Can the risk of P contamination of water be reduced? This lesson, developed from presentations given at Waste to Worth 2015 gives learners the opportunity to:
- Identify how current and previous management can affect phosphorus risk,
- Recognize various tools to determine phosphorus risk in different situations, and
- Discover one method of decreasing potential water pollution from phosphorus loss.
Background
Deanna Osmond – P Loss Assessments Verses Water Quality Outcomes
Phosphorus indices provide relative loss ratings that then have a corresponding management response. Because most state Phosphorus Indices are qualitative it is not clear how the relative loss rating corresponds to actual phosphorus inputs into the receiving water and how the receiving water would react to these additions. Even with qualitative Phosphorus Indices, unless the water resource has a specific Total Maximum Daily Load, it is not clear how losses correspond to water quality outcomes. These issues will be discussed in the context of the 590 Natural Resources Conservation Standard for nutrient management. Full proceedings are available here.
Legacy Phosphorus
Andrew Sharpley – How Legacy Nutrients Affect Farm Conservation Measures
Terrestrial phosphorus legacies encompass prior nutrient and land management activities that have built up soil phosphorus to levels that exceed crop requirements and modified the connectivity between terrestrial phosphorus sources and fluvial transport. River and lake phosphorus legacies encompass a range of processes that control retention and remobilization of P, and these are linked to water and sediment residence times. We provide case studies that highlight the major processes and varying timescales, over which legacy phosphorus continues to contribute phosphorus to receiving waters and undermine restoration efforts, and discuss how these phosphorus legacies could be managed in future conservation programs. We have learned that conservation practices that we implement on the land to trap phosphorus runoff, can eventually transition from sinks to sources of phosphorus. Full proceedings are available here.
Heidi Waldrip – Effects of Long-Term Poultry Litter Application on Phosphorus Distribution
Very few studies have investigated the long-term effects of manure or litter application on soil P distribution: almost no data exist on manure impacts on calcium-associated organic P in soil. Sequential fractionation techniques, coupled with phosphatase hydrolysis, have allowed for greater understanding of manure/litter effects on soil P distribution and transformation. A fairly standardized designation is separation of extracted P into labile P (H2O- and NaHCO3-P), moderately labile P (NaOH-P; assumed to be associated with amorphous Al/Fe oxides and organic matter), and stable P (HCl-P; assumed to be Ca-associated phosphates). Incubation of the extracted fractions with excess P hydrolyzing enzymes enables further characterization of organic P as phosphomonoester-like, nucleotide-like, phytate-like, or non-hydrolyzable organic P.
The specific objectives of this study were to investigate effects of long-term poultry litter application and land-use type (cultivated, grazed/ungrazed improved pasture, native rangeland) on soil P distribution in watershed-scale plots. The goal of this work is an improved understanding of how litter impacts P cycling and availability in these agronomically important calcareous soils. Full proceedings are available here.
Tools to Assess Phosphorus Risk
Andrew Sharpley – Identify and Synthesize Methods to Refine Phosphorus Indices from Three Regional Indexing Efforts
Despite the success of the Phosphorus Index concept in state-level nutrient management planning strategies as part of the NRCS 590 Standard, there remain concerns about the effectiveness of the Indexing approach for attaining water quality goals. Different versions of the Phosphorus Index have emerged to account for regional differences in soil types, land management, climate, physiographic and hydrologic controls, manure management strategies, and policy conditions. Along with this development, differences in Phosphorus Index manure management recommendations under relatively similar site conditions have also emerged. To date, we have learned that the individual projects with slightly differing objectives have shown there to be a paucity of field measured runoff, against which to reliably compare Index performance. Thus, several off-the shelf and pre-calibrated models (e.g., APEX) were tested to provide adequate phosphorus runoff information to validate Indices. Use of off-the-shelf models can provide unreliable estimates of phosphorus runoff, while calibrate models can provide more reliable estimates when given adequate site information. Full proceedings are available here.
Pete Kleinman – Modeling Phosphorus Runoff in the Chesapeake Bay Region to Test the Phosphorus Index
Modeling P runoff plays a fundamental role in the Chesapeake project. For each physiographic region, watersheds were identified where the SWAT model and the local P Index would be run to compare results. This objective has proven challenging to the SWAT model, as it requires a common scale of spatial inference with the P Index, i.e., the field. At the start of the project, the performance of SWAT was evaluated with regard to its representation of hydrologic and P cycling processes. It was determined that a version of SWAT that better represents variable source area hydrology, TOPO-SWAT, is best suited to the uplands of the Chesapeake Bay region. In addition, it was determined that the original P routines in SWAT are insensitive to the key nutrient management factors considered by the P Index (rate, timing, method and form of P application). Therefore, a new set of P routines was developed to correct the problem. Full proceedings are available here.
Deanna Osmond – Estimation of phosphorus loss from agricultural land in the Southern region of the USA using the APEX, TBET, and APLE models
Models predicted runoff accurately, but were unable to predict sediment or phosphorus losses accurately in many cases. Not surprisingly, models performed better when calibrated but even so predictions were problematic for particular locations and constituents (e.g. runoff in NC under no-tillage conditions and sediment at many sites). Full proceedings are available here.
John Lory – Estimation of phosphorus loss from agricultural land in the Heartland region using the APEX model: a first step to evaluating phosphorus indices
Full calibration provided excellent fit for runoff and total P (NSE>0.8 for each) and marginal fit for sediment (~0.3). In contrast, the BPJ resulted in unacceptable estimates of sediment and P load, and marginal fit for runoff volume (NSE~0.4). These results emphasize that failure to calibrate APEX with runoff and water quality data (the BPJ approach) will result in poor estimates of annual sediment and total P loads. Full proceedings are available here.
Reducing Loss
Josh Payne – Removing Phosphorus from Drainage Water: The Phosphorus Removal Structure
The P removal structure has removed approximately 67% of all dissolved P that has flowed into it over a 16-month time period. In addition, it has handled all flow volume from every event, including a runoff event that resulted in 600 gpm. That single event delivered 2/3 lb of dissolved P, in which the structure removed 66%. While the structure is removing P as predicted based on P loading, the structure has greatly outlasted the goal of removing 45% of cumulative dissolved P in one year. This is due to the below average rainfall received over the last two years. Full proceedings are available here.
Continuing Education Units
Certified Crop Advisers (CCA, CPAg, or CPSS)
View the archive and take the quiz. Visit the CCA continuing education page for additional CEU opportunities.