Manure advocates have long agreed that animal manure is anything but waste, especially when it comes to improvements in yields. However, increasingly, studies are looking at manure’s effects on soil health – which also pays off in terms of improved yields in the following crop year.
Win-win, right?
Recent research from Prince Edward Island looks at the impact of manure combined with residue from cover crops on soil health, specifically when it comes to one of P.E.I.’s most important exports: potatoes.
Manure is not as commonly used in potato production systems as it is for other crops, although cover crops are gaining popularity on the island. “Potatoes are grown in light, sandy soils,” says Dr. Judith Nyiraneza of Agriculture and Agri-Food Canada (AAFC). “They are known to be succeptible to be eroded.” Additionally, she says, because potatoes leave such minimal crop residue, the carbon input is low. As such, farmers often look for ways to increase soil organic matter while also increasing yields.
Combining manure with cover crops is not a new practice – it’s been around for decades, and in fact, we’ve covered advances on the combination in a 2024 issue of Manure Manager. However, the two are still viewed by some as an either/or – cover crops that are incorporated into the soil are often called “green manure,” implying that they are an alternative. However, the P.E.I. study, along with recent and ongoing research in the U.S., suggests cover crops and manure, which are both imperfect solutions alone, could do amazing things together. “We know manure is a stable carbon,” she says. “But manure is not a very accessible source in P.E.I.”
The study
The two-year P.E.I. study was executed by Nyiraneza. It investigated the use of dairy manure mixed with straw and high-residue cover crops in potato production systems. Working off of recommendations from Living Lab Atlantic partners including the P.E.I. Potato Board, Nyiraneza planted numerous field plots and treatments at the Harrington Research Farm, reflecting the fields of P.E.I. farmers.
The team looked to stydy eight different cover crops (three annuals and the others perrennials that were mowed off) with manure applied. Tillage was also reduced on the perennial plots, but annuals had more tillage and less mowing. The crops were planted in the spring at least one year prior to potato planting season, with pen-pack manure applied during the cover cropping stage. The crops were studied to see how the manure affected yield, soil health, soil diseases and nitrate leaching. In general, incorporating manure into cover crops increased total potato yield by 28 percent.
The big winner crops were pearl millet and sorghum sudangrass for increasing yield and reducing levels of root-lesion nematodes. Pearl millet is relatively new to P.E.I., but is considered a “super grain” for its climate resilience and ability to withstand short growing seasons and high stress.
Nyiraneza says although dairy manure might not be as readily available to P.E.I. growers, those with access are encouraged to incorporate it into their fields. In general, producers are encouraged to adopt mixed farming by integrating livestock production into horticulture fields. •
