University of Arkansas Division of Agriculture researchers hope to determine the feasibility of using poultry litter as a fertilizer for rice.
Poultry litter contains concentrations of nitrogen, phosphorus and potassium, the three major nutrients for which Division of Agriculture scientists make recommendations, said Nathan Slaton, assistant professor of crop, soil and environmental sciences and director of soil testing for the Arkansas Agricultural Experiment Station.
“There are two components to our study,” he said. “One specifically addresses nitrogen. The other looks at phosphorus and potassium.”
In both studies, the performance of poultry litter is compared to standard inorganic fertilizers. Urea is used for nitrogen, triple super phosphate for phosphorus and muriate of potash for potassium. The litter is used in two forms: fresh litter right out of the chicken house, and pelletized litter.
“We don't know the actual fertilizer value of the nutrients in the litter,” Slaton said. “So the total nitrogen rates we used for litter in 2003 were much higher than the rates for urea.”
The litter was applied by incorporating it into the soil before planting. This is the same practice used for triple super phosphate and muriate of potash, but urea is typically applied after the rice has emerged, just before flooding the fields.
Slaton said all soils are nitrogen deficient, so adding nitrogen fertilizer produces a visually obvious response. “We found that as we applied higher rates of litter, the rice seedlings grew faster and were darker green before flooding at the five-leaf stage,” he said. Urea was applied preflood in the comparison plots, according to standard practice. “A week after flooding, the urea plots were green and growing like mad.”
From that point on, the rice fertilized preplant with the highest rates of litter did not keep up with the rice fertilized even with the lowest rates of preflood urea.
Bobby Golden, a UA graduate student working with Slaton, measured nitrogen uptake at mid-season by the rice in these test plots. The urea plots showed a “fertilizer use efficiency” — how much of the applied nitrogen is taken up by the plants — of 50 percent to 80 percent. That's well within the range UA soil scientists Rick Norman and Chuck Wilson documented in earlier soil fertility research.
In the poultry litter plots, the uptake averaged only 5 percent to 10 percent at mid-season. However, by heading, the nitrogen use efficiency of litter nitrogen had increased to 15 percent to 30 percent, Golden said.
“This indicates that although an appreciable amount of the litter nitrogen is lost when the field is flooded, some of the nitrogen is slowly released during the entire growing season,” Slaton said. “Preplant applications of litter must be supplemented with inorganic nitrogen fertilizer before flooding, but the need for midseason nitrogen may be reduced or even eliminated.
“Even though we applied much more nitrogen in the poultry litter plots, we got far less nitrogen in the plants when flooding at the five-leaf stage, which is the standard management practice,” Slaton said.
“Under our current rice management system, litter is just not an efficient source of nitrogen,” he said. “I think we can improve that, possibly by changes in management practices or by amending the litter with some process that keeps the nitrogen in a useable form that the rice can take up for a longer period.”
The story is very different for poultry litter used as a source of phosphorus and potassium. “Preliminary data suggests litter is equal in efficiency to the common inorganic sources of these two nutrients,” Slaton said.
He said research is needed to see if moving poultry litter to Delta farms is cost efficient. On the basis of fertilizer use, however, Slaton said it appears best to base the use of litter as a rice fertilizer on its value as a source of phosphorus and potassium rather than its value for nitrogen.
Kristofor Brye, assistant professor of applied soil physics, said the long-term use of poultry litter might have benefits for the health of soils in the Delta.
“I believe that after three to five years of using poultry litter, we'll be able to measure changes in organic matter, soil carbon, water-holding capacity and other characteristics,” Brye said. “I think we'll see similar changes whether we're using fresh or palletized litter.”
Brye is studying the soil physics associated with Slaton's research of adding poultry litter to Delta soils. “Within five years I expect to see improvements in the condition of Delta soils, where litter is used annually, that will lead to improved yields,” he said.
Fred Miller is science editor for the Arkansas Agricultural Experiment Station. e-mail: [email protected].