[Image above] Chicken litter is good fertilizer but crumbles easily, making it difficult to transport. How can we make it harder? Credit: Corey Pudhorodsky, Flickr (CC BY-NC-ND 2.0)
Americans are crazy for chicken—and not just the new Popeye’s sandwich.
Since 1960, the amount of chicken consumed per capita in the United States has risen enormously, from about 28 pounds per year to 96 pounds in more recent years. In contrast, red meat dropped perceptibly, from 133 pounds to 111 pounds. And due to the African swine fever outbreak in pig herds across China last year, consumption of chicken is expected to increase even more on a global scale.
This massive consumption of chicken shows “clear potential to be a biostratigraphic marker species of the Anthropocene,” a recent article on how leftover chicken bones will affect the geological record argues.
Millions of bones are not the only way chickens leave their mark on the environment. A more immediate effect is chicken litter, a mixture of chicken excreta, spilled feed, feathers, and material used as bedding in chicken operations.
In the past, chicken litter was used mainly for feeding ruminants, such as cattle and sheep. However, ever since some countries like Australia started banning the practice in response to bovine spongiform encephalopathy (“mad cow disease”), this residue is increasingly used as organic fertilizer instead due to its composition rich in nitrogen, potassium, and phosphorus, among other nutrients.
To use chicken litter as fertilizer, farmers turn the waste into dried pellets. They do so for two big reasons:
- Nutrients in the waste stay integrated until application
- Controlled nutrient release decreases the possibility of contaminating groundwater
In theory, another reason for turning chicken litter into pellets is that it makes transporting the waste easier. However, “problems related to the physical properties are still significant when dealing with OMF [granular organomineral fertilizers], considering that the organic matter tends to considerably disintegrate during transportation and storage, after the formation of the granule,” researchers write in a recent paper.
The researchers, from the Brazilian Agricultural Research Corporation and Federal University of Bahia, decided to investigate different binder materials to improve the mechanical properties of such fertilizers—and the binders they investigated were ceramic.
The five ceramic additives analyzed included three bentonite compositions, kaolinite, and magnesium oxide. Bentonite is an absorbent aluminum phyllosilicate clay; kaolinite is a layered silicate clay mineral. Researchers manually mixed four different concentrations of the additive materials (0.5%, 1%, 2%, and 3% (w/w)) with monoammonium phosphate (35%) and then added them to chicken litter to create granular discs with diameters of 40 cm.
Visually, the granules did not show significant differences. Hardness, however, varied between samples depending on the additive used and its concentration.
There was no significant difference in hardness among the bentonites analyzed, and the kaolinite also did not increase hardness overly much. On the other hand, magnesium oxide at a concentration of 3% exhibited significant improvement, increasing granule hardness by up to four times when compared to controls (without ceramic additives).
“This result was already expected, since positive results were obtained in other studies that used magnesium oxide to increase the hardness of granulated drugs and fertilizers,” the researchers write. “This characteristic is attributed to the fact that, when added in small concentrations to the salt fertilizer powder mixture, the magnesium oxide is able to suppress water for long periods of time, avoiding the disintegration of the granule even under conditions of high air humidity and temperature.”
“In addition, the presence of magnesium oxide positively influences the integration of the fertilizer when in its production involves the reaction of phosphoric acid and ammonia,” they add.
The researchers also conducted dissolution tests with the additives to see if nutrient release was affected. They concluded that increased hardness did not affect the dissolution, but “it is necessary to evaluate larger concentrations to see if the behavior repeats itself under new conditions and check agronomic efficiency of these fertilizers.”
The paper, published in International Journal of Applied Ceramic Technology, is “The effect of different ceramic materials to improve hardness of organomineral fertilizer granules” (DOI: 10.1111/ijac.13226).