Bio-acidification of livestock slurry with soja - melasse

Summary

Ammonia emissions from livestock manure represent a significant source of nitrogen pollution with impacts on people, animals, and the environment. Acidification of liquid manure (slurry) with sulfuric acid is a known method for reducing ammonia emissions, but sulfuric acid has a number of disadvantages which have limited the adoption of this technology. Bio-acidification offers an alternative method of acidifying slurry; in this system carbohydrates are added to manure under anaerobic conditions, stimulating production of organic acids which lower the pH. However, the exact effects of bio-acidification on pH and ammonia volatilization are still poorly understood, and effects on soil nutrient availability and plant growth have yet to be tested.
We examined the effects of bio-acidification of pig and cow slurries in four experiments, using a readily available waste product (sojamelasse) mixed with slurry at 10, 15, and 25% concentrations (by fresh weight). Our results showed that bio-acidification reduced slurry pH according to the amount added, with 25% concentrations (approximately 3% sugar in total mixture) sufficient to reduce the pH below 5. These effects lasted through several weeks of storage at 7 °C. In a second experiment, we found that bio-acidification reduced or completely inhibited ammonia volatilization, also depending on the amount added, though in the cow slurries these results were only temporary and final volatilization was greater than the untreated slurry.
In a third experiment, we found that N availability in soil over 5 weeks was mostly not affected by bio-acidification, other than a difference in ammonium content from the original materials. P availability was reduced, but the same effects were seen in sulfuric acid treatments, indicating that the effect was due to acidification in general, not bio-acidification specifically. Soil pH was higher after 5 weeks with bio-acidified treatments than with untreated slurry, representing an advantage of bio-acidification over sulfuric acid treatment. In a final experiment we measured maize growth over 5 weeks in a greenhouse, in soil amended with bio-acidified, sulfuric acid treated or untreated slurry. We found no positive or negative effects of bio-acidification on plant height or biomass.
Our results suggest that bio-acidification may be a viable option for slurry acidification, with several advantages over acidification with sulfuric acid. However, further study is needed to test effects at field scale and identify best management practices for bio-acidification on the farm.