Top two inset photos on this page courtesy of USDA‐NRCS When making decisions about what to do, people often have to weigh the potential trade‐offs. Taking a prescription drug can have side effects, buying a large vehicle often comes with larger gas bills, mittens are warmer than gloves, but we lose our dexterity. There are trade‐offs in managing agroecosystems, too. Farmers use fertilizer to maximize yields, but nutrients may runoff into surface waterways. Herbicides control weeds but can affect non‐target crops and other organisms. Recognizing the potential for trade‐offs or unintended impacts when managing crops and livestock is important. Sometimes unintended consequences are minor, whereas others have a large impact. Some impacts may be detected immediately while others develop over time. Researchers, consultants, and farmers are generally aware of the potential for trade‐offs to their management practices but may be able to improve their ability to detect, assess, and mitigate trade‐offs by learning about what others have done.

Unintended Consequences of No‐till Agriculture No‐till farming, where fields are not plowed between plantings, is suggested as a soil conservation practice in many regions. No‐till improves soil health by reducing erosion and building organic matter and can also reduce runoff of fertilizers to waterways. While the loss of particulate nutrients is reduced, no‐till agriculture can actually contribute to an increase in soluble phosphorus (P) leaching from farm fields. A recent article in the Journal of Environmental Quality (http://bit.ly/2F6htRJ) examines the unintended consequences of conservation practices on soluble P loads coming from watersheds draining into the western Lake Erie basin. The research was a collaboration from the U.K. Centre for Ecology & Hydrology, University of Arkansas, Heidelberg University (Tiffin, OH), the USDA‐ARS, and the International Plant Nutrition Institute. Lake Erie has a long history of water quality degradation from excessive phosphorus (P) inputs. In the 1960s and 1970s, algae issues led first to stricter point source discharge regulations; later, in the 1980s, conservation tillage and no‐till systems began to be promoted as a way to manage the problem. Initially, increased adoption of conservation tillage appeared to add to the water quality improvement achieved largely through point source controls. However, Helen Jarvie, a hydrochemist at the U.K. Centre for Ecology & Hydrology, says, “In the last 15 years, there has been a decline in lake water quality, with increases in algal blooms in the western basin, which has been linked to a rise in the more ecologically available soluble form of phosphorus.” This decline in water quality was well documented in 2014 when a toxic algal bloom in Lake Erie led the city of Toledo, OH to issue a “do not drink” advisory to over 400,000 residents. Jarvie and colleagues analyzed Heidelberg University's 40‐year daily water quality data from three major rivers that drain into western Lake Erie. They determined there was an increase in runoff associated with precipitation patterns but determined this alone was not responsible for the increase in soluble P. “This shift in land management [to no‐till], along with less incorporation into the soil of broadcast fertilizer applications, can increase losses of soluble P during rainfall‐induced runoff events and may also have been compounded by an increase in the installation of systematic subsurface drainage,” Jarvie says. Subsurface drainage, or tiles, can rapidly transport the soluble P from farm fields to streams and rivers. The long‐term data also revealed that there was a steep increase in soluble P runoff after 2002, so this unintended effect of no‐till agriculture was slow to become a noticeable problem in these systems.

Pathogens vs. Emissions The emission of noxious and greenhouse gases are another trade‐off to many agronomic production practices. Equipment releases carbon dioxide, cattle are a source of methane, and manure is a problem for anyone with livestock. While there are many potential sources of emissions, one that was recently published in the Journal of Environmental Quality (http://bit.ly/2HgYX9X) focuses on emissions from broiler houses. Poultry houses are known to be a source of ammonia emissions, but according to Kyoung Ro, a research environmental engineer for USDA‐ARS, there have been some “contradictory reports” on emission rates during downtime in between flocks. During this time, some managers will windrow the litter, which is a mixture of poultry excreta, spilled feed, feathers, and bedding materials such as wood shavings and straw, for re‐use. Windrowing, or partial composting, creates high temperatures in the litter that reduce pathogens. The reduction in pathogens makes it less likely that diseases or infections will spread to a subsequent flock in the same broiler house. Because of the uncertainty in emission rates, Ro and colleagues conducted a study comparing windrowed and non‐windrowed broiler houses. • Trade‐offs associated with management of agroecosystems range can have negative consequences on the environment.

• Trade‐offs to management practices may not be consistent across allecosystems due to differences in soils, climate, or other factors.

• When solving one problem creates another, management practices may need to be adapted to minimize negative impacts. The study compared two broiler houses, one in which litter was windrowed after a flock and one which was not treated. They measured ammonia (NH 4 ) and nitrous oxide (N 2 O) emissions. Ammonia emissions contribute to regional acidification and eutrophication, and N 2 O is a greenhouse gas with greater warming potential than carbon dioxide. Researchers found that both NH 4 and N 2 O emissions were greater when litter was windrowed. The team also analyzed litter samples for the presence of bacteria, and while levels were very low in the control house, pathogens were not detected in the windrowed samples. While the increased temperatures reduce pathogens in the litter, this practice comes with the trade‐off of greater emissions. For broiler producers, there is no simple, cost‐effective, solution to reduce both pathogens and emissions.

Resolving Conflicting Data Through research studies like these, trade‐offs can be identified and even quantified. However, as Ro pointed out, there is often conflicting data surrounding trade‐offs to management practices. In some situations, there is a great deal of data available, which can be useful for performing a meta‐analysis. While the reasons for soluble P loss in the Lake Erie watershed are now understood, this does not mean that all no‐till systems will respond in the same way. Because the effects of no‐till agriculture on P loss were unresolved, researchers conducted a meta‐analysis of P loss and published their results in the Journal of Environmental Quality (http://bit.ly/2Cn9pJ5). SSSA member Lixin Wang, an Assistant Professor in the Department of Earth Sciences at Indiana University–Purdue University Indianapolis, and co‐authors used data from a range of soil types, wide geographic area, and time since implementation in their meta‐analysis. In this study, they found soluble P loss to be greater in no‐till compared with conventional tillage systems. The meta‐analysis also revealed conditions under which this soluble P loss was increased. Soluble P loss is typically greater in dry climates or drought years and increases with time since no‐till was implemented. These effects of time and climate help to explain why not all research would find soluble P loss associated with no‐till agriculture. Using the meta‐analysis approach may help to identify trade‐offs of other management practices as well, especially when existing studies are not reaching the same conclusion. However, Wang points out that data availability can limit the application of meta‐analyses since researchers need many existing studies to perform this analysis.