Arthur L. Allen

Evaluating the Success of Phosphorus Management from Field to Watershed

Studies have demonstrated some P loss reduction following implementation of remedial strategies at field scales. However, there has been little coordinated evaluation of best management practices (BMPs) on a watershed scale to show where, when, and which work most effectively. Thus, it is still difficult to answer with a degree of certainty, critical questions such as, how long before we see a response and where would we expect to observe the greatest or least response? In cases where field and watershed scales are monitored, it is not uncommon for trends in P loss to be disconnected. We review case studies demonstrating that potential causes of the disconnect varies, from competing sources of P at watershed scales that are not reflected in field monitoring to an abundance of sinks at watershed scales that buffer field sources. To be successful, P-based mitigation strategies need to occur iteratively, involve stakeholder driven programs, and address the inherent complexity of all P sources within watersheds.

Soil controls of phosphorus in runoff: Management barriers and opportunities

Kleinman, P. J. A., Sharpley, A. N., Budda, A. R., McDowell, R. W. and Allen, A. L. 2011. Soil controls of phosphorus in runoff: Management barriers and opportunities. Can. J. Soil Sci. 91: 329-338. The persistent problem of eutrophication, the biological enrichment of surface waters, has produced a vast literature on soil phosphorus (P) effects on runoff water quality. This paper considers the mechanisms controlling soil P transfers from agricultural soils to runoff waters, and the management of these transfers. Historical emphases on soil conservation and control of sediment delivery to surface waters have demonstrated that comprehensive strategies to mitigate sediment-bound P transfer can produce long-term water quality improvements at a watershed scale. Less responsive are dissolved P releases from soils that have historically received P applications in excess of crop requirements. While halting further P applications to such soils may prevent dissolved P losses from growing, the desorption of P from soils that is derived from historical inputs, termed here as “legacy P”, can persist for long periods of time. Articulating the role of legacy P in delaying the response of watersheds to remedial programs requires more work, delivering the difficult message that yesterdays sinks of P may be todays sources. Even legacy sources of P that occur in low concentration relative to agronomic requirement can support significant loads of P in runoff under the right hydrologic conditions. Strategies that take advantage of the capacity of soils to buffer dissolved P losses, such as periodic tillage to diminish severe vertical stratification of P in no-till soils, offer short-term solutions to mitigating P losses. In some cases, more aggressive strategies are required to mitigate both short-term and legacy P losses.

Using Flue Gas Desulfurization Gypsum to Remove Dissolved Phosphorus from Agricultural Drainage Waters

High levels of accumulated phosphorus (P) in soils of the Delmarva Peninsula are a major source of dissolved P entering drainage ditches that empty into the Chesapeake Bay. The objective of this study was to design, construct, and monitor a within-ditch filter to remove dissolved P, thereby protecting receiving waters against P losses from upstream areas. In April 2007, 110 Mg of flue gas desulfurization (FGD) gypsum, a low-cost coal combustion product, was used as the reactive ingredient in a ditch filter. The ditch filter was monitored from 2007 to 2010, during which time 29 storm-induced flow events were characterized. For storm-induced flow, the event mean concentration efficiency for total dissolved P (TDP) removal for water passing through the gypsum bed was 73 ± 27% confidence interval (α = 0.05). The removal efficiency for storm-induced flow by the summation of load method was 65 ± 27% confidence interval (α = 0.05). Although chemically effective, the maximum observed hydraulic conductivity of FGD gypsum was 4 L s(-1), but it decreased over time to <1 L s(-1). When bypass flow and base flow were taken into consideration, the ditch filter removed approximately 22% of the TDP load over the 3.6-yr monitoring period. Due to maintenance and clean-out requirements, we conclude that ditch filtration using FGD gypsum is not practical at a farm scale. However, we propose an alternate design consisting of FGD gypsum-filled trenches parallel to the ditch to intercept and treat groundwater before it enters the ditch.

Effect of direct incorporation of poultry litter on phosphorus leaching from coastal plain soils

Management of poultry litter on the Delmarva Peninsula is critical to reducing phosphorus losses to the Chesapeake Bay. New poultry litter incorporation technologies have shown promise at reducing phosphorus losses, but their effectiveness has not been tested in this environmentally sensitive region. This study evaluates subsurface leaching losses of three litter application methods, including surface broadcast, surface broadcast with disking, and subsurface litter incorporation with a novel litter incorporator developed by the USDA Agricultural Research Service. Cube-shaped soil lysimeters (61 × 61 × 61 cm [24 × 24 × 24 in]) were extracted from high phosphorus (P) (Mehlich-3 P is greater than 500 mg kg−1) agricultural soils on the University of Maryland Eastern Shore Research Farm near Princess Anne, Maryland, and were subjected to two rainfall simulation events that were separated by 11 semiweekly soaking-type irrigation events. The average cumulative total phosphorus loss was highest for the subsurface litter incorporation method (0.48 kg ha−1 [0.43 lb ac−1]) and was lowest for the no litter control (0.19 kg ha−1 [0.17 lb ac−1]). Particulate P loss among manure treatments ranged from 58% to 64% of total P loss. Total phosphorus losses were strongly correlated to total phosphorus concentration in the leachate (coefficient of determination [r2] ≥ 0.84), indicating availability of P in applied litter to be the primary control of P in leachate. Soil properties also impacted P leaching losses, with the soils possessing a higher sand content and having a shallower depth to the sandy subsoil, yielding higher cumulative total P losses (0.64 kg ha−1 [0.57 lb ac−1]). Although the subsurface litter incorporator increased total P leaching losses, a concern on the Delmarva Peninsula, opportunity exists to modify the subsurface incorporator design using zone tillage, potentially reducing the leaching losses.

Managing manure for sustainable livestock production in the Chesapeake Bay Watershed

Manure presents one of the greatest challenges to livestock (dairy and beef cattle, swine, poultry, equine, sheep, llamas, etc.) operations in the Chesapeake Bay Watershed, serving both as resource and liability. The Chesapeake Bay is threatened by excessive nutrient loadings, and, according to the US Environmental Protection Agency (USEPA), manure is the source of 18% of the nitrogen and 27% of the phosphorus entering the Chesapeake Bay annually (figure 1) (Chesapeake Bay Program 2010). Developing economical, practical, and effective manure management options for livestock producers will not only contribute to the restoration of the Chesapeake Bay, but will also provide a model for other areas where water quality and livestock production objectives must be balanced. The 166,000 km2 (64,000 mi2) Chesapeake Bay Watershed is home to 3.2 million animal units (animal unit = 454 kg [1,000 lbs] of livestock) generating roughly 36 million t (40 million tn) of livestock manure per year. In comparison, the 14 million humans who call the Chesapeake Bay Watershed home generate 3.6 million t (4 million tn) of waste annually (Brosch 2010; Blankenship 2005). The livestock manure contains approximately 259,000 t (285,000 tn) of nitrogen and 70,000 t (77,000 tn) of phosphorus. Most manure is…

Phosphorus leaching from agricultural soils of the delmarva peninsula, USA.

Leaching of phosphorus (P) mobilizes edaphic and applied sources of P and is a primary pathway of concern in agricultural soils of the Delmarva Peninsula, which defines the eastern boundary of the eutrophic Chesapeake Bay. We evaluated P leaching before and after poultry litter application from intact soil columns (30 cm diameter × 50 cm depth) obtained from low- and high-P members of four dominant Delmarva Peninsula soils. Surface soil textures ranged from fine sand to silt loam, and Mehlich-3 soil P ranged from 64 to 628 mg kg. Irrigation of soil columns before litter application pointed to surface soil P controls on dissolved P in leachate (with soil P sorption saturation providing a stronger relationship than Mehlich-3 P); however, strong relationships between P in the subsoil (45-50 cm) and leachate P concentrations were also observed ( = 0.61-0.73). After poultry litter application (4.5 Mg ha), leachate P concentrations and loads increased significantly for the finest-textured soils, consistent with observations that well-structured soils have the greatest propensity to transmit applied P. Phosphorus derived from poultry litter appeared to contribute 41 and 76% of total P loss in leachate from the two soils with the finest textures. Results point to soil P, including P sorption saturation, as a sound metric of P loss potential in leachate when manure is not an acute source of P but highlight the need to factor in macropore transport potential to predict leaching losses from applied P sources.

Phosphorus and nitrogen leaching before and after tillage and urea application.

Leaching of nutrients through agricultural soils is a priority water quality concern on the Atlantic Coastal Plain. This study evaluated the effect of tillage and urea application on leaching of phosphorus (P) and nitrogen (N) from soils of the Delmarva Peninsula that had previously been under no-till management. Intact soil columns (30 cm wide × 50 cm deep) were irrigated for 6 wk to establish a baseline of leaching response. After 2 wk of drying, a subset of soil columns was subjected to simulated tillage (0-20 cm) in an attempt to curtail leaching of surface nutrients, especially P. Urea (145 kg N ha) was then broadcast on all soils (tilled and untilled), and the columns were irrigated for another 8 wk. Comparison of leachate recoveries representing rapid and slow flows confirmed the potential to manipulate flow fractions with tillage, albeit with mixed results across soils. Leachate trends in the finer-textured soil suggest that tillage impeded macropore flow and forced greater matrix flow. Despite significant vertical stratification of soil P that suggested tillage could prevent leaching of P via macropores from the surface to the subsoil, tillage had no significant impact on P leaching losses. Relatively high levels of soil P below 20 cm may have served as the source of P enrichment in leachate waters. However, tillage did lower losses of applied urea in leachate from two of the three soils, partially confirming the studys premise that tillage would destroy macropore pathways transmitting surface constituents to the subsoil.

A protocol for conducting rainfall simulation to study soil runoff.

Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hr after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been prewetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.

Transport of dissolved trace elements in surface runoff and leachate from a Coastal Plain soil after poultry litter application

The application of poultry (Gallus gallus domesticus) litter to agricultural soils may exacerbate losses of trace elements in runoff water, an emerging concern to water quality. We evaluated trace elements (arsenic [As], mercury [Hg], selenium [Se], and zinc [Zn]) in surface runoff and leachate from an agricultural soil with and without poultry litter application. Litter from a commercial operation was applied by three methods—broadcast application, subsurface placement, and broadcast application followed by disking—to no-till soils with a history of receiving litter. Soil monolith lysimeters (61 by 61 by 61 cm)(24 by 24 by 24 in) were extracted from each of the treatments and subjected to rainfall simulation (1 hour, 61 mm h−1 [2.4 in hr−1]) 15 and 42 days after litter application. Broadcasting poultry litter significantly increased concentrations (mg L−1) and loads (g ha−1) of As and Zn in runoff during the first event relative to other application methods. Notably, incorporating litter, either by disking after broadcasting or by subsurface placement, lowered As and Zn in runoff to near background levels by the second event, and there were no significant differences in As and Zn between any of the treatments. While Hg and Se were detected in runoff, they likely derived from edaphic sources as they were not detected in the litter nor did they differ significantly between treatments. Results point to poultry litter as a temporary source of some trace elements to runoff. This source can be readily controlled by adjusting application method.

Nitrogen Fate in Drainage Ditches of the Coastal Plain after Dredging

Drainage ditches are a key conduit of nitrogen (N) from agricultural fields to surface water. The effect of ditch dredging, a common practice to improve drainage, on the fate of N in ditch effluent is not well understood. This study evaluated the effect of dredging on N transport in drainage ditches of the Delmarva Peninsula. Sediments from two ditches draining a single field were collected (0-5 cm) to represent conditions before and after dredging. Sediments were packed in 10-m-long recirculating flumes and subjected to a three-phase experiment to assess the sediments role as a sink or source of ammonium (NH4) and nitrate (NO3). Under conditions of low initial NH4-N and NO3-N concentrations in flume water, sediment from the undredged ditch released 113 times more NO3-N to water than did sediment from the dredged ditch. When flume water was spiked with NH4-N and NO3-N to simulate increases in N concentrations from drainage and runoff from adjacent fields, NO3-N in flume water increased during 48 h compared with the initial spiked concentration, while NH4-N decreased. These simultaneous changes were attributed to nitrification, with 23% more NO3-N observed in flume water with undredged ditch sediment compared with dredged ditch sediment. Replacing the N-spiked water with deionized water resulted in two times more NO3-N released from the undredged ditch sediment than the dredged ditch sediment. These results suggest that ditch sediments could represent significant stores of N and that dredging could greatly affect the ditch sediments ability to temporarily assimilate N input from field drainage.