The Phosphorus Index (PI) estimates the relative risk of P loss from agricultural fields and encourages the implementation of best management practices to reduce this risk. A majority of states designed their own PI version to address local conditions and priorities, resulting in a large variation in PI structures among states. Currently, multiple projects nationwide are evaluating if the different PIs are directionally and magnitudinally correct in ranking fields based in their potential for P loss. In the Chesapeake Bay, New York (NY), Pennsylvania (PA), Delaware (DE), Maryland (MD), Virginia (VA), and West Virginia (WV) are working cooperatively to fulfill this objective. Several approaches have been proposed to determine the effectiveness of the various PIs. The following results summarize one approach: a survey of certified nutrient management (CNMP) planners with questions specifically related to their perspectives on the NY and PA PIs. This approach recognizes that planners have experience with the PI and have a close knowledge of the landscape scenarios and management that have previously resulted in water quality violations.
A total of 36 CNMP planners were surveyed in NY in the winter of 2013-2014. The survey included questions about (1) the relative importance of the different factors in the current PI; (2) the main reasons for water-quality violations; (3) the management practices the PI should encourage and discourage, (4) the use of a screening tool to identify fields that need and do not need a PI assessment; and (5) the PI assessment across and within geographic regions.
In PA, a survey structure and question content similar to NY was used to ensure comparability of results. Certified private and public nutrient management (NM) specialists as well as other members of the PA NM community received the survey in the spring of 2014.
All source and transport factors included in the NY PI were considered important by the CNMP planners. More than half of the planners indicated that the water quality violations were mainly driven by manure applications (1) just before snow melt or rainfall events, (2) on frozen or saturated soils, (3) too close to streams or ditches, or (4) without incorporation. Many nutrient management planners suggested that the PI should incentivize manure incorporation, implementation of cover crops, setbacks and buffers, and preferential manure applications to fields without connectivity. A high percentage of planners also suggested that the PI should discourage manure applications to saturated or frozen soils, to fields close to streams, to fields with steep slopes, manure spreading without incorporation, and high manure rates. Several CNMP planners in NY indicated the weighting of factors in the NY PI should be reevaluated, in particular, the timing of manure application. Some planners proposed to use real weather data to fine-tune the timing of manure application, while others suggested replacing the calendar year as a driver for PI weights by field conditions. Most of the CNMP planners in NY (1) did not support including a screening tool to quickly identify fields of no P runoff risk in the revised PI,(2) supported a physiographic-based PI (NY plus Northern PA), and (3) did not support multiple PIs within the NY. Some planners also raised concerns about the lack of systematic assessment of water quality, and the attempt to numerically predict P loss as opposed to predict the relative risk of P applications.
Overall, responding NM specialists indicated a need to revise the PA PI and favored the continued use of a screening tool. State boundary was the preferred regional basis for revising and implementing the PA PI, but some respondents showed support for using physiographic region. Current, PA PI source and transport factors were considered important and reliable in assessing fields for vulnerability to P loss. However, many NM Specialists recognized other potential PA PI factors such as flooding frequency, concentrated flow, leaching potential, and degree of soil P saturation as important for consideration in revising the PA PI. Based on their experience, respondents reported water quality violations typically resulted from manure spills, manure discharge events, and erosions events. Management practices to be encouraged by the PA PI include buffers, cover crops, and erosion control practices such as no tillage. In turn, management practices to be discouraged by the PA PI include winter manure application and manure application to land without suitable cover.
The management practices identified by CNMP planners will be evaluated in the revised version of the NY PI.
The information obtained from the PA survey will be considered in the PA PI revision process. Similarities in responses between PA and NY especially with respect to practices to be encouraged or discouraged by the PI demonstrate the need for continued cooperative regional work and PI evaluation.
Quirine M. Ketterings, Professor, Cornell University firstname.lastname@example.org
Sebastian Cela, Postdoctoral Associate Cornell Univ.,Karl J. Czymmek, Senior Extension Associate Cornell Univ., Jennifer Weld, Graduate Student Penn State, Douglas Beegle, Distinguished Professor Penn State, Peter Kleinman, Research Leader USDA-ARS PSWMRU
For additional information, contact Quirine M. Kettertings at email@example.com
This project is funded by a USDA-NRCS CIG Grant.
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