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Updated
06/25/2007 |
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Introduction
to the Postions Papers
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Phosphorus
Management Within Multi-State Watersheds - Management
of phosphorus (P) on agricultural fields must be based on nutrient management
planning,
which
requires
soil testing
for commercial fertilizer or P-Indices for animal waste recommendations.
Generally, soil testing and P-Indices produce state-specific recommendations.
For farmers working across state boundaries, differences in soil test
interpretations and resulting recommendations for commercial P fertilizer
or animal waste application rates can be confusing. It is the intent
of this paper to explore the basis behind some of the recommendation
and policy differences that arise across state boundaries in making
P management recommendations. Lead Member: Deanna Osmond
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Soil
Sampling Methods for Phosphorus - Spatial Concerns - Knowledge
of soil phosphorus (P) levels is an essential component of nutrient
management
planning
for crop production and for tools that assess the risk of P loss from
agricultural fields. Historically, soil P testing has been used to estimate
P availability for crops and is now being used directly or as a component
of P indices to assess the risk of P loss from fields to water resources.
A basic assumption of soil testing for crop production is that the soil
sample collected represents a certain area with an acceptable margin
of error. Therefore, appropriate soil sampling methods are needed for
effective agronomic P management and environmental P assessment.
This position paper summarizes important practical aspects of topsoil
P variability (within 20 cm depth) across the landscape with
an emphasis on within-field variability, and sampling methods that have
been recommended or proposed to assess soil P and suggests practical
soil sampling options for agronomic and environmental purposes. Lead
Member: Antonio Mallarino
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Predicting
Edge of Field P Losses -
One of the major issues raised in recent lawsuits was the need
for predictive models that accurately predict edge of field P loss
predictions. Specific
questions posed include i) what is the capability of and time
frame for developing
models, ii) what type of model should be used (e.g., qualitative
vs. quantitative models, and iii) how accurately do existing models
predict P loss?
Lead Member: David Radcliffe
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Soil Phosphorus
Threshold Levels
- The P Site Index concept was developed in part as a more comprehensive tool
than the single factor approach of using the soil test phosphorus (STP) thresholds
to assess the potential for edge of field P loss and decide whether a field
could receive manure. While the STP concentration in the soil is important,
a large body of research shows that other field and management factors (i.e.,
source and transport) are equally, if not more, important. Thus, the
STP Threshold approach was abandoned as the sole source of P-based management
guidelines in lieu of a more comprehensive P Index. Some questions raised
in recent lawsuits include can a "defensible" STP threshold be developed
and what are the scientific limitations of this approach? Lead
Member:
Sam Feagley
(In progress)
Comparing
Methods of P Analysis – Analytical
methods for estimating P availability in soils and manures need to be
kept current by incorporating results from recently published research.
For example, differences exist in measured P levels in manure and soil extracts
depending on whether P is determined using the older colorimetric
methods or by Inductively Coupled Plasma spectroscopy (ICP). These
differences can significantly affect the accuracy of tools or models to
predict
edge of field P loss. As noted from the Eucha-Spavinaw case, policy makers
and the court find this hard to accept and understand. This paper
summarizes the differences anticipated between
P analytical methods, and give recommendations
regarding use. Lead
Member: Gary Pierzynski
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Soil
Sampling Depth for P Assessment – Soil
testing for P will remain an inherent part of the nutrient management planning
process for both agronomic and environmental purposes.
For environmental
soil P testing, general recommendations of sampling depth for pastures, conventional
and reduced tillage systems are described. Lead
Member: Peter Vadas
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The Phosphorus
Site Index as a P Loss Assessment Tool
– Many of our policy makers and the general public do not have a good
understanding of the concept or the potential use of the Phosphorus Index
as a tool in agricultural P management.
This paper describes the concepts and science behind the P-Index, as well
as the benefits and limitations of
its use. Lead
Member: Rory Maguire
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