Ever since humans began tilling soil, they have been using manure to restore its health. Modern research has proven that manure is a good source of nitrogen, phosphorus, and other essential nutrients and can also offer organic matter to improve soil tilth. Research at Cornell University now also shows a link between manure and crop yield.
While manure’s nutrient qualities can offset the need for commercial fertilizer, different types of manure with the same level of nutrients may not provide the same results. The researchers at Cornell are trying to identify the link between soil microbial biomass, yield, and nitrogen needs.
“We know there are essential nutrients in manure, which is well-established information,” says Dr. Quirine Ketterings, who leads the Cornell Nutrient Management Spear Program. “We are finding that fields that have had manure applied for multiple years have benefits over fields with less or no manure history. Some fields show a yield bump when manure is applied, others don’t. Some fields need extra nitrogen, others don’t. We are curious what is causing the yield bumps and whether microbes working in the soil can be used to identify when extra nitrogen is needed.”
Much of the Cornell team’s work has centered on corn production with the help of grower partnerships throughout New York state. The invitation to join the research stated the nitrogen fertilizer replacement value would be evaluated and the resulting yield differences occurring as a result of the manure application would be determined. Field trials were implemented using a design where there are six crop strips with three receiving manure and three without manure prior to planting of the corn. At side dress time, when the corn is about six to 12 inches tall, the strips are divided into sections that are side dressed with nitrogen fertilizer at different rates. This method identifies the most economic rate of nitrogen fertilizer for plants that received the manure and for plants that did not get manure earlier that season.
According to PhD candidate Gurpreet Kaur, for each farm trial, the team tests the soil before planting, confirms the level of nutrients in the manure, and then calculates the amount of fertilizer that is expected to be needed for optimal corn production at the test field.
“We collect soil samples at planting, before side dressing, and at harvest,” explains Kaur. “We test for many qualities – soil pH, organic matter, soil nutrients, and so on – and we determine microbial biomass at each of these time steps.”
The team takes soil samples at different depths as well. The four-inch depth is analyzed for total carbon and soil respiration. Collected sub-samples were frozen and will be processed for DNA sequencing. Samples taken at a depth of zero to eight inches are analyzed for soil fertility parameters similar to what a farmer would do to determine soil fertility status in a field.
Ultimately, the team hopes to identify the link between microbes, their composition and their activities in the soil, and corn management in terms of manure and fertilizer allocation.
“We want to understand what is causing the yield bumps,” says Ketterings. “We also want to know if we can use soil microbial indicators such as microbial biomass and soil respiration to determine where best to allocate manure and fertilizer resources.”
It is possible, according to the researchers, that understanding how the microbiology works could make applying manure to improve crop production a more exacting science. Currently, they don’t understand what drives the yield increase in some cases and not in others.
“Manure is a tremendous resource that already exists on most farms and this work is aimed at trying to understand how to best harness its value,” says Ketterings.
Results from the first trials conducted in 2022 and analyzed in 2023 showed “a range of possible responses” to the combination of manure and nitrogen fertilizer applied under the parameters of the study. One trial did not show a yield increase or any nitrogen benefit from the manure application. Another test area showed a yield increase when manure was applied that could not be attributed to the addition of nitrogen. A third plot had both a yield and nitrogen benefit from the inclusion of manure in the crop. Besides indicating that more research is needed to understand these varied results, the team expects to determine by the end of the study where manure application can be targeted to provide the greatest gain.
The research program continued to focus on corn production following the same protocols through the 2024 crop year. The team expects to have answers, and possibly some concrete recommendations, by the end of 2026. But different types of manure could have different microbial properties and might react differently in other crops, so additional work might be needed.
“Many farmers already recognize the benefits of manure application,” says Ketterings. “Our main goal is to develop guidance for manure use that will benefit dairy producers who already manage manure, but also those who grow crops but don’t have animals on the farm.”
The research is creating a picture for growers to see what is happening below the surface of the field. If they can understand what is happening in the soil, they might be able to adjust their crop management to benefit from and enhance what is living beneath the surface. Asked if the team believes that, in the future, microbial additives could be created to boost the effectiveness of the manure, they agree that anything is possible. But, for now, they just want to understand how the system works because even that will give producers useful information to aid in crop production.
The research has attracted the attention and support of a diverse group of stakeholders. The Towards Sustainability Foundation, which sponsored the soil sampling in 2023, sees the potential results as adding to the preservation of the environment by helping farmers manage manure and soil health. The New York Farm Viability Institute, Northern New York Agricultural Development program, and various state agriculture and conservation departments view the research as beneficial to their many stakeholders as well.
Ketterings agrees that this examination of manure, and how microbes within it contribute to improve crop development, could possibly guide manure and fertilizer management decisions. The understanding of the interactions between soil, manure, and fertilizer rates and application may be an important aspect of sustaining agricultural production.
According to Ketterings: “Our goal is to determine which fields will benefit from manure and how much nitrogen could be saved with the ultimate objective of achieving better yields with a lower environmental footprint.”
For some farmers, who apply manure knowing it offers nutrition but who also think spreading it on a field is a way to deal with waste, learning how it can increase yield could change their farming practices. Understanding microbial action in the soil and how it could signal whether additional nitrogen is needed may help growers use manure more judiciously. •
