Manure contains essential nutrients for forage crop growth. How and when it is applied will impact its use by alfalfa, grass and corn silage crops.
At a virtual symposium hosted by the Midwest Forage Association, Wisconsin Custom Operators and Professional Nutrient Applicators Association of Wisconsin earlier this year, Quirine Ketterings shared the basics of manure nutrients and the results from five projects conducted in New York to see how to get the most value out of manure. Ketterings leads the Cornell Nutrient Management Spear Program (NMSP), which aids in the development and implementation of agronomic and environmentally sound nutrient management practices at dairy and other livestock farms and cash grain operations.
“We want to recognize manure as a source of nutrients that contains all of the essential nutrients for crop growth,” Ketterings said. In terms of major macronutrients, the availability of phosphorus and potassium in manure is considered close to that of commercial fertilizer, but nitrogen is different. “That’s important to understand because it sets the stage for how we could improve the value of manure for nitrogen,” she said.
Nitrogen is recognized in two fractions – inorganic and organic. The inorganic fraction is similar to urea fertilizer, especially if it can be incorporated into the soil or applied during the growing season. “The longer we wait for the incorporation of that manure, and if the manure is surfaced applied, our system assumes that most of that inorganic nitrogen will be lost before the plants can make use of it,” Ketterings said.
The organic fraction acts similarly to a slow-release fertilizer that needs to convert to nitrate over time. This fraction is credited over a three-year time period. Most is credited in the year of application with some carryover to years two and three. “Herein lies the opportunities to increase the value of the manure,” she said. “The quicker we can incorporate manure, the better our chances; and the closer we get to the time that the crop actually needs that nitrogen, the better we can benefit from that manure.”
Ketterings summarized five projects to find more ways to optimize the value of manure:
1. Injection of manure in alfalfa/grass fields
A consultant and custom manure hauler came to NMSP asking if manure could be injected into established hay fields or if it would damage the stands and result in a net negative impact. The project was designed with four treatment types:
- No manure and no injection equipment to serve as a control
- Injection equipment passing through without manure to determine mechanical impact
- Injection of liquid dairy manure into the hay stand
- Surface-applied manure with no injection
The trial occurred at two locations. The Aurora research farm had old stands – one in alfalfa and the other in tall fescue. There were 4,000 gallons of manure applied after the first cutting in the first year and 8,000 gallons applied after the first cutting in the second year. The Harford location had higher-yielding fields. Manure was applied at 4,000 gallons after the fourth cutting in the first year and 8,000 gallons after the first cutting in the second year.
At Aurora, fields with manure application had drastically increased yields compared to plots that did not receive manure. The Harford location with the higher-yielding stands did not see a yield increase from the addition of manure. In terms of mechanical damage from the injection equipment, there was no difference across all locations. “These results would suggest injection can be implemented without negatively impacting yields in the hay crops,” Ketterings said.
2. Chisel versus shallow mixing for corn
To answer the question, “Can we still conserve the nitrogen if we do shallow incorporation instead of more aggressive tillage?”, this study compared chisel plowing with aerator mixing. Liquid dairy manure was applied, and the aerator followed directly behind under a 15-degree angle. They looked at corn silage yield, crude protein for quality, and milk estimates in pounds per acre.
The average yields across seven locations increased by one ton per acre when manure was incorporated, compared to only surface applied, with no difference between the chisel plow and aerator. Milk estimates were up more than 1,000 pounds per acre for tillage versus no tillage, and no difference in tillage method.
Ketterings noted there were a number of sites where there was no yield increase. At those locations, the crude protein levels were consistently higher. “For those locations, nitrogen wasn’t an issue to start with,” she explained. “There was plenty of nitrogen to go around. ...We didn’t need to incorporate to capture extra nitrogen.” From this work, she concluded that shallow incorporation is suitable for incorporating manure.
3. Direct seeding of corn after manure injection
Working with a dairy farm in western New York, field trials were set up to look at tillage depth – 0, 7 and 14 inches – as zone building for two years, followed by tillage intensity for three years. “We looked at things like density, nitrogen availability, silage yields and quality, and basically concluded that the tillage depth for this particular farm didn’t matter,” she said. “The farm could stop with the zone building exercises and still get the same silage yields, not impacting anything else.”
Tillage intensity compared reduced tillage with an aerator plus zone tillage to reduced tillage without the zone tillage, as well as no-till where corn was directly planted after manure injection into the field. There was no difference in yield, quality or nitrogen credits across the treatments.
Ketterings said they concluded that “When farms have made significant efforts to adopt soil health practices, manure injection followed by no-till planting without seedbed preparation or zone building can sustain yields and conserve nitrogen while reducing soil disturbance, risk of phosphorus runoff and tillage-associated fuel, equipment and labor costs.”
4. Sidedressing of standing corn
By sidedressing manure in the summer, the idea is to apply nutrients closer to plant uptake and avoid having to apply manure under extremely wet conditions at other times of the year. Working with a dairy farmer in central New York, prototype equipment allowed for surface application of manure between rows of standing corn.
From the first study, they learned that one application within the season is sufficient. The next two years, they focused on nitrogen rate. Three strips of the field received a sidedress surface application of manure mid-season. The other three strips did not have the manure pass. Nitrogen fertilizer was applied over the top at varying rates. Where manure was sidedressed, the added nitrogen fertilizer did not increase the yield.
In addition, the manure application increased yields beyond what could be achieved with nitrogen fertilizer alone. “Basically, it shows the benefits of manure, both in terms of nutrients and in terms of increasing actual yield,” Ketterings said. She concluded that side dressing manure mid-season helps avoid application times when soils are wet and nitrogen loss can be high. It can also eliminate the need for nitrogen fertilizer.
5. Carryover of yield benefits from corn to alfalfa
Exploring the idea that manure benefits go beyond nutrients in the current year of application, a study looked at five years of corn silage followed by five years of alfalfa. Manure was applied during the corn years as compost, liquid manure, no fertilizer and nitrogen fertilizer at 100 pounds per acre (the optimum rate for that location). No manure or fertilizer was applied during the alfalfa years.
Alfalfa yields were low in the establishment year and again the following year due to a record drought, but they were higher the next three years, and the impact of the compost and manure applications could be seen. Those treatments consistently outyielded the areas where no fertilizer or only nitrogen fertilizer was applied in previous years. “Manure compost applications had significant impacts on crop yields even years after the last application,” she said.
From these five projects, it can be seen that conserving nutrients and applying manure when it’s most useful for the growing crop can not only increase yields and replace the need for additional fertilizer, but also benefit future crops. Ultimately, it maximizes the value of manure.
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