The misconception about manure being just a waste and harmful biproduct of the cattle and livestock industry is still a big concern. A group of researchers and extension educators have joined efforts with farmers across Nebraska to find the value of manure as a source of nutrients in crop fields in the Sandhills and reduce the environmental impacts caused by this industry. At the same time, they are trying to incorporate residues from red cedar trees that are currently threatening the Nebraskan wildlife and ecosystems due to its rapid expansion. 

Animal feeding operations in Nebraska generate significant amounts of manure that can provide essential plant nutrients, organic matter, and active microbes to cropland. Additionally, Eastern red cedar tree (Juniperus virginiana) encroachment in grazing land has become an economic and ecological threat. Some farmers believe that, together, manure and woody biomass (created from tree management activities) could benefit soil quality.

Finding manure and woodchips benefits to the soils of Nebraska

Their interest in testing this idea helped launch a three-year study to test the impacts of these treatments in small field plots at two farms in the Sandhills. Results of those studies showed that woody biomass combined with manure amendments have a positive impact on soil physical properties, as it increases sorptivitiy, improves soil organic matter and decreases bulk density More information regarding the benefits of manure on crop fields can be found here.  In late 2018, this project was expanded to include on-farm research using large plots (approximately 40’ wide and 350’ long) at four locations across the state of Nebraska – near Saint Paul, Pierce, Ainsworth and Brule. Two more study sites have been added this year – near Julian and Overton.

The primary goal is to evaluate potential short- and long-term impacts on soil quality and crop productivity of utilizing manure and red cedar woodchips as soil amendments on cropland that has not received manure for several years. Plots were established at the initial four sites prior to the 2019 growing seasons to accommodate at least three different treatments (manure, manure+woody biomass, and control plots that received only inorganic fertilizer) with each treatment replicated four times. Manure sources for these sites included beef feedlot manure at two sites and bedded beef barn manure or beef slurry manure at the other two sites. At the site near Brule, woody biomass was replaced by coal char from a Colorado sugar beet processing plant since wood chips were not readily available. Preplant nitrogen was the same among all plots within a single site, whether supplied by manure, fertilizer, or a combination of both.

Soil samples were collected before treatment applications at all research sites to determine initial soil chemical, physical and biological properties. Subsequent samples were collected at the end of the 2019 cropping season and corn yield was determined for all research sites.

Soil and crop improvements after the first year of treatments

Results from the sites studied during 2019 indicate that applications of beef manure make significant contributions of nitrogen (N), phosphorus (P) and potassium (K) in crop fields without compromising yield, indicating that manure is a reliable source to replace preplant nitrogen normally delivered in inorganic fertilizers. There is no evidence that woody biomass contributed to soil acidification or nitrogen immobilization with surface application. Further applications over additional growing seasons are expected to generate measurable changes in soil physical and chemical properties. Sugar beet coal char application produced an increase in soil organic matter, pH, and sulfate sulfur in the top two inches of the soil; however, a 16% yield decrease was observed following a single coal char application. Other studies have demonstrated yield benefits following cropland application of biochar or similar materials, so additional research is warranted before making definitive conclusions about the use of coal char as a soil amendment. Crop yields were not negatively impacted by any of the remaining treatments.

A second year of applications for all treatments except coal char (at the four original research sites) is expected to reveal further changes in soil composition and nutrient availability following the 2020 crop season. Residual impacts of a single application of coal char will be studied at the site near Brule. The sites near Julian and Overton that were added prior to the 2020 growing season were laid out like the other sites and received swine slurry and beef feedlot manure, respectively, along with woody biomass, manure+woody biomass, and inorganic fertilizer as a control. Additional data collection to assess the potential of woody biomass to retain moisture will be evaluated in the plots near Julian where no irrigation is applied to the crops. Moisture sensors will be installed in each plot and data will be compared among treatments.

While it can take multiple years before changes in some soil properties can be measured,  the immediate impacts from a single manure application include addition of organic matter and microbes that support the soil biological community, increased pH and increased electrical conductivity. Likewise, the use of manure to meet pre-plant crop nitrogen needs can have immediate positive impacts on crop growth. The guidelines for manure nitrogen credits can be found at this link.