California Ag Network

Tag: Soil Science Society of America

Benefits of Biosolids Spread Across Decades of Research for Plant Nutrient Uptake

For more than four decades, biosolids have been applied to land and studied by researchers for many useful purposes. Biosolids are a product of the wastewater treatment process. Yes, that means sewage. However, the sewage is treated carefully to ensure it has beneficial properties and is not harmful.

Biosolids are produced by separating liquids from the solids in wastewater. The solids are then treated to produce a semisolid that is nutrient rich. Jim Ippolito, a professor at Colorado State University, is an expert on the years of work on biosolids and its benefits. He and a colleague, Ken Barbarick, recently reviewed 45 years of biosolids land application research.

“All of this research occurred in Colorado, which in and of itself is amazing. Most other states don’t have the same level or depth of research history,” Ippolito says. “Regardless, we highlight early work where scientists were using basic soil science knowledge to tackle the use of this product. We also discuss current discoveries where biosolids improve soil health in various ecosystems.”

The research was published in the Journal of Environmental Quality, a publication of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Jim Ippolito (right) and Steve Blecker (left) perform soil sampling in wheat-fallow rotation plots. The plots have received agronomic biosolids applications since 1999. Ippolito’s research highlights the benefits of biosolids land application to raise plants to feed animals, to raise crops to feed people, and to do these things safely. Credit: Jim Ippolito

When and why did the use of biosolids begin? It can be traced back to the United States Clean Water Act of 1972. The act gave the Environmental Protection Agency a mission to govern potential water pollution. Part of this was setting standards for municipalities to meet when cleaning their wastewater prior to discharge. Cleaning wastewater generates biosolids, which also have federal regulations.

“As far as I know, there are no other biosolids review articles that span the timeframe between the creation of the Clean Water Act to present,” he says. “This overarching review article is a one-stop shop for anyone interested in the beneficial reuse of biosolids. Our research highlights the benefits of biosolids land application to raise plants to feed animals, to raise crops to feed people, and to do these things safely.”

Biosolids are visible on top of the soil in this wheat field during hot, dry, and windy conditions. The biosolids were applied about 10 months prior to the photo taken. Applying biosolids has been found to improve the health of the soil in semi-arid grazed rangeland settings to allow plant growth as a source of food for animals like cattle. Credit: Jim Ippolito

Over the years, scientists have found many benefits of biosolids. One is that biosolids can be applied to semi-arid agricultural areas and supply crops, such as wheat and corn, with more of the mineral, zinc. This means that humans and animals can benefit from zinc consumption by eating these crops. This is particularly useful while billions of people across the world do not get enough zinc in their diet.

“Micronutrients, like copper and zinc, found in biosolids actually come from the entire municipal infrastructure, such as copper piping and zinc solder,” Ippolito explains. “They are likely also present because they are necessary nutrients for plants, animals, and humans. Furthermore, we shed these and other elements when we go to the bathroom. They concentrate in biosolids along with copper and zinc from the municipal infrastructure.”

Many cities have their own biosolids recycling systems.

Biosolids have been found to improve the health of the soil in semi-arid grazed rangeland settings to allow plant growth as a source of food for cattle. In the face of a rapidly changing climate, it can make the landscape more resilient. Ippolito says that findings like these are highly valuable because one third of all land in the United States is rangeland or pastureland.

Additionally, biosolids have been tested and found to be useful in other applications, such as when a landscape is recovering from a forest fire or when land has been mined. They provide energy for soil microorganisms which, in turn, improve nutrient cycling that helps plants thrive across landscapes.

“We’ve done a lot of good for the state of Colorado and other similar states in terms of beneficially reusing this product that would otherwise be landfilled,” Ippolito says. “Why throw away something that is beneficial? I’ve essentially modeled my career around ways to use biosolids and other products to improve environmental quality in a sound manner.”

Jim Ippolito gives special thanks to Dr. Ken Barbarick for creating a legacy in Colorado biosolids land application research.

The yellow and green vehicle is a new piece of equipment used to spread biosolids at the Meadow Springs Ranch in Colorado. Biosolids are a product of the wastewater treatment process that are treated to enhance beneficial properties. Credit: Jennifer Ward

October 7, 2022
Getting to the Root of How to Grow Cowpea in Difficult, Dry Conditions

Cowpea is an important crop in many parts of the world, especially sub-Saharan Africa. It is resilient and can grow in areas with little rainfall and low-quality soils. But as hardy as it is, cowpea yields can decrease by drought and low levels of soil phosphorus.

A high-resolution root hair image taken from a cowpea seedling root sample. The image was taken after 14 days of growth on germination papers. Root hairs play important roles in cowpea tolerance to drought and poor soils. Credit: Saba Mohammed

In a recent study, researchers determined cowpea root characteristics that could help the plants grow better in drier, low-phosphorus soils.

“Developing cowpea varieties that can produce optimally under stressful conditions is vital,” says Saba Mohammed, lead author of the study at Ahmadu Bello University in Zaria, Nigeria. “These resilient cowpea varieties can help make more people food and nutrition secure.”

The study was published in Crop Science, a publication of the Crop Science Society of America.

Cowpeas are a key source of calories for millions of people across the world. They are rich in protein and other nutrients. Cowpea plants also have a variety of other uses. They can serve as animal fodder and green manure.

Microbes in cowpea root nodules can increase soil fertility. These microbes make atmospheric nitrogen available to plants in the soil – a process called nitrogen fixation. Nitrogen fixation can be beneficial for farmers who cannot afford nitrogen-based fertilizers.

Most cowpeas production is in semi-arid regions. Harsh environmental conditions and poor soils often hamper yields. “Our work established that certain root characteristics increased the yield of cowpea plants under drought or low soil phosphorus conditions,” says Mohammed.

These root features include longer primary roots and higher numbers of lateral roots emerging from primary roots. Root hairs also play important roles in cowpea tolerance to drought and poor soils.

For example, cowpea plants with longer, denser root hairs had higher yields when grown in low-phosphorus conditions. “That suggests these root hair features play crucial roles in acquiring phosphorus from sub-optimal soils,” says Mohammed.

Scientists have long known that roots are a key part of how plants adapt to difficult environmental conditions. “The root system is half of the whole plant system,” says Mohammed. “Yet, it has been relatively under-explored in finding solutions to farming constraints.”

Root systems have diverse strategies for extracting resources from soil. “For instance, plants with deeper roots produce better than those with shallow roots under limited water conditions,” he says. “On the other hand, those with shallow roots may be more suited to soils with suboptimal nutrients.”

A field experiment on cowpea at the Institute for Agricultural Research in Minjibir Agricultural Research Station, Kano State, Nigeria. Cowpea crops are resilient and can grow in areas with little rainfall and low-quality soils. Credit: Saba Mohammed

That’s because nutrients – like phosphorus – are often concentrated in the top layer of soil.

For cowpea plants growing in dry and nutrient-limited soils, roots need to go deeper and spread wide and shallow.

“Our study shows that we can focus on cowpea varieties with longer taproots for drought tolerance and higher numbers of shallower basal roots to extract soil nutrients,” says Mohammed.

While root architecture can provide valuable information, examining root features of mature plants can be a time-consuming and exhausting process. Mohammed says it is easier and more economical to phenotype roots at the seedling stage.

The study showed that examining roots of cowpea seedlings could help identify root features in mature plants that are beneficial for growth in challenging environments.

“Our goal is to use the study results to breed new cowpea varieties,” says Mohammed. “These new varieties would perform optimally under limited water and low soil phosphorus conditions.”

Many small-scale and subsistence farmers may be unable to afford phosphate fertilizers. The new cowpea varieties Mohammed describes would benefit these farmers tremendously. However, he explains that developing new varieties with desired root features can also be a valuable resource in systems where intensive irrigation and fertilizers are used. These cowpea varieties can help reduce production costs and minimize environmental pollution from excessive fertilizer use.

American Society of Agronomy, Soil Science Society of America, Crop Science Society of America: Collectively, these Societies represent more than 12,000 individual members around the world. Members are researchers and professionals in the areas of growing our world’s food supply while protecting our environment. Together we work toward solutions to advance scientific knowledge in the areas of agronomy, crop science, and soil science.

August 30, 2022
Impacts of Winter Grazing, Integrating Crop-Livestock Systems

Winter grazing is part of what is called an integrated crop-livestock system. It is a process where livestock, such as cattle or goats, are allowed to graze a crop field during the winter. It is more common in climates with mild winters. Rather than eating the cash crop the farmer sells, the livestock eat the cover crop that was planted to grow over the winter.

Winter grazing is a useful option for farmers who also raise livestock. They can feed them using cover crops they were going to plant anyway, a cost-efficient and sustainable practice. But how does winter grazing impact the soil underneath? Hayley Crowell, researcher at Auburn University, and her team worked to find out.

Researcher Hayley Crowell collects cotton root samples to be evaluated for fungi colonization rates. These measurements will help the team evaluate the soil health of the integrated crop-livestock system. Credit: Audrey Gamble

“Finding the best management practices to improve soil health and maximize economic gains can improve the livelihoods of producers in the Southeast and all over the world,” she explains. “This is possible by using cropland year-round and potentially improving crop productivity through increased soil health.”

This study was published in Agrosystems, Geosciences & Environment Journal, a publication of the American Society of Agronomy, and Crop Science Society of America.

They performed a study for two years on a site in Alabama. The team started the experiment in October 2018 beginning with planting the cover crops. The grazing began and then the first cash crop of the experiment was planted in the spring. The cash crop was harvested in mid-October. Next, the cover crops were planted shortly after harvest.

In mid-January after the cover crop was well-established, they allowed livestock to graze the fields until it was time to plant more cash crops in the spring and repeat the process. In their experiment, they let cattle graze the fields for different lengths of time and studied the soil carefully. “Soil chemical properties are very important to understanding and evaluating soil health,” Crowell says. “Various soil chemical indicators are related to basic soil functions. These include promoting microbial activity, controlling water flow, nutrient cycling, and physical stability.”

They tested for soil organic carbon and active carbon to check for impacts on soil organic matter, which is viewed by most as very important for soil health. The team also analyzed what is called water stable aggregates and penetration resistance. These are qualities of soil that impact how it takes in water and how well plants grow in it. Lastly, they studied the microbes in the soil, many of which are beneficial to plants.

Rows of cotton, a cash crop, grow among bits of cover crop left on the soil surface. Cover crops are plants grown during the off-season. Credit: Hayley Crowell

After the first two years of their study, the scientists did not find that winter grazing impacted the soil very much. This means there were no positive effects. However, it also means there were no negative effects. This is useful information for farmers practicing winter grazing.

“Our data points to how farmers can use this style of management without seeing a big change in soil health in the first two years,” Crowell says. “The study was only based on data from two years. So, it’s not too surprising that our data didn’t point to significant changes in soil health between the different grazing treatments. With more time, we will hopefully be able to paint a clearer picture of how the length of winter grazing impacts soil health.”

Crowell stresses that this is part of a long-term study, and will require further research collecting more data on the impacts of winter grazing on soil. It is possible cattle hooves stepping on the soil will compact it, or that their manure will provide benefits to the soil. These are just a couple of possibilities that will be examined in future work.

“There is limited research on integrated crop-livestock systems that are designed to promote soil health,” she says. “While some producers are already incorporating winter grazing into their cropping system, they are not necessarily managing it in a way to improve soil health. This is what our study aimed to investigate.”

Funding for this research was provided by the Alabama Natural Resources Conservation Service.

August 22, 2022
How Young Soil Supports Plant Life with Naturally Occurring Fungus

In order to grow well, plants need a place to grow, access to nutrients, and in most cases sunlight. A rich soil provides that home and a good supply of nutrients. But young soils have less to offer – yes, soils can have different ages ranging from hundreds, to thousands, to millions of years old. According to soil scientist and Soil Science Society of America’s (SSSA) blogger Madhav Dhakal, soil is being made and lost all the time, with various dynamic processes.

The process of soil formation is often given the acronym ClORPT for: climate, organisms, relief, parent material and time. Soils in warmer climates tend to be older than ones in colder climates. Many organisms, like microbes or insects, help aid soil formation. The term “relief” refers to the topography area. So, usually soil at the bottom of a mountain range – exposed to less erosion and warmer weather, will be older than soil at the top of a mountain.

The major parent material for soils are rocks. Soil formation takes place after a gradual exposure of rocks to the elements and activity of organism – called weathering.

One important thing to consider during this whole transformation is time. Time is relatively long for the formation of soil. It happens over geologic time – or millions of years. Over these long periods, landscapes and soils are continuously transforming from one form to another. With time, soil forms different horizons or layers, parallel to the earth’s surface.

However, soils of recent origin may not contain a distinct horizons or formations. For example, Entisol and Inceptisol are among the 12 soil orders in the U.S. Soil Taxonomy that contain no or very weak horizons or layers of soil.

In addition to the variety and ages of soils as a home for plants, plants themselves have different types of adaptability. For millions of years, the plant kingdom endured several catastrophic events, geological changes, and climatic extremes. Plants were able to adopt to incredibly different types of surfaces or soil, where the soil itself is highly dynamic and changeable.

The versatility of plant species may have allowed them to survive in extreme conditions such as hostile climate, rocky, acidic, and salty surfaces.

There are nearly 435,000 unique land-dwelling species of plants in the world. Some of them grow with very little ingredients or even without sufficient water. For example, some cactus species thrive in the desert. Similarly, lithophytes can grow either on the surface of rocks or in crevices.

What is it about some plants that allows them to grow in unfavorable conditions? There are a few things. Rock felt ferns, orchids, and liverworts can grow on a rocky substrate, with different tactics or physiological adaptation. They are even capable of feeding off the nutrients from rainwater and nearby decomposed plants, including their own dead cells.

Lithophytes are a type of plant that grows well on rock surfaces. For most of the lithophytes, the nutrient nitrogen is available from the atmosphere in the form of ammonia. Lithophytes have a smaller number of root hairs and larger root diameters compared to common plant species. This makes them able to efficiently absorb nutrients.

Lithophytes are a type of plant that grows well on rock surfaces. For most of the lithophytes, the nutrient nitrogen is available from the atmosphere in the form of ammonia. Lithophytes have a smaller number of root hairs and larger root diameters compared to common plant species. Provided by Madhav Dhakal

Other plants have developed cooperative relationships with soil microbes, which may help them survive in younger soils. Cacti can metabolize a type of acid that helps them with photosynthesis. Plants like peas are legumes – and can work with a bacterium in the category of Rhizobium, and this helps them acquire nitrogen.

Newly formed soils, such as Entisols and Inceptisols can support plant that have these built-in strategies to supplement their essential nutrients. Depending on the parent material, these soils can provide mineral nutrients such as nitrogen, phosphorus, potassium, as well as micronutrients like calcium, iron, zinc, boron, etc.

Indeed, as adaptable plants colonize these soils, they also start to help build more soil, in conjunction with microbial and insect activity. Their dead roots and waste products become organic matter, building up the soil bit by bit. One example of how plants can improve soils is the plant lupine (Lupinus Lepidus). Lupine’s metabolites can neutralize acids produced by volcanic emanations. This makes the soil more habitable by other types of plants that cannot survive in acidic soils. There are hundreds of plant species that can survive on and improve young soils over time.

The Soil Science Society of America (SSSA) is a progressive international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, and founded in 1936, SSSA is the professional home for 6,000+ members and 1,000+ certified professionals dedicated to advancing the field of soil science. The Society provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

August 22, 2022
Pumpkin Production can Benefit from Conservation Practices

Pumpkins (Cucurbita pepo) are a common vegetable crop sold at local pumpkin patches and farmers markets, in addition to commercial production. In 2019, the value of harvested pumpkin was worth $180 million.

In addition to the value of harvested pumpkins for commercial use (canned pumpkin, produce departments, etc.) pumpkins are also a staple crop in agritourism operations. In Kansas alone, there were 409 farms registered in the state in 2020. Agritourism enterprises have shown to benefit communities by connecting consumers with agriculture and help preserve farmland in rural and peri-urban areas.

Vegetable crop production typically involves smaller acreages than agronomic production. However, farmers often rely on intensive cultivation of soil to prepare the seedbed for planting. Tilling also helps manage weeds.

Agritourism enterprises have shown to benefit communities by connecting consumers with agriculture and help preserve farmland in rural and peri-urban communities. Shown here, a pumpkin patch where people can pick their own pumpkin as part of fall activities. Credit: Canva Pro

Over time, extensive tillage can have negative effects on soil structure and microbial properties. Researchers in Kansas recently published a paper studying conservation practices for pumpkin production. The research was published in Soil Science Society of America Journal, a publication of the Soil Science Society of America.

According to researcher Peter Tomlinson, “no-till production methods have been widely adopted by agronomic (field corn, soybean, wheat, etc.) growers throughout the United States. However, no-till practices for vegetable production in the Central United States are relatively rare. Mid-Atlantic States such as Pennsylvania, Virginia, and Maryland have adopted no-till practices for pumpkin and other large-seeded vegetable crops.”

The study compared growing pumpkins in a biannual tilled control system with annual tilled systems that used cover crops. “This project is designed to compare systems, rather than individual effects of cover crops or tillage,” says Tomlinson. The authors reported the effects of a three-year project on dynamic soil properties.

The annual systems used cover crops planted into the soil. They were terminated before planting the pumpkins. The team researched cereal rye and oat alone, as well as cereal rye with other cover crops mixed in. They performed the study over three growing seasons at two sites – Eastern and South-Central Kansas. Both sites have humid climates with warm summers, and loam-type soils.

A field planted with pumpkins grown in a cover crop system with cereal rye. Cover crops have proven environmental benefits, though many vegetable growers in the Midwest have been slower to adopt this conservation practice. A recent study showed soil health benefits with no reduction in yield. Credit: DeAnn R. Presley

At each of the study sites, soil health was assessed at two key times; plots were sampled 2-3 weeks after pumpkin planting, and immediately after pumpkin harvest.

The main soil physical property that was affected by management systems used in this study was an improvement with the use of conservation systems in total soil aggregation and the presence of very large aggregates. Soil aggregates are small particles of soil held together with a glue-like substance. This is usually due to microbial activity. Soil aggregates help in the stability of the soil making it less prone to wind and water erosion.

“Adding cover crops and reducing tillage in a pumpkin production system can cause a measurable change in soil aggregation in a short period of time, two years in this study,” says Tomlinson.

“There were few instances where the species or mixture of species influenced the results,” he continues. “Rather, the presence of cover crops in the conservation systems appears to have a more dominant role. The significance of this work is that it demonstrated there can be measurable changes in some dynamic soil properties in the short term (two years). This is within a system that involves a reduction in tillage operations and the addition of cover crops.”

“We conclude that the use of less tillage and a cover crop in a conservation system is generally beneficial as compared to a conventional system. This study illustrates the potential for improving some soil health parameters in as little as two years,” says Tomlinson. Future research will focus on how the implementation of conservation system across a range of agricultural systems and time scales effect dynamic soil properties.”

Funding for this research was provided by NRCS Conservation Innovation Grant.

Cathryn Davis measuring infiltration rates in an oat cover crop during her MS research published in this paper (photo by DeAnn R. Presley)

April 15, 2022
Getting a Solid Soil Response to Biosolids Application in Ag

Many people do not know that human waste can be recycled to benefit the environment. After intense treatment, it can be applied to fields in the form of biosolids.

While scientists know that this can benefit the soil, they are still learning about the best ways to measure this. In addition, it can be hard to determine how much it helps the soil over a long period.

That’s where Yocelyn Villa from the University of California, Merced comes in. She and her collaborators studied fields in California where biosolids have been applied for 20 years.

Their findings were recently published in Journal of Environmental Quality, a publication of the American Society of Agronomy, Crop Science Society of America and the Soil Science Society of America.

“Our goal was to assess how stocks of soil carbon have changed over time at each of these sites,” she says. “We did this by measuring how much carbon is present compared to adjacent areas without biosolids application. Specifically, we wanted to account for not only shallow soil depths, but also deep soil carbon, down to 100 cm depths.”

The three sites they studied had different biosolids application frequencies, management practices, and soil texture. The researchers focused on measuring microbial biomass carbon and nitrogen, soil organic carbon, and total nitrogen. These are all soil qualities known to benefit from the application of biosolids.

They predicted that the more biosolids that are applied, the more carbon and nitrogen there would be in those soils. Most of their results were what they expected. However, they were surprised that the site that had the highest application of biosolids did not show the most change. In addition, one of the sites did not show a benefit from the biosolids application until they performed tests on the deeper soil.

Soil sample were taken using an auger at five different depth increments (Photo by Rebecca Ryals).

“If we had only taken the top 30 cm into account, we would have not detected a change in soil carbon at the Merced site,” Villa said. “This is the biggest and most important finding.”

She adds that this shows how the organic matter in biosolids does not simply sit in the soil and accumulate. Instead, it is impacted by dynamic properties that also influence soil organic matter.

This told the researchers that it’s important to measure deep soil carbon and consider other management practices at a site when studying the impact of biosolids. These local controls can be soil texture, irrigation practices, and tillage.

“Many studies have shown the benefits of biosolids application for plant production and nutrient cycling,” Villa explains. “This conjointly provides benefits to soil carbon. Farmers and ranchers have seen differences in vegetation for livestock and other soil health benefits. I would recommend monitoring these benefits through time.”

Different areas were roped off to create transects. Along each transect, soil samples were taken every 10 meters (Photo by Rebecca Ryals).

Another reason scientists are interested in soil carbon is because of its potential to mitigate climate change. Soils that can sequester carbon can keep it out of the atmosphere. So, Villa’s findings highlight the importance of taking deep soil carbon into account to better predict a soil’s ability to mitigate climate change.

“This research is interesting to me personally because I have always been interested in climate change,” she says. “The more I learned about the environment, the more I realized that soils may be the key to mitigate climate change.”

The next steps in Villa’s work are to determine how exactly the soils stabilize carbon and keep it in the soil. She is also assessing where the carbon is in the soil, which will provide insight on how accessible the carbon is for microbes to use. Overall, she is excited to see others beginning to appreciate soil’s potential.

Biosolids have been used in cities like Chicago for several years, to help clean up industrial sites and other purposes.

“I think people don’t realize that human waste can be recycled like this, and that soil is a potential solution to climate change,” she says. “It’s always a treat to see how people’s faces light up with intrigue. Hopefully I have convinced them that we need to stop treating soil like dirt!”

Funding for this research was provided by the Bay Area Clean Water Agencies, Jena and Michael King Foundation, and Department of Life and Environmental Sciences at the University of California, Merced.

Biosolids are applied using a spreader in agricultural soils. All biosolids applied in the study had similar nutrient composition (Photo by Rebecca Ryals).

American Society of Agronomy, Soil Science Society of America, Crop Science Society of America: Collectively, these Societies represent more than 12,000 individual members around the world. Members are researchers and professionals in the areas of growing our world’s food supply while protecting our environment. Together we work toward solutions to advance scientific knowledge in the areas of agronomy, crop science, and soil science.

Twitter: @ASA_CSSA_SSSA & @SSSA_soils | Facebook: ASA, CSSA & SSSA | Instagram: @sustainablefoodsupply & @iheartsoil

December 17, 2021
Measuring Soil Health Easily and Reliably

Healthy soils are a precious resource. They are vital for protecting ecosystems, maintaining water quality, producing crops, and mitigating climate change.

There are numerous indicators to measure soil health. However, these indicators don’t always provide consistent results. In a new study, researchers report evaluating a rapid and inexpensive indicator of soil health, especially for dryland farming.

This study was recently published in the Soil Science Society of America Journal, a publication of the Soil Science Society of America.

The researchers measured bursts of carbon dioxide gas emitted when dried soil samples are rewetted. These bursts of carbon dioxide – called carbon dioxide flush – are an indicator of soil microbial activity.

“Measuring carbon dioxide flush is simple and inexpensive,” says Upendra Sainju, lead author of the study. “We also found that carbon dioxide flush is related to several soil properties and long-term crop yields.”

Measurement of carbon dioxide flush in one-day incubation following rewetting of dry soil in a glass jar. The carbon dioxide flush is absorbed by an infrared analyzer attached to the cover of the jar (inset, upper left) and read in a laptop computer downloaded with the appropriate software. Credit: Upendra Sainju

Sainju believes carbon dioxide flush can be used to measure soil health and relate crop yields reliably. Currently, this method is evaluating to estimate dryland crop yields in arid and semiarid regions.

There are several advantages to using carbon dioxide flush as an indicator of soil health. For one, no chemicals are needed. Researchers can measure carbon dioxide flush from soil samples using devices called infrared analyzers.

“Not needing chemicals means carbon dioxide flush can easily be used to measure soil health directly from the field,” says Sainju. “No chemicals being used also makes this process quick and economical.”

That’s important because several existing ways to measure soil health can be expensive and take a long time to analyze. Also, “they provide mixed results when measuring soil health,” says Sainju. Having a single reliable measure of soil health will help farmers, ecologists, policy makers and various other stakeholders to evaluate the sustainability of agroecosystems for crop production, according to Sainju.

In addition to measuring soil health, measuring carbon dioxide flush can also help farmers reduce nitrogen fertilizer use. “We can use carbon dioxide flush to estimate how much nitrogen will be available from the soil to crops during a growing season,” says Sainju. That means farmers can be strategic with fertilizer use. That can lead to lower costs of farming while enhancing environmental benefits.

To test carbon dioxide flush as a soil health indicator, the researchers collected soil samples from two dryland study sites, both in northeastern Montana. For each soil sample, Sainju and colleagues measured carbon dioxide flush in two different ways.

One was the traditional way – add water to air-dried soil samples and let them sit for four days. Then the researchers used chemicals to measure carbon dioxide flush.

They also tested a faster method; one where the wetted soils sat for just one day. Then, the researchers used an infrared gas analyzer to detect the carbon dioxide flush from the samples.

These two methods yielded slightly different carbon dioxide flush results.

Soil sample, water, container, glass jar, and cover with the infrared analyzer used to measure the carbon dioxide flush. After wetting the soil sample, it will be placed in the mason jar for one day. A carbon dioxide detector is under the lid, and information will be fed into a computer for data collection. Credit: Upendra Sainju

So, Sainju and colleagues tested a whole lot of soil properties – physical, chemical, and biological – and matched them with the two sets of carbon dioxide flush results. “Our results showed that the one-day results were better related to soil properties and crop yields than the four-day incubations,” says Sainju. That meant the easier and faster method of measuring carbon dioxide flush also resulted in a more reliable, inexpensive, and useful indicator of soil health.

Sainju and colleagues plan to test this method in short-term experiments under dryland and irrigated cropping systems next. They will also expand testing the method in various soil and climatic conditions in different regions of the country.

Testing of carbon dioxide flush as a predictor of long-term mean crop yields is especially important, according to the study authors. That’s because non-soil factors – such as droughts and floods, or pests – can affect crop production dramatically in some years. In the meantime, “measuring carbon dioxide flush provides soil health results that are accurate and reliable,” says Sainju. – Article originally published by the Soil Science Society of America

October 21, 2021
What is “soil carbon”?

You may have heard a lot about soil carbon, “storing” carbon in soil, or “carbon markets.” So, let’s look at the relationship between soil and carbon in basic terms.

First, carbon. It’s the sixth element on the periodic chart. In nature, only two things are pure carbon: diamonds and graphite. However, carbon can interact with other elements to form compounds that are all around us every day.

One common carbon-containing compound that is frequently in the news is carbon dioxide. Carbon dioxide is the gas that humans breathe out, after we inhale air containing oxygen. It’s a natural product of our metabolism, it’s made by all other animals when they breathe, and it’s even made by some soil microbes during their metabolism.

Carbon is the 6th element and easily bonds with other elements. Carbon is stored in the soil as part of organic matter as well as frozen carbon dioxide in colder climates like the Arctic.

Carbon dioxide is a natural compound in air, but with the advent of the industrial revolution, much more of the gas has been put into the air. Carbon dioxide is made by many manufacturing processes, and it is also produced when we use certain types of fuels – like coal and gas – for energy. The machines that produce items like appliances, cars, and all the things we buy are also responsible for pushing more carbon dioxide into the air.

When carbon dioxide is in the atmosphere, it traps in heat around the earth. That’s why carbon dioxide is called a “greenhouse gas,” It acts like the glass ceiling of a greenhouse to trap heat. The more carbon dioxide in the air, the higher the earth’s surface temperature will be.

In addition to being in the air, carbon compounds can be found in soil. One form of “soil carbon” is composed of carbon dioxide, which is found in abundance in the frozen ground of the tundra.

Another very important type of “soil carbon” is organic matter, which is made of decayed materials from living things like plants, animals and microbes. How does organic matter have carbon in it? The term “organic” in chemistry means chemical compounds that contain carbon (and usually hydrogen) along with other elements. Organic compounds are prevalent in nature, especially in living things. You may recall that plants “breathe in” carbon dioxide, and “breathe out” oxygen. Plants use the carbon dioxide to make new cells so stems, roots, and leaves can grow. The carbon part of carbon dioxide, and other elements like nitrogen and oxygen, are even used to make flowers, fruits, nuts, and vegetables.

A feature of healthy soil is a buildup of carbon in the form of organic matter, and even waste of earthworms, insects and other creatures that live in the soil. Even human bodies have organic carbon compounds in them! Humans are mostly made of hydrogen, oxygen, carbon, and nitrogen.

Soils in the Arctic and Subarctic regions store over half of the Earth’s soil carbon. Shown here, a thick organic matter layer of moss, twigs, and roots. They formed under cool, acid, aerobic conditions. Note the dark layer of charcoal at about 30-35 cm. Credit: Chien-Lu Ping, University of Alaska, retired.

The carbon cycle: As plants grow and die, they leave behind sugars and carbohydrates (both contain carbon) in the soil. This is used by soil microbes and other soil life as a food source. This makes a wonderful carbon cycle, with plants pulling carbon from the air in the form of carbon dioxide and storing it in the soil as organic matter for other living things to use.

As long as this carbon cycle stays balanced – either by keeping organic matter quantities stable or increasing – the atmosphere is safe. But when human disrupt this cycle by building cities where forests once were, or other anthropogenic changes, it disrupts the carbon cycle. The carbon that was stored as organic matter can easily be put back into the atmosphere as carbon dioxide. Clearing land for agriculture also made soils lose carbon to the atmosphere.

And, remember that frozen carbon trapped in the frozen tundra? As global warming continues, soil carbon is being lost at faster and faster speeds, as the frozen carbon dioxide thaws. In addition, increases in temperatures of the tundra also increase the activity of soil microbes. As they “eat” more organic matter, this stored carbon is lost.

Keeping as much carbon in soils as possible is important to life on earth. And scientists are researching ways to store more carbon in the soil in the form of organic matter. You can help keep more soil carbon in your yard! Follow these tips to help your plants and the environment. — By Susan Fisk, Soil Science Society of America and Matthew Polizzotto, University of Oregon

October 5, 2021
Measuring Nitrogen in Green Manures (Cover Crops)

A crimson clover plant, which is generally recommended to grow in a mixture of grasses, which was used in this study (photo by Sandra Wayman)

Both chemical fertilizers and cover crops can help build the nitrogen content in soil. But cover crops come with many other benefits, like improving soil structure and boosting beneficial microbes. Researchers at Cornell University are looking at ways to help breed better cover crops, also known as green manures, that could help farmers in their quest to grow crops in the most sustainable way. Their results were published in Crop Science, a publication of the Crop Science Society of America.

Katherine Muller and her team are working on strategies to measure nitrogen fixation in breeding programs for two common cover crops: crimson clover and hairy vetch. Both crops can pull nitrogen from the air to help them grow. This is called nitrogen fixation.

“Green manures are crops used to improve soil fertility,” says Muller. “They help the soil by adding nutrients. We look at legumes, which bring nitrogen into the soil due to their symbiotic relationship with bacteria.”

The use of legume green manures has been around for thousands of years. However, after the 1950s, chemical fertilizers became the main nitrogen source for farmers in developed countries. This is because two scientists, Haber and Bosch, found a way to pull nitrogen from the air, and make chemical fertilizer.

Though this type of fertilizer is productive, it also takes energy to make it – and it can easily slip into water bodies if not managed correctly.

“Cover crops are important ecological management tools,” says Muller. “They foster microbial communities and put nutrients in the soil. Essentially, they help build fertile soil that can supply nutrients when plants need them.”

The use of cover crops can be risky to farmers because they cannot determine the exact amount of nitrogen supplied to the soil. Chemical fertilizers allow for the exact calculation of the amount of nitrogen applied to a crop. But how much nitrogen is provided by each type of cover crop isn’t a known number.

The amount of nitrogen supplied by a legume cover crop depends on how well it grows and how much of its nitrogen comes from fixation versus uptake from soil. Currently, cover crop seeds available do not have selective breeding for nitrogen fixation – a valuable trait.

Plant breeders are working to develop cover crop varieties that reduce the risks and increase benefits to farmers. They hope that better varieties will increase the use of cover crops as an alternative to chemical fertilizer. Nitrogen fixation is one of their top priorities for legume green manures.

“We aim to help plant breeders develop strategies to target nitrogen fixation in cover crops,” explains Muller. “Because nitrogen fixation is a complicated trait that changes as plants grow, the timing of measurements is important.”

A root system of a hairy vetch plant, with nodules that contain a symbiotic nitrogen fixing bacteria (Photo by Katherine Muller).

For farmers, the most important measurement of nitrogen fixation is when the crop is terminated. Legume green manures are usually terminated in the late flowering stage. Earlier termination means the crop is likely to resprout and become a weed. However, breeding programs for hairy vetch and crimson clover cannot take that measurement, as they need to remove the plant before cross-pollination.

“Our team did a field experiment with an active breeding program,” says Muller. “We collected plant tissues and measured nitrogen fixation. We were able to tell how much of the plant’s nitrogen comes from fixation versus the soil.”

The team tested three kinds of samples that a plant breeder may take to compare them to the sample most relevant to farmers. They then measured nitrogen fixation by sending their samples to a lab that measures total nitrogen content and the abundance of a naturally occurring stable isotope.

Nitrogen from soil usually has a higher abundance of the nitrogen stable isotope than nitrogen from fixation. This allows researchers to estimate the proportion of nitrogen a plant obtains from soil versus fixation.

“Our recommendation is to collect stems from each plant in the early flowering stage to measure the nitrogen fixation via stable isotopes,” says Muller. “This provides a good proxy for nitrogen fixation in whole plants, measured in the late flowering stage that is more relevant to farmers.”

According to Muller, if breeders are going to add one measurement, it should be this. The proportion of nitrogen obtained by fixation often does not correlate with plant size or other measurements.

“It is important to measure actual nitrogen fixed in the cover crop because it can vary,” says Muller. “Farmers want to know how much nitrogen they are bringing into their fields. We need to accurately measure and provide this information to help farmers make decisions. We hope our research will encourage more farmers to adopt legumes cover crops as a nitrogen source.”

Katherine Muller is a postdoctoral researcher at Cornell University. This research was done in conjunction with the Legume Cover Crop Breeding Project, funded by the United States Department of Agriculture.

American Society of Agronomy, Soil Science Society of America, Crop Science Society of America: Collectively, these Societies represent more than 12,000 individual members around the world. Members are researchers and professionals in the areas of growing our world’s food supply while protecting our environment. Together we work toward solutions to advance scientific knowledge in the areas of agronomy, crop science, and soil science.

August 16, 2021
How do Nematodes Help Plants and Soils?

Nematodes normally get a bad reputation. Yes, some of these miniscule creatures can cause harm in plants and animals. But little is known about the non-parasitic nematodes, which have many beneficial roles. Ashley Shaw from the University of Oregon explores this topic in this Soils Matter blog:

It might be hard to believe, but you may never have seen the most abundant animal on Earth: soil nematodes! They represent eighty percent of animal life by number and live in nearly every habitat. They are hard-working and important organisms.

Soil-dwelling nematodes, which I research, are tiny – usually between 1/500^th to 1/20^th of an inch! (But there is a nematode that lives inside sperm whales that is nearly thirty feet long.)

Indeed, some of the best-known nematodes are parasites. There are different nematode parasites of plants and animals. That means they live in or on the plant or animal, cannot survive without them, and sometimes kill their host (and then move on). But many more nematodes are free-living. In soils, nematodes live in water films that surround soil particles. Both plant root parasitic and free-living nematodes play an important role in plant health and plant feedback to soil carbon.

Photo of a predatory nematode. Predatory nematodes attack and devour other nematodes. Through their feeding, they keep populations of plant parasites and microbial feeding nematodes in check, optimizing plant growth (Credit: Ashley Shaw).

An incredible variety of soil nematodes exist at all levels of the soil food web. At the base of the food web, some feed on plants and algae, others graze on microbes (bacteria and fungi). At higher levels in the food web, nematodes that are predators and omnivores eat other invertebrates, protists, and even other nematodes. In some cases, “predatory” nematodes are the “good guys,” keeping populations of parasitic nematodes in check.

This food web is important to plant health and soil carbon storage. For example, by feeding on bacteria and fungi, microbial grazing nematodes help return nitrogen to the soil through their waste. This makes the nitrogen available again for plant use, improving plant growth.

Nematodes bring other species into the soil food web, too. Some bacteria survive the nematode gut and are deposited along with nematodes’ waste products. Still more hitch a ride on the outside of nematodes’ bodies. As nematodes move around in soil, they deposit bacteria in new places, spreading them around. The bacteria can contribute to and speed the process of decomposition, returning carbon to the soil for storage.

But most good things have a limit: at very high populations, nematodes that feed on bacteria and fungi can reduce their populations. This can lead to lower decomposition and nutrient turnover rates by bacteria and fungi, even lowering plant growth.

Plant parasitic nematodes attack roots using a piercing tool in their mouth. This “stylet” punctures plant cells so it can suck its carbon-rich juices. Some nematodes release chemicals that cause lesions or tumor-like growths on roots. They drain the plant’s strength above- and belowground.

In small populations, plant parasitic nematodes can stimulate root growth, but in high numbers they destroy roots, stunt aboveground growth, and cause disease. Lower plant growth (of both roots and shoots) leads to lower return of organic material to soil and eventually, lower soil carbon.

While the nematode species responsible for plant diseases have received a lot of attention, far less is known about the non-parasitic part of the soil nematode community, which plays mostly beneficial roles in soil. Ensuring a balance between beneficial and plant parasitic nematode groups is important for plant health and its contributions to soil carbon.

Generally, plant-root parasitic nematodes harm plant growth and microbial-feeding nematodes improve it, but other nematodes are also important. For example, predatory nematodes play an important role in regulating populations of plant-parasitic and microbial-feeding nematodes. Through their feeding, they keep populations of plant parasites and microbial feeding nematodes in check, optimizing plant growth.

However, predatory nematodes are also highly sensitive to environmental changes. Their populations often decline with soil disturbances such as pesticide use, fertilization, tilling, or soil compaction. Situations where soil is heavily managed often leads to very low predator populations and higher populations of harmful groups. Predators are also sensitive to changes in rain and temperature, which can also cause an imbalance toward harmful groups.

Shaw is studying compost additions to rangelands to determine the effects on soil carbon and plant growth. Compost also changes the soil food web – including the numbers and diversity of nematodes.

My current research is examining how active land management practices can help boost beneficial nematode groups in soil by improving soil habitat. We are studying compost additions to rangelands and whether they can improve soil carbon storage and plant growth.

Compost directly provides nutrients and increases soil water retention, improving plant growth. Compost is also changing the soil food web in ways not seen in some of the other treatments in our study plots. We think that the soil organic matter in the compost improves soil habitat for predators, supporting the long and complex soil food webs with abundant predatory nematodes that help keep root parasitic nematode populations in check. The result is that plant disease and root parasitism has declined, leading to greater plant growth and root carbon inputs under compost treatments, which benefits soil carbon storage.

Photo: After collecting soil samples, Shaw and her research group inspect nematodes by extracting them into water and examining them in a dish using a microscope. Shown: a diverse grouping of nematodes (longer, worm-like structures) along with a tardigrade and some small soil debris that made it through the extraction process. Credit: Ashley Shaw

The Soil Science Society of America (SSSA) is a progressive, international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, SSSA is the professional home for 6,000+ members dedicated to advancing the field of soil science. It provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

Follow SSSA on Facebook at SSSA.soils, and Twitter at SSSA_Soils. SSSA has soils information on www.soils.org/about-soils, for teachers at www.soils4teachers.org, and for students through 12^th grade, www.soils4kids.org.

May 17, 2021