For the layperson, a product composed of pig excrement, urine, and leftover feed and water might be hard to embrace. For farmers and scientists, however, slurry holds much promise in addressing emissions. 

“Slurry has long been recognized as a great fertilizer with a proven ability to maintain production levels on farm. Unfortunately, too much application in regions of dense animal production has given slurry some bad press,” says Dr. Marie-Pierre Létourneau Montminy, Canada Research Chair in sustainable animal protein production and assistant professor at Université Laval. 

Using four feeding regimens with various ratios of phosphorus (P) and nitrogen (N), the study is generating four types of pig manure and applying them to crops as fertilizer. 

“A pig trial was performed - using twelve environmentally controlled stalls housing four pigs per dietary treatment - to test the interaction between N and P. Over four weeks, the treatments were evaluated for growth performance, water intake, body composition, gas emissions, and slurry volume, including its concentration in N and P, and its pH." 

N and P have an environmental impact when applied in excess, while high pH increases ammonia losses 

As a result of these trials, four slurry types have been produced and sent to the University of Manitoba, where soil scientists are evaluating them for leaching and runoff potential, as well as GHG emissions. 

At Université Laval, Dr. Lotfi Khiari is gauging the fertilizer potential of the samples compared to chemical products and determining which slurry would be most effective in that regard.  

Work is also ongoing with Agriculture & Agri-food Canada at the Sherbrooke Research and Development Centre to assess the slurry samples for biogas production. Biogas is a renewable energy source produced from raw materials such as agricultural waste and manure. 

“Thus far, we have confirmed that we can alter N to P ratios without impacting growth performance. Using a simulation model, we predicted the retention and excretion of N and P by pigs and compared that to what occurred on farm.” 

This is notable for producers, as it means that science can design diets and accurately predict the N to P ratio in the resulting slurry.   

Starting in February of 2026, a second phase of the study begins, focused on fiber and protein digesting enzymes in swine diets.  

“In general, the more fiber is digested by an animal, the less it can be emitted as methane. Protease [a type of enzyme needed to digest protein] is also of interest. It is produced naturally by the body but can also be supplemented in animal feed. If we can further degrade proteins, we may be able to reduce emissions. Combine that with better digestion of fiber, and there should be a marked benefit to the environment.” 

Though manure science may lack glamour, it places green ag squarely in the spotlight. 

“When you consider the environmental impact of swine production, it is due largely to manure and manure’s use as fertilizer. For that reason, we have made manure a priority in our project. While we have already developed some strategies to lower emissions with feed, crop production is also a factor, as chemical fertilizers affect both feed and manure. By producing manures with a better balance of N and P, we could reduce the need for chemical fertilizers going forward.” 

To further aid the planet, this study is also crafting strategies to lower methane emissions during the storage of slurry. 

In the months ahead, work will continue on two fronts, which include modelling in the lab and applying strategies on farm under real world conditions. The latter includes testing various methods of using manure for biogas production to find the most efficient option.  

The end goal of this project mirrors the linchpin of SIP’s agenda: Finding practical solutions that address industry issues and aid the bottom line. 

“We want to identify the best strategies for producers, but if those approaches are too costly, no one will implement them, so we really need producer input and involvement along the way.” 

Apart from supporting a greener planet, this study positions pork production as efficient, conscientious, and committed to a brighter future. Plus, if there is a carbon tax to contend with, or a premium paid for sustainability, the results could save producers money or strengthen competitiveness by reducing their environmental footprint. What’s not to love? 

“Swine manure is an excellent source of nutrients that are essential to crop production, while also offering cost savings compared to synthetic fertilizers” says Dr. Tiequan Zhang, senior research scientist with Agriculture & Agri-Food Canada (AAFC). “Nitrogen (N) is one of the multiple essential nutrients contained in manure, in both mineral and organic forms.” 

In mineral form, N is readily available to crops in the year it is used. The organic form of N needs to be broken down into mineral N before being applied to crops, and one year of manure application can provide crops with N for multiple growing seasons. In order to maximize crop yield in an environmentally sustainable manner, however, scientists must determine the legacy value of the N, a key focus of this study.  Legacy values in fertilization refer to the long-term effects of fertilization practices on soil nutrient availability. 

“To determine those values, we conducted greenhouse studies using soils from fields that have been treated with liquid and solid swine manures over 19 years. We then compared the results with soils receiving synthetic fertilizers over the same time frame.” 

Using a corn-soybean rotation, broadcast application of manure or synthetic fertilizer was made  to the corn phase of the rotation, with residual nutrients picked up by the soybeans.  

“In this case, we found that long-term pig manure applications generated significant residual N impacts on crop growth over a growing season. As a result, added fertilizer nitrogen rates could be markedly reduced at the same yield level, leading to substantial savings in fertilizer costs. However, it is worth noting that the results are preliminary and obtained under greenhouse conditions, so they need to be validated and calibrated in the field.” 

Relative to synthetic fertilizer, soils receiving pig manure showed higher soil organic carbon, improved soil aggregate stability and better soil health. Together, these enhancements produced a 19% increase in crop yield potential. 

“We were encouraged to see that N losses were less in soils with swine manure than those with synthetic  fertilizer. The N loss reduction with swine manures were 56-78% over the non-growing season. Those soil nitrogen losses would have happened to the air through denitrification or to the water through leaching.” 

Denitrification is a microbial process that converts nitrate into nitrogen gases. This process removes bioavailable nitrogen and returns it to the atmosphere. Nitrate leaching occurs when excess water carries nitrates through soil into groundwater, posing potential health risks to humans. 

By replacing chemical fertilizer with swine manure, the industry could produce significant environmental benefits through reduced greenhouse gas emissions and improved water quality.  

As producers strive for financial sustainability in a highly competitive business, this project is a prime example of knowledge unlocking efficiencies. In an industry where costs continue to rise, fertilizer is a major expense in crop production, so alternatives like swine manure that promise savings are worth their weight in gold. 

“In seeking to enhance producer profits from crop production, a key aspect is maximizing the benefits of both swine manure and chemical fertilizers. Through 4R recommendations, we can optimize the use of swine manure and chemical fertilizer and better match nitrogen and phosphorus levels to crop needs.” 

The 4R Nutrient Stewardship framework is designed to enhance nutrient management in agriculture while considering economic, environmental, and social factors. The four principles are right source, right rate, right time and right place. 

Those recommendations play a critical role for the environment as well. By avoiding over-fertilization and lowering nutrient loss to the air and water, growers can reduce environmental harm and make their operations even greener. 

As this study demonstrates, the benefits of swine manure as an alternative to synthetic fertilizers are many and varied. Of course, for change to occur, producers and industry must be aware of manure’s potential, so researchers are seeking to spread the word. In the process, they hope more growers will consider foregoing synthetic fertilizer in favor of more efficient, affordable and eco-friendly manure.  

“Moving forward with this project, we are continuing to identify the maximum economic fertilizer rate in soils that previously received swine manures, as well as the true fertilizer values of swine manure nitrogen in the season of application and over the long-term.”