A new study shows that applying manure to crop fields by means of shallow disk injection into the soil, rather than traditional surface broadcast, significantly reduces estrogens in surface runoff.
Conducted by researchers in Penn State’s College of Agricultural Sciences, the study suggests that manure-application methods can be used to control the mobilization potential of estrogens and points to opportunities for protecting downstream water quality.
The research also investigated how manure-application methods affected runoff of total dissolved phosphorus and dissolved organic carbon. Researchers found that transport rates of those nutrients, to a lesser degree, also were lower after manure injection than after surface broadcast.
The application of livestock manure to agricultural fields provides essential nutrients for crops and adds organic matter to soils. However, manure also introduces emerging contaminants to the environment, including the natural estrogens 17 alpha-estradiol, 17 beta-estradiol, estrone and estriol, according to Heather Gall, assistant professor of agricultural and biological engineering.
The researchers used manure from dairy cattle, but estrogens are a component in the waste stream of not only dairy, but all livestock and humans. Although this study focused on ubiquitous natural estrogens, synthetic estrogens also can affect water quality, including ethinylestradiol, the active ingredient in birth control pills or synthetic androgens such as trenbolone, often given as ear implants to beef cattle.
“The method of animal manure application can influence the availability of nutrients and estrogens to runoff water,” said lead researcher Odette Mina, a recent doctoral degree graduate. “Several studies have shown the potential benefits of shallow disk injection for reducing phosphorus and nitrate transport in surface runoff compared to surface broadcasting. Our research demonstrated significantly reduced estrogen transport in runoff from shallow disk injection plots relative to surface broadcast plots.”
This research took place at the Kepler Farm plots located at the Russell E. Larson Agricultural Research Center in Rock Springs, near Penn State’s University Park campus. The site consists of 12 hydrologically isolated plots which direct surface runoff from each plot downslope through PVC pipes to huts near the plots. The huts are equipped with tipping buckets that measure the surface runoff flowrate and allow researchers to collect flow-weighted samples to analyze the nutrients and contaminants in the runoff.
Researchers saw a striking difference between estrogen loads and concentrations in runoff following precipitation events, Mina pointed out. When manure was injected into the soil, estrogens were far less likely to leave the field.
A rainfall event that occurred two days after manure was applied caused a really big movement of estrogens, carbon and phosphorus from the surface-broadcast plots, said Mina.
“But that same event was not enough to even trigger runoff from the plots that had undergone shallow disk injection of manure. That first flush washed off really high concentrations of phosphorus and estrogens relative to the entire rest of the study, but there was nothing from the shallow disk injection plots,” said Mina.
More research on the impacts of manure injection is planned. In a follow-on study, Gall said she wants to be sure keeping estrogens out of surface runoff doesn’t result in the contaminants leaching into groundwater.
“There potentially could be some trade-offs with groundwater quality, so by doing the shallow disk injection you could be promoting more nutrient and estrogen loss into groundwater, perhaps causing localized concerns for people pulling their water from wells,” Gall said.
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