Research Highlights

Research Highlights
Evaluating Poultry Litter Value for Nutrients and Soil Health

Harvesting soybean plots fertilized with poultry litter. Photo: South Carolina State University

By Laura Temple

Though synthetic fertilizers have increased crop yields, Bhupinder Farmaha, assistant professor and nutrient management specialist with Clemson University, notes that they have not maintained soil health. 

“As we learn more about soil health, we want to encourage farmers to shift toward practices that benefit the soil without sacrificing yield,” he says. “We need to test and use sustainable nutrient management practices. Poultry litter is an example of an alternative fertilizer source in the Southeast U.S. that provides macro- and micro-nutrients for the soil.”

However, information on the use and value of poultry litter in soybean–corn rotations is limited. To fill that gap, Farmaha is leading on-farm research funded by the South Carolina Soybean Board checkoff. 

“We want to determine what rates of poultry litter both optimize yield and restore soil health,” he explains. “New soil health tests allows us to study active fractions of nutrients in the soil, and we designed trials to identify measurable changes from the use of this organic fertilizer.”

He began the study in 2021, with plans to continue it for an additional two to four years to build a robust dataset from a variety of environments. Based on the first year of research, he plans to leverage this checkoff investment into additional support from other sources.

Comprehensive Trials

Farmaha designed this study to compare different ways of incorporating poultry litter into a soybean–corn rotation. 

  • Applying poultry litter to soybeans only, to observe the value to that crop and the residual effect for corn during the following season.
  • Applying fertilizer every season over two years, to both soybeans and corn, at the same rate, to study the cumulative effect.
  • Applying poultry litter to corn only to learn the direct effect on this crop.
  • Applying urea to corn to compare the two types of fertilizer.

Within each system, the trials will compare four poultry litter application rates: 1.5, 3, 4.5 and 6 tons per acre. In addition, each trial replication includes a control with no poultry litter or fertilizer applied.

“We surveyed extension agents in both South Carolina and North Carolina to get input on realistic rates to test,” Farmaha says. “In South Carolina, we heard recommendations up to 3 tons per acre, while in North Carolina recommendations can be made up to 6 tons per acre, and they asked us to include higher rates in this research, which published work has shown to accelerate building soil health.”

He notes that the nutrient value of poultry litter varies depending on its source. Broiler chickens, laying hens and turkeys all receive different feed, which is reflected in the litter. Other factors include bedding proportion and type, use of caked droppings of primarily waste versus the whole house litter including bedding, poultry growth stage, moisture content, litter handling system and storage time. To control these variables, a single broiler farmer supplied all the litter for the study, and it was tested for nutrient value before being applied.

Farmaha recommends applying poultry litter three to four weeks before planting. However, because this trial included so many small plots, his team had to apply the litter with small buckets, which was easier to do once the plants emerged. 

In 2021, the team conducted trials at four on-farm locations and two Clemson research stations. They planted soybean in 2021 and corn at these locations in 2022. In 2022, they established four new soybean sites, and they plan to plant corn in these fields in 2023. The various locations provide a variety of soil types and environments throughout South Carolina. Baseline soil tests taken at the beginning of the study will help show future changes in soil composition. 

Farmer and South Carolina Soybean Board member Racheal Sharp hosts one of the trial locations near Allendale. With fertilizer prices soaring, she is interested in the results. She and her father, who farm together, already plan their crop rotation to use nutrients from previous crops. This study will help them figure out how poultry litter best fits their system. Fertilizer prices increased dramatically in late 2021 and early 2022, but the cost of litter increased less than inorganic fertilizers.

Complex Results

According to past research, poultry litter can improve soil characteristics, such as aggregate stability, infiltration and organic matter content. It can also increase the availability of soil nutrients, including carbon, nitrogen, phosphorus, calcium and magnesium. 

“Despite using the same treatment structure for the study, the responses in the first year varied between fields,” Farmaha reports. “We are digging into variables like soil type and management system to better understand them as the research continues.”

While he didn’t see many crop and yield differences between the soybean trials in 2021, by mid-season in 2022, they observed some differences in crop growth in corn. Data from multiple years will be critical to forming recommendations related to poultry litter application and updating NRCS 590 Nutrient Management Conservation Practice Standards.

“Most research looking at soil health anticipates long-term soil changes,” Farmaha says. “In this study, we hope to observe measurable short-term changes that will encourage farmers to consider changing their practices.”

As he gathers initial results, he plans to add even more real-world complexity to this study. At a Clemson University Research and Education Center site, he hopes to follow the crop with a cover crop in the fall of 2022, conditions permitting. This will also impact nutrient availability and soil health.

“Our goal is to offer multiple options to farmers,” Farmaha says. “Profit margins are small, and they need data to determine what they can incorporate into their system.”

Published: Oct 10, 2022

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.