California Ag Network

Tag: Crop Science Society of Agronomy

  • 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

  • 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)

  • 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.

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