Manure – Waste or Resource?

Manny Sabbagh

University of Minnesota


  • Soil Health

Many people view manure as just a pile of waste, yet this combination of feces, urine and bedding material is so much more than that. An inevitable byproduct of the livestock industry, manure can be an inexpensive tool to improve the soil and the plants we grow for food, fiber and fuel. With some supplementation from synthetic sources, manure can supply plants with the macro- and micro-nutrients needed for proper growth and production. My research as a FFAR Fellows Program at the University of Minnesota focuses on identifying optimal manure management strategies, with a specific focus on the use of cover crops, to help growers while also protecting the environment.

Timing of application is key to making optimal use of manure. The intent is to keep the nutrients from the manure in the soil to be used by the plants while minimizing loss, particularly nitrogen and phosphorus. While timing and temperature factors point to late spring and early summer as ideal times to apply manure for a summer crop, the typically wet spring soils make waiting until then to apply manure a huge gamble for farmers. It is nearly impossible to apply manure when soils are overly wet since the heavy machinery used to apply manure can easily get stuck and compact the soil. For this reason, farmers often apply manure in the late fall. Unfortunately, this means there is ample time between manure application and spring planting during which nitrates, an environmentally harmful form of nitrogen, have a higher risk of being offloaded into waterways, rather than being taken up by growing plants.

The offloading of nitrate from agricultural fields, specifically from the upper Midwest into the Mississippi River, is one of the main causes of harmful algal blooms in the Gulf of Mexico.

Algal blooms in the Gulf of Mexico largely attributed to nitrate offloading from agricultural lands. Source:
National Oceanic and Atmospheric Administration.

My research examines the use of cover cropping to address nitrate leaching and other environmental concerns from fall manure application. Cover crops are typically not planted as a commodity crop but are used in agriculture for their numerous environmental services, such as soil stabilization. A cover crop planted in the fall takes up nutrients out of the soil, effectively acting as a savings account for nitrogen and other nutrients as well. Once the cover crops are terminated, all the nutrients stored in their biomass are released as they decompose, acting as a green fertilizer for succeeding crops such as corn, cotton or soybean. Although cover crops are increasingly used in agriculture, in the upper Midwest cover crop adoption is still low compared to other regions. This is due to the exceedingly cold late fall and winter seasons that do not allow for much cover crop growth; farmers are not too keen on expending resources to plant a cover crop that may not survive winter temperatures.

To enhance cover crop adoption and potentially limit nutrient losses, we are collaborating with the Minnesota Corn Research and Promotion Council (MCR&PC) to conduct small plot studies at the University of Minnesota Research and Education Center in Waseca, MN. We are interseeding cover crops into maturing cash crops (prior to their harvest)to expand the cover crop growing season and to potentially have an active root system established after cash crop harvest and prior to manure application. Having an active root system present prior to manure application in the fall may help take up readily available nutrients supplied by manure.

Applying liquid injected swine manure into a stand of growing cover crops.

We are collecting and analyzing soil and plant samples throughout the early spring until the late fall, prior to soil freezing. Data collected from this study will be used to measure changes in soil health, nutrient cycling and agronomic responses. The goal of this study is to develop best management practices for integrating cover crops with liquid injected manure. In the short-term, we hope to see greater interest in cover cropping among upper Midwest farmers which can lead to long-term improvements in soil health.

Collecting cover crop biomass samples in the late fall to measure growth and nitrogen uptake.

I am beyond excited to work with my Rockey FFAR Fellows sponsor, MCR&PC. It is a great feeling that the checkoff dollars that farmers provide are actively being used to research and develop novel approaches to sustain and improve corn yields while also helping the environment. Through the mentorship with Dr. Maciej Kazula, director of research, I am gaining great experience in networking and especially communicating research findings to a diverse audience. Dr. Kazula is always actively seeking ways for me to showcase my research and is a great support and resource. With graduation still a few years off, I feel quite privileged to be able to utilize my Rockey FFAR Fellowship and learn many soft skills that will put me at a great advantage once I enter the job market.

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