Research Update: Evaluating Different Types of Swine Manure for Hybrid Rye Production

By Melissa Wilson and Yuzhi Li

Key Points:

• As one part of a larger study, we’re growing hybrid rye using swine manure as the primary nutrient source
• In the first year of the study, the use of liquid swine manure tended to produce higher grain yields than solid or composted swine manure
• Application rates that supplied 60 to 120 pounds per acre of first year available nitrogen optimized yield without significantly overapplying phosphorus and potassium
• Hybrid rye grain and straw produced for the larger study will be tested as an alternative feed and bedding source for organic swine production

What we did:

Hybrid rye is being grown in Minnesota as an alternative to traditional winter rye varieties. In organic production systems, the grain may be used as an alternative feed for livestock while the straw can be used for bedding. A new research project is evaluating hybrid rye for swine production, so we wanted to know if various types of swine manure (liquid, solid, or composted) could be used as a primary nutrient source.

In fall 2021, we started a field trial at the West Central Research and Outreach Center (WCROC) in Morris, MN. We applied five different rates of each type of manure in early September to supply zero to 240 pounds of first-year available nitrogen per acre. We assumed 75% of the total nitrogen would be available the first year for the liquid and solid swine manure and 40% would be available from the composted swine manure. After application, we incorporated the manure within 12 hours and planted hybrid rye within the next few days. The following summer, we harvested the rye and analyzed the grain for crude protein.

What did we find?

The first of this two-year study has been completed. We found that use of liquid swine manure resulted in the highest grain yield (around 100 bushels per acre) compared with solid and composted swine manure, which produced around 80 bushels per acre each at the highest application rates. Interestingly, the crude protein was not affected by nutrient source, suggesting that nitrogen may not have been the primary reason for the decreased yield with the solid and composted swine manure. In general, crude protein increased with increasing application rate, regardless of the nutrient source.

Hybrid rye yield was not significantly increased when liquid swine manure was applied above 120 pounds of first-year available N per acre (about 5,000 gallons per acre). This is in line with fertilizer recommendations for conventionally managed hybrid rye (110-150 pounds of N per acre depending on previous crop). For solid and composted manure, yield was not significantly increased above 60 pounds of first year available nitrogen per acre (about 4-5 tons per acre). Higher rates improved yield slightly, but significantly overapplied phosphorus and potassium (anywhere from 60 to 400 pounds of phosphorus and 115 to 480 pounds of potassium!). When working with manure, there is always a balance between optimizing the use of nitrogen while preventing buildup of soil phosphorus to very high levels.

What’s next?

Hybrid rye was also grown on a larger field at the WCROC to supply feed and straw bedding for the organic swine herd being raised in hoop barns. Swine scientists Yuzhi Li and Lee Johnston will be replacing 50% of corn in the swine diet with hybrid rye grain and comparing it with a typical corn soybean meal-based diet. They’ll monitor the growth and health of pigs as well as meat quality. Researcher Joel Tallaksen and Professor Bill Lazarus will be evaluating the economics and impacts of the entire system. Their goal is to see if integrating winter hybrid rye into pig production is viable for organic farmers and whether it can improve environmental outcomes by increasing crop diversity compared with a typical crop rotation.

This experiment is fairly unique in that it’s evaluating the full cycle - from hybrid rye, to feed and bedding, to animals, to manure, and back to hybrid rye. We’ll be repeating the full experiment again in the upcoming year. As far as the field trials, manure was applied again this past fall in a new field and hybrid rye was planted. We’re now waiting to get through the winter to evaluate if there was any stand loss!