UNIVERSITY PARK, Pa. — A new study by researchers in Penn State’s College of Agricultural Sciences shows that applying manure to crop fields by means of shallow disk injection significantly reduces estrogens in surface runoff.
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 findings suggest that manure-application methods can be used to control the mobilization potential of estrogens and points to opportunities for protecting downstream water quality.
About the research
The study, which was conducted from October 2014 through the summer of 2015, sampled 10 surface runoff events from 12 research plots — six with each application method — after the fall application of manure.
While manure provides essential nutrients for crops and adds organic matter to soils, it 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.
What are estogens
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 natural estrogens, synthetic estrogens also can affect water quality, such as ethinylestradiol, the active ingredient in birth control pills or synthetic androgens such as trenbolone, often given as ear implants to beef cattle.
Many factors influence the fate and transport of these manure-borne hormones, explained lead researcher Odette Mina, a recent doctoral degree graduate in agricultural and biological engineering, including the type of manure applied, the rate and timing of application, the method and history of application, as well as natural drivers such as hydrologic processes and biogeochemical cycling.
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,” said Mina.
What they found
Researchers saw a striking difference between estrogen loads and concentrations in runoff following precipitation events, Mina added.
When manure was injected into the soil, estrogens were far less likely to leave the field.
“We had a rainfall event that happened two days after the manure was applied — it wasn’t a big rainfall event, a typical storm that you would expect every year — and it caused a really big movement of estrogens, carbon and phosphorus from the surface-broadcast plots,” she said.
“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.”
Adoption of shallow-disk manure injection among farmers has been slow, Gall said, and that mostly results from the high cost of new injection equipment. But the method is compatible with no-till agriculture and has the added benefit of causing less odor.
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