As is the case with most thorny conundrums, the dairy manure situation in Idaho also presents interesting opportunities. Only two other states surpass Idaho for milk production, and manure therefore abounds in the southern part of the state where most dairies are located. The conundrum: too much dairy manure to be used as fertilizer on crop farm acreage. The opportunity: create useful bioproducts from that manure.
In 2020, a project to investigate these bioproducts was launched by the USDA’s National Institute of Food and Agriculture. It has provided $10 million in funding to over 20 researchers at University of Idaho and wraps up in 2026. These researchers are building on decades of research in several areas, including better technologies to separate and process manure to use as feedstocks for soil amendments or additional applications, further investigation into manure biochar and production of biodegradable plastics from manure.
Before we dive into these exciting developments, however, let’s check in with U of Idaho economist Dr. Jason Winfree on the viability of bioproducts from manure. He first explains that it’s difficult for anyone to say which innovations have the best prospects.
“For example, manure pellets are easier to transport, but require a large amount of energy costs,” Winfree says. “Bioplastics seem to have potential, but consumer acceptance is an issue. There are many benefits from biochar. Biochar can help increase crop yields and consumers are willing to pay a little bit more if they understand that the production process was a bit more environmentally friendly. So, it’s an issue of both reducing the cost of creating the biochar and educating consumers about the process. In the end, since we are not sure which innovations will eventually become the most economically viable, I think there are benefits from working on various technologies.”
Bioplastic production
Scientists have known for decades that bacteria can convert carbon in feedstocks such as corn sugar into polymers (plastic) and store it – but as far as he knows, Dr. Erik Coats (the lead scientist on this project) is the first to do it with manure.
“There has been quite a bit of research over the last 20 years using pure bacterial cultures with refined feedstocks and there is already a market for the bioplastics produced,” he explains. “There are more challenges with using a mixed microbial community, which is what we have in with manure in our bioreactor, but we’re working through those challenges.” Coats is referring to his software model that takes data from sensors in the reactor (mainly dissolved oxygen readings), translates that into a system-level picture of plastic production and provides direction on when it’s time to add more manure/bacteria to keep plastic production at a high rate.
Regarding the resulting bioplastics mixture, Coats and his team have already published results on purifying it, but he also notes that there’s no need to purify it for many exciting applications. “We can heat the mixture and it can melt and crystalize with other biodegradable materials to produce a biodegradable composite,” he explains. “One option for this composite is to produce planter pots and trays for nurseries. We’re doing a lifecycle assessment now and ROI analysis, and if we can demonstrate an acceptable ROI, someone can commercialize this.” Coats and his colleagues have also developed a way to capture and concentrate phosphorous (P) from the bioreactor that can then be used in commercial fertilizer.
Better separation
In another project, centrifugation has been demonstrated as a successful secondary separation technique in recovering significantly more nutrients from dairy manure as opposed to using only an inclined screen. Dr. Lide Chen notes that more than 50 percent of the solids in liquid dairy manure are particles smaller than 0.5 mm and commonly used on-farm inclined screens typically have pore sizes larger than 0.5 mm. Most of the total P in liquid dairy manure is attached to fine particles smaller than 0.5 mm, he explains, “so to remove P from the liquid stream, advanced separation methods such as centrifuges are required.”
In on-farm tests, Chen and his team have shown that centrifuge-separated solids contained a year-long average of 8 Ib/ton of P (as P2O5) versus 2 Ib/ton from screen-separated solids. For total N, it’s 9.2 Ib/ton versus 5.4 Ib/ton, and for K (as K2O), it’s 7.2 Ib/ton versus 4.4 Ib/ton.
Chen and his colleagues have also investigated ammonia removal from dairy manure using thermal stripping with sulfuric acid absorption. In lab tests using anaerobically digested liquid manure, they achieved 93 percent removal of ammonium sulfate.
Compost
In this area, researchers have developed, built, tested and implemented a pilot composting system for benchmark-scale composting and air emissions monitoring. They have also completed the first run of dairy manure composting using amendments including clinoptilolite (zeolite), wood chips, biochar and pumice.
“We are excited that incorporating biochar, wood chips and other carbon-rich materials into composting manure results in a very-high value product that’s going to open large new markets for composted dairy manure,” says Dr. Mario de Haro-Marti, extension educator of Agricultural Environmental Management at U of Idaho Extension. “Owners of greenhouses and landscaping businesses have historically been rather shy of dairy compost because there hasn’t been solid data about the carbon and nitrogen content. They have also been concerned about salts, which are commonly found at a high level in dairy manure. Now, they will have the assurance from our data that they are getting a very high-quality composted product. It can be provided in bagged form or by the cubic yard by truckload.” He adds that there is a company in Boise that is already making and selling a value-added dairy manure very successfully. “There is more demand than production,” he says.
De Haro-Marti and his colleagues are also doing studies also with zeolites (minerals mined in Idaho) and getting very good results in terms of decreasing ammonia emissions and retaining nitrogen from fresh and composted dairy manure.
Mapping manure distribution
And although the bioproducts research is very exciting, this greater National Institute of Food and Agriculture project does not ignore the potential of using more manure on Idaho fields. In this area, Dr. Eric Brauns and his colleagues have been have analyzing the “optimal” spatial distribution of dairies to maximize manure nutrient uptake by crops and the “optimal” spatial distribution of cropland, given the current distribution of dairies and crops grown in Idaho. This will provide insight into the current supply chain of dairy manure and challenges in distributing dairy manure nutrients, as well as whether the capacity to utilize more manure nutrients in crop production has increased or decreased over time due to changes in dairy industry characteristics and cropping pattern changes.
Brauns and his colleagues have also been analyzing data related to manure application in terms of water quantity and nutrient cycling which includes soil moisture and rainfall. They have made substantial progress with the calibration and assessment of the nutrient cycling and leaching algorithm in their model. Evapotranspiration, soil moisture and crop uptake algorithms in a ‘SWAT’ model for irrigated conditions in the Magic Valley have been completed.
In this area of using more manure on fields, de Haro-Marti reports “we are also looking at how adding more dry manure to fields supports double-cropping, which is a great way for farmers to boost profits. We are investigating interseeding/double cropping with corn silage and cover crops, and also planting cover crops right after corn and tilling those in as green manure for the next crop. We are checking N leaching up to 4 feet deep, measuring corn yield and corn quality, and many other parameters.”
Looking forward
Dr. Mark McGuire, distinguished professor at U of Idaho and project director for the Idaho Sustainable Agriculture Initiative for Dairy (ISAID), is very pleased about all the progress with these projects.
“Scientists at the University of Idaho have identified several innovative processes to extract and utilize valuable nutrients from dairy manure,” says McGuire. “These technologies – ranging from making bioplastics and biochar to nutrient recovery systems and advanced composting – demonstrate that environmental stewardship and economic opportunity can go hand in hand.” He adds, “the collaborative work being done here not only benefits producers and rural communities but also provides scalable solutions for agricultural systems worldwide.” •
