1a. Objectives (from AD-416):
The overall objective of our research is to sustain agriculture and water resources in the northeastern US. Our basic research provides fundamental information on processes (chemical, physical, hydrologic), linking agricultural management with water resources. Our applied research advances nutrient management practices and strategies that balance production and agroecological services, helping agriculture to adapt to emerging water resource issues and, ultimately, promoting resilient agroecosystems that can respond to long-term challenges occurring at scales beyond the farm gate. Specific objectives are: (1) Describe and quantify processes controlling agriculturally related environmental contaminants (nutrients, trace metals, and sediments). (2) Adapt and develop management practices and strategies that farmers can use to reduce the environmental impacts of agriculturally derived contaminants. (3) Conduct watershed scale research to understand the long-term impacts of changing management and climate on water resources.
1b. Approach (from AD-416):
Research will span the four major physiographic provinces of the Chesapeake Bay watershed, relying upon core sites in the Atlantic Coastal Plain (Manokin watershed, MD), Appalachian Piedmont (Conewago watershed, PA), Appalachian Valley and Ridge (Mahantango Creek watershed, PA and Spring Creek watershed, PA), and Allegheny Plateau (Anderson Creek watershed, PA) (Figure 1). Research emphases will vary across these provinces, reflecting issues that are of current management or scientific relevance as well as constraints imposed by available resources (Figure 2). Our primary distinction is between the Atlantic Coastal Plain and upland physiographic regions, as hydrologic flow paths are dramatically different in these landscapes (subsurface flow is the dominant hydrologic pathway in the Atlantic Coastal Plain whereas overland and shallow lateral flows are the major pathways in the upland provinces). We have landowner contacts and research collaborators at all major (core) sites, and have a research infrastructure that enables routine measurement and chemical sampling of surface runoff, subsurface flow, and stream flow. When necessary, we move infrastructure from one location to another to provide a greater intensity of observations. We combine field observations with laboratory experiments in which greater control may be obtained over indirect variables. Our process-oriented research (Objective 1) involves observational and experimental studies, using parametric and nonparametric statistics to quantify temporal and spatial trends or to determine differences between management/land use, landscape units, and watershed components. Our applied research (Objectives 2 and 3) includes experimental studies, remote sensing and modeling. Experimentation involves a high degree of replication due to the inherent variability in processes impacting water quality. We have strong in-house statistical capability and, when necessary, consult with outside statisticians to ensure confidence in our findings.
3. Progress Report:
Laboratory studies were carried out to elucidate factors affecting nutrient and trace element fate and transport. We found that slow release N fertilizers lower ammonia losses after application. However, stabilized amine fertilizers had ammonia emissions that were equivalent to, or greater than conventional fertilizers. Mixing aragonite with urea exacerbated ammonia emissions. In separate studies, we found that P and As compete directly for binding sites on soils such that applying P to soil causes As to be released to leachate water. In column leaching studies, we found that that urea can leach through macropores under extreme leaching conditions, but that these conditions were rare. Urea losses in surface runoff amounted to less than 1 percent of applied urea. A combined runoff and leaching study of trace elements following poultry manure application revealed similarities in As and Zn transport with P transport. Elsewhere, a pedogenic model accurately predicted the presence of physical discontinuities in soils. Monitoring shallow groundwater above these discontinuities demonstrated their role in nutrient losses; shallow groundwater contained 60% of the nutrient loss in hillslope runoff. Initiated field projects to curtail off-site pollution. Trials in MD and PA with the ARS Subsurfer confirmed that subsurface placement of poultry manure lowers P loss in runoff, nearly expunges odor and ammonia-N emissions, and increases corn yield in some cases. However the Subsurfer sometimes increased nutrient leaching. To control P loss in groundwater, new gypsum curtains were installed on four MD farms where they lowered P concentrations in the drainage water by up to 90%. Projects were initiated to advance decision support systems. A network of watersheds was established across four ARS locations and across the Chesapeake Bay region. New protocols were developed to test the P Index. In addition, we implemented new hydrologic monitoring on eight farms in PA as part of the development of a daily decision support model that employs weather forecasts. Logistic regression models show the potential to reliably forecast runoff risk. Watershed-scale studies were initiated evaluate temporal and spatial trends in climate and water resources. Retrospective analyses of climate and hydrology in the Mahantango Creek (PA) watershed show that mean annual air temperature and precipitation increased from 1981 through 2010, while streamflow decreased. Nitrate and phosphate in stream water did not change over the 30 years, but pH dropped from 7 to 6, a major increase in watershed acidity. An historical land use database was developed (1998-2010) for more than 200 fields in the Mahantango Creek watershed. New monitoring of urea in the Manokin River watershed (MD) showed that urea concentrations in stream base flow were highest in poorly drained forested areas, whereas in storm flow, peak urea concentrations were highest in agricultural drainage ditches. Early findings suggest that total N load, rather than land applied urea, is the major cause of elevated urea in streams.
1. Managing the legacy of past management. During the past decade, there has been increasing awareness that the legacy of past management may be undermining watershed conservation measures intended to reduce nutrient losses from agriculture. ARS studies in the coastal plain and upland reaches of the Chesapeake Bay watershed highlight the role of past management in current water quality conditions and point to new solutions. In some cases, the effects of historical applications of nutrients may require many decades to reverse, unless creative measures to tackle legacy sources of nutrients are imposed. Results from this research are being used by ARS researchers at University Park, Pennsylvania to improve watershed models, develop new practices to remove legacy sources of nutrients from runoff waters, and educate watershed managers and the general public of the causes of water quality decline.
2. Urea fate and transport on the Atlantic Coastal Plain. There is growing global concern over urea, the most common form of commercial nitrogen (N) fertilizer, because it can promote toxic algal blooms in estuarine waters when it is present in relatively low concentrations. ARS researchers at University Park, Pennsylvania, partnering with colleagues from the University of Maryland Eastern Shore and Penn State University, evaluated urea fate and transport in field drainage, runoff, and stream water within an agricultural basin on Maryland’s Atlantic Coastal Plain, and showed that transfers of recently applied urea to runoff waters are highly unlikely under normal climatic conditions and proper nutrient management. Instead, stagnant water in small field ditches connected to N-rich groundwater can create ideal conditions for the microbial production of urea, which can then be flushed into local streams during the next rainfall event. These results refute the argument that the agricultural industry should restrict the use of manure, a “free” N source, and also switch to a different, more costly form of commercial N fertilizer to address urea pollution.
3. Reduced ammonia emissions with manure injection. The wide-spread adaption of no-till crop production has led to large reductions in soil erosion and associated nutrient losses, but losses of nitrogen from manure through ammonia volatilization can be high in the absence of incorporation by tillage. Low disturbance manure incorporation technologies were evaluated by ARS researchers at University Park, Pennsylvania. Shallow disk injection was shown to consistently reduce ammonia emission by over 90% with little disruption of the soil surface, but manure incorporation with a rolling-tine aerator was shown to consistently reduce ammonia losses only when the implement was configured to aggressively mix soil. Ammonia emission findings have been disseminated widely to farmers throughout the region through extension presentations and have influenced the development of interim NRCS practice standards for manure injection in Pennsylvania and other states in the Chesapeake Bay watershed.
4. Management of arsenic in applied litter is key to its control. Most to all of the broadcast-applied arsenic is lost in subsequent rainfall events, with the largest losses occurring in the first event following application. ARS researchers at University Park, Pennsylvania incorporated litter into soils with disk tillage resulted in lower losses of arsenic to surface runoff than did broadcasting litter, where arsenic in litter was left vulnerable to removal by runoff water. Disk tillage resulted in lower losses of arsenic to leachate than did subsurface application, which concentrated litter in below-ground pockets. Findings offer valuable insight into management options to minimize the off-site losses of arsenic from manure amended soils.
Buda, A.R., Kleinman, P.J., Feyereisen, G.W., Miller, D.A., Knight, P.G., Drohan, P.J., Bryant, R.B. 2013. Forecasting runoff from Pennsylvania landscapes. Journal of Soil and Water Conservation. 68(3): 183-196. DOI: 10.2489/jswc.68.3.185.