With fertilizer prices rising, for the last year Nathan Slaton has been fielding many questions about the value of poultry litter.
“We've been studying the fertilizer value of poultry litter for five years, at least,” says the University of Arkansas associate professor and fertility specialist. “Good quality poultry litter is often analyzed at 60-60-60 (N, P205, K2O). For plants to grow, N and potassium are taken up in about the same amount. So there's a balance as far as N and potash. And that's a good thing.”
The problem is chicken litter phosphate is also available in large amounts. Plants take up much less phosphate than nitrogen and potash.
“When poultry litter is applied based on N fertilizer content, phosphate is most often oversupplied. That isn't necessarily a terrible thing in the short-term for eastern Arkansas. Most of the soils there require some phosphate or, in many cases, test low to medium.”
Being able to apply poultry litter at the recommended rates of P “is fine. And applying a bit extra to get the benefit of N is okay since we need to build the P levels in the soil a tad.”
That's the exact opposite of the situation in much of western Arkansas where poultry litter was applied for years on a continuous basis. Under that treatment, soil test P eventually accumulated to the point where it's now being implicated as a source of pollution for surface water.
Several years ago, University of Arkansas researchers agreed to develop a strategy to recommend how poultry litter should be used in eastern Arkansas in row crops. It was decided to go with a very conservative approach and base recommendations on phosphorus. So, if a crop has a recommendation for 60 units of P2O5, then litter should be applied to satisfy that rate.
“Then, we'd figure out how much of the N in that litter would contribute to the N recommendation for the crop.”
The studies first began with rice. “Obviously, Arkansas has a different row-crop agriculture than other states simply because of the large rice acreage. Rice demands different cultural practices like flooding.”
Many states claim 50 to 60 percent of the nitrogen in poultry litter is plant-available during the first year. If a ton of litter contains 60 total units of nitrogen, some 30 to 40 pounds of that would be credited towards the fertilizer nitrogen recommendations.
“We also began with rice because (chicken litter) is a great amendment for leveled fields. That practice is usually performed for several years in succession, at least until the productivity of the soil has been restored and producers can go back to applying only inorganic fertilizers.”
With rice, researchers found that the poultry litter nitrogen becomes available very quickly.
“But it can be too quick. By the time we get to the five-leaf stage, much of the N is in a nitrate form that is immediately lost when the field is flooded or the soil becomes saturated from rain. The rice research suggested 25 percent of N in poultry litter can be credited towards the pre-flood N recommendation.”
The researchers also looked at the P and K availability compared to inorganic fertilizers. In the tests, there was never a response to P and K.
However, the tissue analysis suggested that a pound of K2O in poultry litter is basically the same as a pound of K2O in muriate of potash fertilizer.
“In the grand scheme with rice, we suggested considering 100 percent of the P and K in the litter to be available and 25 percent of the N.”
More study is being done on chicken litter in wheat.
“That's been our most recent attempt. Unfortunately, our first year to work with litter in wheat was affected badly by the freeze last Easter.
“There isn't much data to talk about with much confidence.”
However, preliminarily, Slaton believes chicken litter is a good source of P and K for wheat. And it provides a bit of starter nitrogen in the fall.
“The main thing to figure out, since it's applied just before it turns cold, is how quickly the N in the litter is released to the wheat.”
When considering whether the price of chicken litter is competitive, Slaton adheres to a general rule: get the litter analyzed. There are differences in the integrator's diet mixes — Cargill versus Tyson versus Townsends — and that can influence litters' nutrient content and fertilizer value.
“For us to be able to use the litter in a responsible manner, we need to know exactly what we're dealing with. That's why the litter needs to be analyzed.
“How much N, P2O5 and K2O equivalence is there in a ton of moist litter? Once that information is available, I don't think how quickly the N will break down is as critical.
“If you take 20 sources of poultry and study how quickly the N breaks down, there is some variation.
“But, like most recommendations, you find the middle point and base the recommendations from there. That's where we get the 50 to 60 percent figure for plant available N in the first year. You can't overemphasize the importance of getting litter analyzed.”
In some areas, chicken houses may be cleaned out after every flock of broilers. Such litter includes a larger amount of bedding material and usually less nutrient per ton.
Research shows that if three flocks have been run through the house, the litter should be “very good.”
And the three-flock quality doesn't change much compared to litter from six or seven house-loads.
Pelleted litter is an important component to consider — something the aforementioned rice research did. “We compared pelletized to fresh litter and found, in the rice fields, their N fertilizer values were identical.”
More recently, Slaton and colleagues have been doing research in northwest Arkansas on bermudagrass.
“This past year, we measured ammonia volatilization losses from the different inorganic N fertilizers and pelleted litter. We'd hypothesized there would be considerable ammonia coming off the pelleted litter.”
In fact, the study showed that wasn't the case.
“We ran a separate study looking at fresh versus pelleted litter. There was simply much less ammonia volatilization losses from the pelleted.”
That could certainly be considered a plus when applying it to row-crop soils.
“The next question to answer is why we found very little ammonia volatilization from the pelleted litter and how consistent that will be. I have some ideas, but I'm not exactly sure why that's happening.”
Slaton and colleagues also addressed the pelleted versus fresh issue years ago “when we first began recommending poultry litter for precision-graded soils.”
Fresh litter is much cheaper than pelleted. “Pelleted litter generally sells for $110 to $130 per ton. I've heard fresh litter can be found for $30 to $40 per ton.”
But the pelleted is much easier to handle. Producers must weigh cost versus ease-of-handling.
There have been claims that pelleted litter contains less water than fresh.
“That's generally true — the pelleted litter we've analyzed has 10 to 12 percent moisture. Fresh litter straight from the house usually has 20 to 24 percent moisture.
“Additionally, nutrient analysis performed on litter is expressed on a moist basis so that you know the nutrient content of the litter as it will be applied.
“However, the difference in moisture doesn't equal $80, or more.
“When doing the research, we compared the litter on a dry weight basis, taking the moisture factor out.
“What we found in the graded soils is that a pound of chicken litter is a pound of chicken litter. It doesn't matter whether it's straight from the chicken or run through a pelletizer. I suspect that when we finish the study on nutrient value, the same will be found.”
Impetus and magic
Several years ago, USDA issued a press release supporting the use of manures on legume crops. “When I first heard that I thought, ‘that's really curious since legumes make their own nitrogen.’ But the more I thought about and read up on it, there was a lot of merit there.”
Legumes do make their own nitrogen. If there's nitrogen in the soil, “the plant may be a bit lazy but once the soil N is used, the legume will start fixing its own.
“Basically they were saying apply manures based on a crop's phosphorus needs. That way you won't run into situations where litter is being applied at excessive rates and leads to buildups of excessive soil P and water quality concerns.”
So Slaton and colleagues began looking at the idea in soybeans, overseeing 10 to 12 studies over the last four years. The litter was applied at the same rate as the P and K in Triple Super Phosphate and muriate potash.
The only difference between the soybean treatments is that poultry litter supplies some nitrogen while the P and K fertilizers used contained no nitrogen.
A short, two-year study at the Keiser, Ark., research station showed no response to P and K and no yield differences between the litter and P and K fertilizers.
“As a researcher, I was kind of disappointed to see that. I was hoping that litter held more magic — a positive response that could not be explained by P and K fertilizer value. We also did a similar test on a silt loam in Stuttgart, Ark., and had the same findings. Of all the studies at Pine Tree, Ark., up until this past year there was no response, either.”
But that isn't the whole story and some magic does lurk in the litter. “We've had three tests in grower fields on the west side of Crowley's Ridge in Poinsett County. These are rice/soybean-producing soils.”
Poinsett County is renowned in the state: if a nutrient deficiency shows up, “it tends to be there first. Boron troubles first showed up there. There have also been deficiencies of P and K in rice and soybeans. There have been zinc deficiencies in rice.”
The three litter studies in Poinsett County fields showed no response to P and K. However, in all three of the studies, the poultry litter outyielded both inorganic fertilizer treatments and unfertilized checks by about 10 bushels per acre.
“So maybe the magic is unlocked only in certain areas. For some soils, the litter seems to stimulate additional yield.
“We're not sure why litter increased yields at those three sites, but something positive is going on. The benefit could be a response to N, another plant-essential nutrient that is present in the litter, or some other less obvious reason. We'd like to pursue that more vigorously if growers are interested and funding is available.”