are moist and warm,” he said. “More importantly, as nitrogen fertilizer rates increase, nitrous oxide emissions increase exponentially.”

He suggested that to reduce nitrous oxide emissions, farmers could keep nitrogen levels as low as possible “but within the profitable range”.

Through research from the lab, Hall said there are still uncertainties about how tillage practices affect these issues, as well as how the form of nitrogen and cover crops can affect the nitrous oxide.

By Anna Cates, State Soil Health Specialist

One of the benefits of increasing soil organic matter is storing more water in your soil. Why does this happen? Because the organic matter in the soil creates pores of different sizes. However, the exact amount of water stored due to soil organic matter will depend on the texture of the soil.

Soil organic matter is a loaded mix of materials – fragments of last year’s stems and roots, earthworm casts, and living microbes and invertebrates, to name a few. These materials are broken down by physical and biological processes. For example, freezing and thawing cause plant residues to lose their structure. Tiny dissolved molecules flow deep into the ground with rainwater. Hungry invertebrates, fungi, and bacteria consume complex living and dead organic matter and excrete nutrients they don’t need in a smaller, simpler form. These small organic molecules can stick to clay surfaces. Clay surfaces covered with organic matter grow like snowballs and soil aggregates are formed.

How Soil Aggregates Affect Soil Water

Soil aggregates are essential for retaining water in the soil for two reasons. First, a well-aggregated soil has large pores between aggregates to allow water to enter the soil profile. Second, small pores in the aggregates hold water firmly enough to hold it, but loose enough for plant roots to absorb it. It is essential that the soil allows water to drain away and retains water for later. If your soil does not allow water to infiltrate, you will have puddles, runoff and soil loss, and a decreased water supply for plants. If your soil does not retain water, plants suffer from drought.

Thus, soil organic matter is essential for forming aggregates, and aggregates are essential for retaining water. Because of this link, there is definitely a positive relationship between organic matter and water-holding capacity. The increase in water holding capacity depends on your soil type.

Water capacity available to the plant

We are primarily interested in soil water as it relates to the water available to plants. The water capacity available to plants is the water held by the soil against the pull of gravity (i.e. it does not pass through) but not so tight that plants can l aspire. organic matter in coarse-textured soils than finer silts or clays. This is because coarse soils naturally have larger pores between particles and really need organic matter to develop small pores. Fine-textured soils already have small pores and aggregate more easily, so there are diminishing returns on increasing organic matter. More soil organic matter means more soil pores and lower bulk density. Some of these pores are large, which is great for infiltration, but will not increase the water capacity available to plants.

You can calculate how much extra water holding capacity you could get by increasing organic matter, but the number varies by soil type. For example, a recent compilation of studies found that the available water capacity in medium-textured soil increased by 1.03% with every 1% increase in MO (Minasny and McBratney 2017). If you start with 22% available water capacity (moderate for silt loam according to NRCS), adding 1% MO would get you to 23.03% available water capacity (Table 1).

This article was corrected on April 2, 2020. The original version overestimated gallons gained in available water holding capacity with increasing organic matter. Thanks to the eagle-eyed readers who pointed out the discrepancies.