With water quality in the Chesapeake Bay suffering from excess nutrients, and with fish populations in rivers such as the Susquehanna experiencing gender skewing and other reproductive abnormalities, understanding how to minimize runoff of both nutrients and endocrine-disrupting compounds from farm fields after manure applications is a critical objective for agriculture, according to The Pennsylvania State University.
A new study by researchers in Penn State's College of Agricultural Sciences found that applying manure to crop fields by means of shallow disk injection into the soil rather than traditional surface broadcast significantly reduced the level of estrogen in surface runoff.
This finding suggests that manure application methods can be used to control the mobilization potential of estrogen and points to opportunities for protecting downstream water quality, the researchers said.
The research, published this month in Agriculture, Ecosystems & Environment, also investigated how manure application methods affected runoff of total dissolved phosphorus and dissolved organic carbon. The researchers found that transport rates of those nutrients also were lower, to a lesser degree, after manure injection than after surface broadcast.
Earlier findings from the study, which was conducted from October 2014 through the summer of 2015, were published in the Journal of Environmental Quality in November 2016. The research sampled 10 surface runoff events from 12 research plots — six with each application method — after the fall application of manure.
The application of livestock manure to agricultural fields provides essential nutrients for crops and adds organic matter to soils. However, manure also introduces 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, such as ethinylestradiol, the active ingredient in birth control pills, or synthetic androgens such as trenbolone, which is often given to beef cattle via ear implants.
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. These factors include 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.
"The method of animal manure application can influence the availability of nutrients and estrogens to runoff water," Mina said. "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 flow rate and allow researchers to collect flow-weighted samples to analyze the nutrients and contaminants in the runoff.
The 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.
"We had a rainfall event that happened two days after the manure was applied. It wasn't a big rainfall event — (just) 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. However, "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."
Farmers have been slow to adopt shallow disk manure injection, Gall pointed out, and that is mostly due to the high cost of new injection equipment. The method is compatible with no-till agriculture, she added, and has the added benefit of causing less odor.
Before she can recommend that all farmers transition to injecting manure, however, Gall intends to do more research. In a follow-on study being planned now, she wants to be sure that 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 explained.