Advancing 4R Nutrient Stewardship for Sustainable Use of Phosphorus from Pig Manure Slurry for Crop Production

Project 20-003 - Dr. Paul Voroney, University of Guelph

Pig manure slurry (liquid) is a source of valuable crop nutrients that enhances soil fertility and a source of organic matter (OM) that improves all soil properties (i.e. both soil quality and soil health). Ontario is among the most intensive hog manure producing areas in Canada with 5.5 million hogs marketed in 2018. These hogs produced >6 million tonnes of manure containing ~250,000 tonnes of N and 72,000 tonnes of P.

Studies have shown that the presence of OM in animal manures and composts delays formation of stable forms of P in soils which are otherwise unavailable to crops (1,2,3,4). This may explain why P in pig manure slurry appears to be similar in plant availability to commercial fertilizer P, despite having a lower soluble P content. If OM favors the formation of labile P forms over stable P forms in calcareous and acidic soils, soil P fixation can be decreased, P-use efficiency increased, and therefore excess P fertilization could be avoided.

While the benefits of OM in pig slurry to soil are well known, its role in governing soil P chemistry is not well understood. Dr. Voroney’s research will clarify the effects of pig slurry OM on the chemistry of soil and fertilizer P and validate Ontario’s current soil P test in soils amended with pig manure slurry. When improperly managed as a nutrient source for crop production, pig manure slurry can be a serious environmental concern, especially when application rates are based on N supply alone.