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In a new study biochar helps yields, but only in the short term
Adding biochar to a farm's field is an irreversible decision, so understanding its long-term impacts is essential for farmers to make informed decisions.
Biochar, a charcoal created from organic materials burned at high temperatures and added as a soil amendment, has been shown to increase pH and soil fertility in areas with more weathered, acidic soils, like the tropics. But a new study shows its impact on productive soils like those in California's Central Valley may be quite different.
Findings from a four year study conducted at the Russell Ranch Sustainable Agriculture Facility at UC Davis showed an increase in corn yields in the second year after adding biochar, but through different means than have been observed elsewhere.
The study, published in the journal Agriculture, Ecosystems and Environment, used biochar made from walnut shells, cooked at 900°C from an orchard in Winters, Calif. Biochar was added to a plot rotating tomato and corn crops at the Russell Ranch Sustainable Agriculture Facility at UC Davis, a long-term research facility focused on using farm management practices similar to those used at commercial farms.
Short term boosts in yields
“A lot of biochar lab studies look at intricacies of how biochar changes nitrogen cycling, so I was very focused on looking at that in the field,” says Deirdre Griffin, Ph.D. candidate in soils and biogeochemistry at UC Davis and lead author of the study.
But instead of a change in the nitrogen cycle, the biochar affected potassium, phosphorous, and calcium in the soil, causing an 8 percent increase in corn yields. The increase, however, didn't happen until the second year after application.
That delay may be due to biochar's hydrophobic nature — it repels water when first in the ground, and may only start to interact with soil after significant time. After year two, the yield benefits of biochar dropped off, and by year four showed no difference compared to plots without biochar.
“The benefits that we saw were from direct fertilization from biochar, in which case growers might be able to see the same boost in yield if they applied a little more fertilizer,” says Griffin. “We didn't see much change in the soil properties that could have more lasting effects. But those things could still be impacted in the coming years as the biochar continues to age.”
To see continued yield increases like these, growers may need to apply biochar regularly, which is not its intended purpose and may pose challenges for growers. Biochar can be dusty, dispersing black soot as it is applied. Growers can wet biochar to limit its dust, but without overcoming that challenge, repeatedly adding biochar to the soil may limit its appeal.
Many biochars, many functions
Like compost, different biochars act differently in the soil. Different sources (type of shell or other organic material), treated at different temperatures, and added to varying soil types can all impact what benefits a grower may see from biochar.
Carbon sequestration, not included in this study, is broadly understood as a benefit of biochar, and some research is looking at its potential to pull heavy metals from soils.
“When biochar research started flourishing, people started seeing positive results in tropical systems and got excited about it,” says Griffin. “Because of our soils and agriculture, we don't necessarily see the same benefits in our systems. But every biochar is different, and we need to understand their characteristics, to engineer them for different systems and different purposes. And we're still working to understand that.”
Griffin's study is ongoing and Russell Ranch and will continue to provide insights on biochar's impacts over time.
Having a long-term study that uses realistic farm practices will help build the understanding of the role of biochar in already fertile soils, and have strong data showing how biochar really acts in the long run, so farmers making the irreversible decision to add biochar know exactly what they are investing in.
More information on biochar can be found on the UC Division of Agriculture and Natural Resources' Biochar Blog, the Solution Center for Nutrient Management, and the Biochar Database managed by associate professor Sanjai Parikh at UC Davis.
New database captures the benefits of biochar
The origins of interest in biochar, a charcoal-based soil amendment, are almost mythic in nature. In the Amazon Basin, a rainforest region with typically infertile soils, segments of soil have been discovered to be almost black in color and rich in nutrients. The soil’s color is derived from its high organic matter content, believed to originate from historical charcoal applications added to the soil some 2,500 years ago, either intentionally or as a waste product from cooking.
Recently, there has been a growing interest in whether the fertility of these “amazon dark earth soils” can be replicated in modern farming practices, and a new UC Davis database helps users and researchers better understand that replicability.
The charcoal, called biochar when used as a soil amendment, can be derived from nearly any biomass, transforming waste products into this unique additive. Increased bio-fuel production and increased fruit and nut crops in California produce a growing supply of waste that has rich potential as a nutrient. Wood, chicken manure, the residue of corn plants after harvest, and nut shells are all common candidates for biochar, each cooked down in a low- or no-oxygen environment into brittle charcoal and added to soil. 
The claims of biochar’s ability to improve soil are vast. Biochar proponents say its addition to soil can increase carbon storage, increase the nutrient and water retention of soils, and reduce the greenhouse gas emissions from soils.
“The basic premise of biochar’s benefit is straightforward,” says Sanjai Parikh, assistant professor of soil chemistry in the Department of Land, Air and Water Resources at UC Davis. “You are putting highly condensed carbon in the soil, so that biochar itself has a longer residence time that just putting a piece of wood, or any raw biomass, in the soil. The fact that biochar is a fairly recalcitrant form of carbon means that microbes cannot utilize it easily as food source and carbon dioxide emissions are thus temporarily reduced. However there is also a lot of excitement around the potential of biochar to also provide a host of specific agronomic benefits.”
But as a relatively young avenue of scientific research, conclusive evidence of its benefits is largely inadequate. To drive forward the understanding of biochar, Parikh, along with postdoctoral scholar Fungai Mukome have created the UC Davis Biochar Database — a forum dedicated to comparing the physical and chemical properties of biochar based on the various sources used to make them, and through that generate a broader understanding of the replicable benefits biochar can bring to soil.
“With our database we’re hoping to provide some of the basic data to the biochar community to link these benefits with specific biochar feedstocks and processing temperatures,” Parikh said.
The database, funded in part by the Agricultural Sustainability Institute at UC Davis, can be used as a resource for biochar researchers, manufacturers and users to better understand the effect that different biochars have shown in soil. Users can begin to tailor their biochar systems to better reflect the advantageous results that have been shown in biochar research. And for those studying the benefits of biochar, the database serves as an open source community that biochar researchers can add to in order to develop a comprehensive guide to the research.
“We released the database with 80 entries, and currently have over 300, but our goal is to grow the database to include 1,000 entries within a year,” Parikh said. “There needs to be a place to come to understand the properties of biochar, and opening the forum for community contributions is an important way to expand our knowledge.”
The biochar database can be visited at biochar.ucdavis.edu and contains instructions on how to download data, and how to contribute to the database by uploading data on biochar chemical and physical properties.
