Accounting for the risks of phosphorus losses through tile drains in a phosphorus index

One size does not fit all: Toward regional conservation practice guidance to reduce phosphorus loss risk in the Lake Erie watershed

Agricultural phosphorus (P) losses to surface water bodies remain a global eutrophication concern, despite the application of conservation practices on farm fields. Although it is generally agreed upon that the use of multiple conservation practices ("stacking") will lead to greater improvements to water quality, this may not be cost effective to farmers, reducing the likelihood of adoption. At present, wholesale recommendations of conservation practices are given; however, the application of specific conservation practices in certain environments (e.g., no-till with surface application, cover crops) may not be effective and can even lead to unintended consequences. In this paper, we present the Lake Erie watershed as a case study. The Lake Erie watershed contains regions with unique physical geographies that include differences in climate, soil, topography, and land use, which have implications for both P transport from agricultural fields and the efficacy of conservation practices in mitigating P losses. We define major regions within the Lake Erie watershed where common strategies for conservation practice implementation are appropriate, and we propose a five-step plan for bringing regionally tailored, adaptive, and cost-conscious conservation practice into watershed planning. Although this paper is specific to the Lake Erie watershed, our framework can be transferred across broader geographic regions to provide guidance for watershed planning.

Sources and subsurface transport of dissolved reactive phosphorus in a semiarid, no-till catchment with complex topography

The subsurface transport of dissolved reactive phosphorus (DRP) from artificially drained agricultural fields can impair water quality, especially in no-till fields. The distribution of soil P in the wheat (Triticum aestivum L.)-dominated Palouse region in the inland U.S. Pacific Northwest varies greatly due to its steep and complex topography, and a legacy (∼130 yr) of excessive soil erosion and deposition processes. The primary goal of this research was to better understand the magnitude and temporal dynamics of DRP export from an artificial drain line and the variability of subsurface DRP leaching within a long-term, no-till field. Dissolved reactive P in drain line effluent was monitored across three water years. Large intact soil cores were extracted at contrasting field locations (toe and top slope positions) to measure DRP leachate concentration and relative P sorption. Drain line DRP concentration was predominantly >0.05 mg L^-1 and often exceeded 0.1 mg L^-1 during winter and early spring. Mean leachate DRP levels were significantly higher in toe slope cores than in top slope cores (0.11 and 0.02 mg L^-1 , respectively). Saturated hydraulic conductivity varied widely across cores and was not correlated with leachate DRP concentration. All soil cores exhibited high P sorption potential, even under conditions of preferential flow. These findings suggest that much of the DRP transport in these landscapes is derived from P hotspots located in toe slope positions. Application of soil P fertilizer amounts in variable rates that account for spatial variability in P transport may minimize P enrichment and subsequent leaching in these locations.

A Novel Approach for Detecting Unique Variations among Infectious Bacterial Species in Endocarditic Cardiac Valve Vegetation

Infectious endocarditis (IE) remains one of the deadliest heart diseases with a high death rate, generally following thrombo-embolic events. Today, therapy is based on surgery and antibiotic therapy. When thromboembolic complications in IE patients persist, this is often due to our lack of knowledge regarding the pathophysiological development and organization of cells in the vegetation, most notably the primordial role of platelets and further triggered hemostasis, which is related to the diversity of infectious microorganisms involved. Our objective was to study the organization of IE vegetations due to different bacteria species in order to understand the related pathophysiological mechanism of vegetation development. We present an approach for ultrastructural analysis of whole-infected heart valve tissue based on scanning electron microscopy and energy-dispersive X-ray spectroscopy. Our approach allowed us to detect differences in cell organization between the analyzed vegetations and revealed a distinct chemical feature in viridans Streptococci ones. Our results illustrate the benefits that such an approach may bring for guiding therapy, considering the germ involved for each IE patient.

Dissolved phosphate concentrations in Iowa shallow groundwater

Regional groundwater phosphorus (P) concentrations are rarely reported, and it is important to develop a better understanding of background concentrations in shallow groundwater to help develop strategies to mitigate environmental risks. In this study, results collected from 17 different Iowa-based studies conducted from 2006 to 2019 and a total of 210 discrete locations of water table dissolved phosphate (DPO₄ ^3- ) measurements are summarized (a) to assess the occurrence, range, and statistical distribution of groundwater DPO₄ ^3- concentrations in Iowa and (b) to evaluate statewide patterns of DPO₄ ^3- concentrations related to land use or land cover and landscape position. The DPO₄ ^3- concentrations ranged from 0.02 to 1.56 mg L^-1 and averaged 0.15 ± 0.19 mg L^-1 with a median value of 0.10 mg L^-1 (95% confidence interval of 0.08-0.11 mg L^-1 ). Although minor variations were observed among land cover class and landscape position, concentrations exhibited uniformity across the state, likely attesting to the legacy of P from historical agricultural management. Median concentrations are higher than typical water quality criteria used to assess risk to surface water systems, implying that simply discharging groundwater DPO₄ ^3- to streams, rivers, and lakes would be sufficient to cause environmental degradation.

Spatiotemporal variations of nitrogen and phosphorus in a clay plain hydrological system in the Great Lakes Basin

Nutrient imbalance in groundwater and surface water resources can have severe implications on human and aquatic life, including contamination of drinking water sources and the degradation of ecosystems. A field-based watershed-scale study was completed to investigate nutrient dynamics and hydrologic processes in an agriculturally-dominant clay plain system within the Great Lakes Basin. Spatial and temporal variations of nitrogen and phosphorus were examined by sampling groundwater and surface water regularly over a period of one year (June 2017 to July 2018) for nutrients including nitrate, soluble reactive phosphorus, total dissolved phosphorus and total reactive phosphorus. Nitrate transport from surrounding agricultural land to surface water was intensified with an increase in precipitation events in spring and early winter and phosphorus transport to surface water was increased during freeze-thaw cycles in the winter. The results are pertinent to the improvement of current nutrient and water management policies in clay plain systems where nutrient imbalances in surface water are a concern.

Phosphorus loss assessment tools: a review of underlying concepts and applicability in cold climates

Identifying critical source areas (CSAs) of a watershed by phosphorus (P) loss assessment tools is essential for optimal placement of beneficial management practices (BMPs) to address diffuse P pollution. However, lack of significant progress in tackling diffuse P pollution could be, in part, associated with inefficacy of P loss assessment tools for accurately identifying CSAs. Phosphorus loss assessment tools have been developed to simulate P loss from the landscape where runoff is mainly driven by rainfall events. Therefore, they may underperform in cold climates where the land is often frozen during winter and runoff is dominated by snowmelt. This paper (i) reviews the strengths and weaknesses of current P loss assessment tools and their underlying assumptions in simulating soil P dynamics and P transfer to runoff, and (ii) highlights a number of challenges associated with modeling P transfer from agricultural land to surface waters in cold climates. Current P loss assessment tools do not appear to fully represent hydrological and biogeochemical processes responsible for P loss from CSAs, particularly in cold climates. Effort should be made to develop P loss assessment tools that are capable of considering P dynamics through the landscape as a result of abiotic perturbations that are common in cold climates, predicting runoff and P movement over frozen/partially frozen soils, and considering material-P connectivity between landscape and surface waters. Evaluating P loss assessment tools with water quality data is necessary to ensure such modifications result in improved identification of CSAs.

Evaluating Hydrologic Response in Tile-Drained Landscapes: Implications for Phosphorus Transport

Phosphorus (P) loss in agricultural discharge has typically been associated with surface runoff; however, tile drains have been identified as a key P pathway due to preferential transport. Identifying when and where these pathways are active may establish high-risk periods and regions that are vulnerable for P loss. A synthesis of high-frequency, runoff data from eight cropped fields across the Great Lakes region of North America over a 3-yr period showed that both surface and tile flow occurred year-round, although tile flow occurred more frequently. The relative timing of surface and tile flow activation was classified into four response types to infer runoff-generation processes. Response types were found to vary with season and soil texture. In most events across all sites, tile responses preceded surface flow, whereas the occurrence of surface flow prior to tile flow was uncommon. The simultaneous activation of pathways, indicating rapid connectivity through the vadose zone, was seldom observed at the loam sites but occurred at clay sites during spring and summer. Surface flow at the loam sites was often generated as saturation-excess, a phenomenon rarely observed on the clay sites. Contrary to expectations, significant differences in P loads in tiles were not apparent under the different response types. This may be due to the frequency of the water quality sampling or may indicate that factors other than surface-tile hydrologic connectivity drive tile P concentrations. This work provides new insight into spatial and temporal differences in runoff mechanisms in tile-drained landscapes.

Contribution of Overland and Tile Flow to Runoff and Nutrient Losses from Vertisols in Manitoba, Canada

This study quantified the contributions of overland and tile flow to total runoff (sum of overland and tile flow) and nutrient losses in a Vertisolic soil in the Red River valley (Manitoba, Canada), a region with a cold climate where tile drainage is rapidly expanding. Most annual runoff occurred as overland flow (72-89%), during spring snowmelt and large spring and summer storms. Tile drains did not flow in early spring due to frozen ground. Although tiles flowed in late spring and summer (33-100% of event flow), this represented a small volume of annual runoff (10-25%), which is in stark contrast with what has been observed in other tile-drained landscapes. Median daily flow-weighted mean concentrations of soluble reactive P (SRP) and total P (TP) were significantly greater in overland flow than in tile flow ( < 0.001), but the reverse pattern was observed for NO-N ( < 0.001). Overland flow was the primary export pathway for both P and NO-N, accounting for >95% of annual SRP and TP and 50 to 60% of annual NO-N losses. Data suggest that tile drains do not exacerbate P export from Vertisols in the Red River valley because they are decoupled from the surface by soil-ice during snowmelt, which is the primary time for P loss. However, NO-N loading to downstream water bodies may be exacerbated by tiles, particularly during spring and summer storms after fertilizer application.

Tillage and Fertilizer Management Effects on Phosphorus Runoff from Minimal Slope Fields

Phosphorus fertilization can increase P losses in surface runoff, but limited information is available for fields with <2% slopes in the US Midwest. Our objectives were to determine the effects of tillage-fertilizer placement (no-till-broadcast, strip till-broadcast; or strip till-deep placement, -15-cm subsurface band) and fertilizer rate applied in the fall (0, 52, or 90 kg PO ha yr) on runoff P concentrations and loads in fields with <2% slopes near Pesotum, IL, during fall and spring simulation runoff events, and to measure corn ( L.) and soybean [ (L.) Merr.] grain yield. Across four simulated runoff events, deep placement reduced dissolved reactive P (DRP) loads by 69 to 72% compared with the broadcast treatments. A tillage-fertilizer placement × P rate interaction showed that DRP and total P (TP) concentrations remained low when P was deep placed, regardless of P rate, whereas concentrations increased with increasing P rate for the broadcast treatments, but no differences existed for bioavailable P (BAP) (α = 0.05). At one site, rainfall simulation in the spring versus fall increased runoff volumes but sharply decreased BAP concentrations. During fall runoff simulations, deep placement reduced TP loads, and greater TP loads occurred with the 90- than the 52-kg PO ha yr rate. Similarly, when P was broadcast in the fall, DRP and TP concentrations were greater than deep-placed P, but no treatment differences occurred in the spring. Deep banding P and K did not reduce crop yield but reduced runoff losses of P from flat fields compared with broadcast P applications, particularly at high rates of P application.

Supply and Transport Limitations on Phosphorus Losses from Agricultural Fields in the Lower Great Lakes Region, Canada

Phosphorus (P) mobilization in agricultural landscapes is regulated by both hydrologic (transport) and biogeochemical (supply) processes interacting within soils; however, the dominance of these controls can vary spatially and temporally. In this study, we analyzed a 5-yr dataset of stormflow events across nine agricultural fields in the lower Great Lakes region of Ontario, Canada, to determine if edge-of-field surface runoff and tile drainage losses (total and dissolved reactive P) were limited by transport mechanisms or P supply. Field sites ranged from clay loam, silt loam, to sandy loam textures. Findings indicate that biogeochemical processes (P supply) were more important for tile drain P loading patterns (i.e., variable flow-weighted mean concentrations ([]) across a range of flow regimes) relative to surface runoff, which trended toward a more chemostatic or transport-limited response. At two sites with the same soil texture, higher tile [] and greater transport limitations were apparent at the site with higher soil available P (STP); however, STP did not significantly correlate with tile [] or P loading patterns across the nine sites. This may reflect that the fields were all within a narrow STP range and were not elevated in STP concentrations (Olsen-P, ≤25 mg kg). For the study sites where STP was maintained at reasonable concentrations, hydrology was less of a driving factor for tile P loadings, and thus management strategies that limit P supply may be an effective way to reduce P losses from fields (e.g., timing of fertilizer application).

Vertical Stratification of Soil Phosphorus as a Concern for Dissolved Phosphorus Runoff in the Lake Erie Basin

During the re-eutrophication of Lake Erie, dissolved reactive phosphorus (DRP) loading and concentrations to the lake have nearly doubled, while particulate phosphorus (PP) has remained relatively constant. One potential cause of increased DRP concentrations is P stratification, or the buildup of soil-test P (STP) in the upper soil layer (<5 cm). Stratification often accompanies no-till and mulch-till practices that reduce erosion and PP loading, practices that have been widely implemented throughout the Lake Erie Basin. To evaluate the extent of P stratification in the Sandusky Watershed, certified crop advisors were enlisted to collect stratified soil samples (0-5 or 0-2.5 cm) alongside their normal agronomic samples (0-20 cm) ( = 1758 fields). The mean STP level in the upper 2.5 cm was 55% higher than the mean of agronomic samples used for fertilizer recommendations. The amounts of stratification were highly variable and did not correlate with agronomic STPs (Spearman's = 0.039, = 0.178). Agronomic STP in 70% of the fields was within the buildup or maintenance ranges for corn ( L.) and soybeans [ (L.) Merr.] (0-46 mg kg Mehlich-3 P). The cumulative risks for DRP runoff from the large number of fields in the buildup and maintenance ranges exceeded the risks from fields above those ranges. Reducing stratification by a one-time soil inversion has the potential for larger and quicker reductions in DRP runoff risk than practices related to drawing down agronomic STP levels. Periodic soil inversion and mixing, targeted by stratified STP data, should be considered a viable practice to reduce DRP loading to Lake Erie.

Modified APEX model for Simulating Macropore Phosphorus Contributions to Tile Drains

The contribution of macropore flow to phosphorus (P) loadings in tile-drained agricultural landscapes remains poorly understood at the field scale, despite the recognized deleterious impacts of contaminant transport via macropore pathways. A new subroutine that couples existing matrix-excess and matrix-desiccation macropore flow theory and a modified P routine is implemented in the Agricultural Policy Environmental eXtender (APEX) model. The original and modified formulation were applied and evaluated for a case study in a poorly drained field in Western Ohio with 31 months of surface and subsurface monitoring data. Results highlighted that a macropore subroutine in APEX improved edge-of-field discharge calibration and validation for both tile and total discharge from satisfactory and good, respectively, to very good and improved dissolved reactive P load calibration and validation statistics for tile P loads from unsatisfactory to very good. Output from the calibrated macropore simulations suggested median annual matrix-desiccation macropore flow contributions of 48% and P load contributions of 43%, with the majority of loading occurring in winter and spring. While somewhat counterintuitive, the prominence of matrix-desiccation macropore flow during seasons with less cracking reflects the importance of coupled development of macropore pathways and adequate supply of the macropore flow source. The innovative features of the model allow for assessments of annual macropore P contributions to tile drainage and has the potential to inform P site assessment tools.

Assessing Coastal Plain Risk Indices for Subsurface Phosphorus Loss

Phosphorus (P) Index evaluations are critical to advancing nutrient management planning in the United States. However, most assessments until now have focused on the risks of P losses in surface runoff. In artificially drained agroecosystems of the Atlantic Coastal Plain, subsurface flow is the predominant mode of P transport, but its representation in most P Indices is often inadequate. We explored methods to evaluate the subsurface P risk routines of five P Indices from Delaware, Maryland (two), Virginia, and North Carolina using available water quality and soils datasets. Relationships between subsurface P risk scores and published dissolved P loads in leachate (Delaware, Maryland, and North Carolina) and ditch drainage (Maryland) were directionally correct and often statistically significant, yet the brevity of the observation periods (weeks to several years) and the limited number of sampling locations precluded a more robust assessment of each P Index. Given the paucity of measured P loss data, we then showed that soil water extractable P concentrations at depths corresponding with the seasonal high water table (WEP) could serve as a realistic proxy for subsurface P losses in ditch drainage. The associations between WEP and subsurface P risk ratings reasonably mirrored those obtained with sparser water quality data. As such, WEP is seen as a valuable metric that offers interim insight into the directionality of subsurface P risk scores when water quality data are inaccessible. In the long term, improved monitoring and modeling of subsurface P losses clearly should enhance the rigor of future P Index appraisals.

Edge-Of-Field Evaluation of the Ohio Phosphorus Risk Index

The Phosphorus Index (PI) has been the cornerstone for phosphorus (P)-based management and planning over the past twenty years, yet field-scale evaluation of many state PIs has been limited. In this study, P loads measured in surface runoff and tile discharge from 40 agricultural fields in Ohio with prevailing management practices were used to evaluate the Ohio PI. Annual P loads were highly variable among fields (dissolved reactive P: 0.03-4.51 kg ha, total P: 0.03-6.88 kg ha). Both measured annual dissolved reactive P ( = 0.36, < 0.001) and total P ( = 0.25, < 0.001) loads were significantly related to Ohio PI score. The relationship between measured load and PI score substantially improved when averaged annual field values were used (dissolved reactive P: = 0.71, total P: = 0.73), indicating that the Ohio PI should be utilized to evaluate average annual risk of P loss, rather than as an annual risk tool. Comparison between the Ohio PI and other established local and national metrics resulted in large differences in potential P management recommendations for the monitored fields. In the near term, revision of Ohio PI risk categories and management recommendations using local P loading thresholds is needed. To meet the minimum criteria for state PI tools, future research efforts should focus on using measured field data (i) to incorporate new input factors (i.e., P application timing and leaching potential) into the Ohio PI, and (ii) to calibrate and validate the Ohio PI to provide better P risk assessments and management recommendations.

Characterization of fly ash ceramic pellet for phosphorus removal

Phosphorus has been recognized as a leading pollutant for surface water quality deterioration. In the Midwestern USA, subsurface drainage not only provides a pathway for excess water to leave the field but it also drains out nutrients like nitrogen (N) and phosphorus (P). Fly ash has been identified as one of the viable materials for phosphorus removal from contaminated waters. In this study, a ceramic pellet was manufactured using fly ash for P absorption. Three types of pellet with varying lime and clay proportions by weight (type 1: 10% lime + 30% clay, type 2: 20% lime + 20% clay, and type 3: 30% lime + 10% clay) were characterized and evaluated for absorption efficiency. The result showed that type 3 pellet (60% fly ash with 30% lime and 10% clay) had the highest porosity (14%) and absorption efficiency and saturated absorption capacity (1.98 mg P/g pellet) compared to type 1 and 2 pellets. The heavy metal leaching was the least (30 μg/L of chromium after 5 h) for type 3 pellet compared to other two. The microcosmic structure of pellet from scanning electron microscope showed the type 3 pellet had the better distribution of aluminum and iron oxide on the surface compared other two pellets. This result indicates that addition of lime and clay can improve P absorption capacity of fly ash while reducing the potential to reduce chromium leaching.

Applicability of models to predict phosphorus losses in drained fields: a review

Most phosphorus (P) modeling studies of water quality have focused on surface runoff loses. However, a growing number of experimental studies have shown that P losses can occur in drainage water from artificially drained fields. In this review, we assess the applicability of nine models to predict this type of P loss. A model of P movement in artificially drained systems will likely need to account for the partitioning of water and P into runoff, macropore flow, and matrix flow. Within the soil profile, sorption and desorption of dissolved P and filtering of particulate P will be important. Eight models are reviewed (ADAPT, APEX, DRAINMOD, HSPF, HYDRUS, ICECREAMDB, PLEASE, and SWAT) along with P Indexes. Few of the models are designed to address P loss in drainage waters. Although the SWAT model has been used extensively for modeling P loss in runoff and includes tile drain flow, P losses are not simulated in tile drain flow. ADAPT, HSPF, and most P Indexes do not simulate flow to tiles or drains. DRAINMOD simulates drains but does not simulate P. The ICECREAMDB model from Sweden is an exception in that it is designed specifically for P losses in drainage water. This model seems to be a promising, parsimonious approach in simulating critical processes, but it needs to be tested. Field experiments using a nested, paired research design are needed to improve P models for artificially drained fields. Regardless of the model used, it is imperative that uncertainty in model predictions be assessed.

Phosphorus transport in agricultural subsurface drainage: a review

Phosphorus (P) loss from agricultural fields and watersheds has been an important water quality issue for decades because of the critical role P plays in eutrophication. Historically, most research has focused on P losses by surface runoff and erosion because subsurface P losses were often deemed to be negligible. Perceptions of subsurface P transport, however, have evolved, and considerable work has been conducted to better understand the magnitude and importance of subsurface P transport and to identify practices and treatments that decrease subsurface P loads to surface waters. The objectives of this paper were (i) to critically review research on P transport in subsurface drainage, (ii) to determine factors that control P losses, and (iii) to identify gaps in the current scientific understanding of the role of subsurface drainage in P transport. Factors that affect subsurface P transport are discussed within the framework of intensively drained agricultural settings. These factors include soil characteristics (e.g., preferential flow, P sorption capacity, and redox conditions), drainage design (e.g., tile spacing, tile depth, and the installation of surface inlets), prevailing conditions and management (e.g., soil-test P levels, tillage, cropping system, and the source, rate, placement, and timing of P application), and hydrologic and climatic variables (e.g., baseflow, event flow, and seasonal differences). Structural, treatment, and management approaches to mitigate subsurface P transport-such as practices that disconnect flow pathways between surface soils and tile drains, drainage water management, in-stream or end-of-tile treatments, and ditch design and management-are also discussed. The review concludes by identifying gaps in the current understanding of P transport in subsurface drains and suggesting areas where future research is needed.

Enhanced nitrate and phosphate removal in a denitrifying bioreactor with biochar

Denitrifying bioreactors (DNBRs) are an emerging technology used to remove nitrate-nitrogen (NO) from enriched waters by supporting denitrifying microorganisms with organic carbon in an anaerobic environment. Field-scale investigations have established successful removal of NO from agricultural drainage, but the potential for DNBRs to remediate excess phosphorus (P) exported from agricultural systems has not been addressed. We hypothesized that biochar addition to traditional woodchip DNBRs would enhance NO and P removal and reduce nitrous oxide (NO) emissions based on previous research demonstrating reduced leaching of NO and P and lower greenhouse gas production associated with biochar amendment of agricultural soils. Nine laboratory-scale DNBRs, a woodchip control, and eight different woodchip-biochar treatments were used to test the effect of biochar on nutrient removal. The biochar treatments constituted a full factorial design of three factors (biochar source material [feedstock], particle size, and application rate), each with two levels. Statistical analysis by repeated measures ANOVA showed a significant effect of biochar, time, and their interaction on NO and dissolved P removal. Average P removal of 65% was observed in the biochar treatments by 18 h, after which the concentrations remained stable, compared with an 8% increase in the control after 72 h. Biochar addition resulted in average NO removal of 86% after 18 h and 97% after 72 h, compared with only 13% at 18 h and 75% at 72 h in the control. Biochar addition also resulted in significantly lower NO production. These results suggest that biochar can reduce the design residence time by enhancing nutrient removal rates.

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.

Nutrient loss in leachate and surface runoff from surface-broadcast and subsurface-banded broiler litter

Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff compared with conventional surface broadcast application. Little research has been conducted to determine the effects of surface broadcast application and subsurface banding of litter on nutrients in leachate. Therefore, a field experiment was conducted to determine the effects of subsurface band application and surface broadcast application of poultry litter on nutrient losses in leachate. Zero-tension pan and passive capillary fiberglass wick lysimeters were installed in situ 50 cm beneath the soil surface of an established tall fescue ( Schreb.) pasture on a sandy loam soil. The treatments were surface broadcast and subsurface-banded poultry litter at 5 Mg ha and an unfertilized control. Results of the rainfall simulations showed that the concentrations of PO-P and total phosphorus (TP) in leachate were reduced by 96 and 37%, respectively, in subsurface-banded litter treatment compared with the surface-applied litter treatment. There was no significant difference in PO-P concentration between control and subsurface-banded litter treatment in leachate. The trend in the loading of nutrients in leachate was similar to the trend in concentration. Concentration and loading of the nutrients (TP, PO-P, NH-N, and NO-N) in runoff from the subsurface-banded treatment were significantly less than for the surface-applied treatment and were similar to those from control plots. These results show that, compared with conventional surface broadcast application of litter, subsurface band application of litter can greatly reduce loss of P in surface runoff and leachate.

Evaluation of phosphorus indices after twenty years of science and development

The P Index was proposed as a nutrient management tool in 1992 and has been implemented as such for the past decade. However, lack of water quality improvement in agricultural watersheds and discrepancies in P loss ratings between P indices have raised questions about continued use of the P Index. In response to these concerns, a symposium was held as part of the 2011 ASA, CSSA, SSSA annual meetings. This symposium produced a special collection of seven papers describing the role of P indices in P management, evaluation of P indices, new models for assessing P loss, methods to improve P indices, and changes in producer behavior resulting from P Index use. The objectives of this introductory paper are to provide background on the P Index concept, overviews of the special collection papers, and recommendations for future P Index evaluation and development research. The papers in this special collection conclude that P indices can provide accurate assessments of P loss but must be evaluated appropriately. Evaluation will require compiling large regional P loss datasets at field and small watershed scales. Simulation models may be used to generate P loss estimates; however, models must be calibrated and validated to ensure their accuracy. Further development of P indices will require coordinated regional efforts to identify common P Index frameworks and standardized interpretations. Stringent P Index evaluations will expand the utility of P indices for critical source area identification and strategic best management practice implementation by regulatory, education, and scientific communities alike.