As a major poultry producing state, North Carolina has plenty of broiler litter, and university specialists are working to ensure litter is spread at best time and place. However, poultry litter isn’t always available when the crop needs it most.
In discussing land application of poultry manure, Stephanie Kulesza, assistant professor of nutrient management and animal waste at North Carolina State University, said poultry litter contains a variety of elements including bedding material, fresh feces and urine, spilled feed, feathers and water.
“It mineralizes more quickly than other organic nitrogen sources,” said Kulesza. “Because there’s a lot of uric acid in poultry litter, the mineralization (nitrogen availability) is much quicker after land application. There’s a lot more total nitrogen available compared to dairy manure.”
Due to its high uric acid content, poultry litter breaks down rapidly and becomes plant available. However, there’s also risk of ammonia volatilization immediately after land application.
“It’s a great fertilizer,” said Kulesza, “but there are also risks associated with loss because it’s rapidly available.”
With the application of any organic material, nitrogen in the material is mostly in the organic form and must undergo mineralization in order to become plant available.
Most producers apply poultry litter pre-plant, which can be a few months in advance up to immediately prior to planting. However, advance application is technically outside the manure application regulations of many states.
“Timing becomes an important factor,” said Kulesza. “Most litter is applied in spring. If we can give some people some flexibility, they’d appreciate it.”
When considering poultry litter as a nitrogen source, the goal is to avoid nitrogen application prior to crop needs. If nitrogen becomes available prior to crop needs, there’s a long period of potential loss in the soil. In the event of heavy rainfall, most of the nitrogen is washed away. But if nitrogen is applied apply too late and crop nitrogen needs aren’t met, yields may be reduced. Late application also leaves nitrogen in the field that will mineralize and potentially be lost.
The goal, and challenge, is to apply litter at the optimum time. Ideally, soil moisture is good in winter and drier toward spring, then the crop receives more moisture and warmth throughout summer. Kulesza said these conditions lead to continuous mineralization throughout the year.
Poultry litter is most often available for land application when crops aren’t growing. Photo by Sally Colby
During 2020, a particularly wet year, Kulesza found that producers who wanted to land apply manure had to adjust application schedules due to excess soil moisture. “In North Carolina, we have to apply waste to an actively growing crop within 30 days of breaking dormancy or within 30 days of planting,” she said. “But when the weather is unpredictable, it became hard to prioritize land application of manure when field conditions were optimum.”
Optimizing manure application meant delayed planting, so Kulesza wanted to know if there was an opportunity to plant during optimum field conditions and apply manure later. One issue is that manure is applied with large, heavy equipment, which can result in physical damage to plants and compaction, and chemical damage via ammonia. In many areas, manure is moved offsite for application. Scheduling manure application can be a challenge because hauling schedules are often full.
Kulesza wanted to learn whether reducing nitrogen loss and improved scheduling flexibility by applying in-season to maximize nitrogen efficiency would reduce the risk of loss and maintain nitrogen uptake. Physical damage to growing crops and potential yield loss were additional concerns.
A study was designed to determine the impact of in-season application of poultry litter on corn yield and quality. Researchers also assessed how different application timing and rate of litter application affected ammonia volatilization and nitrogen use efficiency.
The 2023-24 study was conducted at two North Carolina sites: one in the coastal plains and one in the Piedmont region. Each site had a different soil type. Broiler litter was topdressed by hand to determine chemical damage. Litter was applied at planting, V2 and V5. Application rates were 0, 2, 4, 8 and 16 tons/acre.
While Kulesza admits 16 tons/acre is excessive, her goal was to mimic over-application or a field breakdown where a load is dumped in one site. Researchers conducted soil tests, took plant tissue samples and imitated ammonia volatilization in a closed chamber. The expected result was more ammonia loss as the season progressed, temperatures became warmer and soil more moist.
“We applied manure when it wasn’t a great time to do so,” said Kulesza. “Soil was extremely wet. We waited a few days, then applied litter and planted the same day. Because of the intense soil moisture around planting, there was an increase in ammonia loss. This information could help reduce ammonia loss because we can apply when field conditions are optimum.”
Litter was spread normally, including over the plants, with no intentional exclusion of plants from the application area. Yield results showed there was not enough chemical damage to reduce yields, even at a rate of 16 tons/acre.
“We need nitrogen to mineralize, so we don’t want to apply so late that we miss the window to get it to the crop,” said Kulesza. “We didn’t see any differences in application timing in either site or site years. This could be a suitable method, assuming physical damage doesn’t result in yield reduction.”
When more nitrogen is applied, more nitrogen makes it to the grain. Kulesza saw an increase in grain protein with higher nitrogen application. However, there wasn’t a response based on application timing. There was sufficient nitrogen for high yields, even when it was applied at V5.
One test result showed a small increase in leaf tissue potassium, but Kulesza wasn’t sure why. In 2024, there was a drought at the beginning of year followed by heavy moisture. Kulesza postulated that plants had more time to accumulate potassium when it was applied at planting due to sufficient moisture at planting but isn’t convinced that’s the sole reason.
“At one site we saw higher ammonia loss due to poor field conditions,” said Kulesza. “This was part of the rationale of doing the study: when litter is applied when it’s too wet, it’s possible to drive off more nitrogen. This is one benefit of applying in better field conditions. We saw a potassium difference, but we aren’t quite sure why.
“The biggest takeaway is that there wasn’t a timing effect on grain yield or grain nitrogen uptake. Because of that, we didn’t see a negative impact on yield, timing or nitrogen use efficiency. Our next goal is to look at the physical aspects.”
by Sally Colby
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