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April, 2000
SITE-SPECIFIC MANAGEMENT GUIDELINES
SSMG-13
Identifying Good Candidates for Precision Phosphorus Management - D.E.
Clay, D.D. Malo, C.L. Reese, and C.G. Carlson
1. Findings from this study are applicable to fields with phosphorus (P)
frequency distributions similar to that shown in Figure 1. In fields with high
soil test P variability, precision management of P produced the greatest level
of profitability when the composite soil test P level was in the high to very
high soil test P categories.
Average soil P test level and prior field histories can be used as a decision aid to reduce economic risks associated with adopting precision farming techniques.
Appropriate P response models and yield goals must be used to accurately assess potential profitability associated with precision P management.
SSMG-1
Site-Specific Use of the Environmental Phosphorus Index Concept
Phosphorus (P) loss to surface water can have negative impacts on the
environment. The risk of such loss depends on both source (added fertilizer and
manure, soil P) and transport factors (erosion and surface runoff). Fields at
risk are those where areas of high P application or soil P coincide with zones
of active surface runoff or erosion. A P index has been developed to rank field
vulnerability to P loss so that high risk fields may be identified for
site-specific management. The index provides a framework that can be regionally
adapted to prevailing topography, geology, and climatic conditions and requires
only readily available data. This fact sheet describes the technical basis of
the index and shows its application to a watershed in Pennsylvania.
Roger Brook
