Phosphorus Indices: an Understanding of Upper Mississippi Strategies John A. Lory, Ph.D. Division of Plant Sciences University of Missouri

Outline Overview  Phosphorus indexes: why do we need them?  Does it make sense that every state is different? Missouri P index  Our objectives.  What you need to make it work.

Many streams and lakes are phosphorus limited. Jones and Knowlton 1993 Water Clarity as measured by Secchi depth (m) Missouri reservoirs

Challenge: Where, when, and how to apply manure to minimize P loss to surface water.

Runoff volume Method of application Time since application Application rate Soil test P Soil type Cultivation Vegetative cover Factors affecting runoff of P

Nutrient planners are required to assess phosphorus loss on all fields receiving manure.

You choose the method Agronomic soil test recommendation  Objective: does the crop need P? Phosphorus threshold Phosphorus Index  Objective: will applied P be vulnerable to losses?

Low N-based Applications Medium N-based Applications High P-based Applications Very High No Manure Applications Phosphorus Assessment

Assessment tools are state specific. Index Target: - Runoff - Irrigation - Runoff - Irrigation Long-term Runoff - Runoff - Leaching

Assessment tools are state specific. Approach: Multiplicative tabular factors Simplified model Additive tabular factors Simplified model

Do Differences Between States Make Sense?

Missouri’s approach: 2 choices Agronomic soil test recommendation  Objective: does the crop need P? Phosphorus threshold Phosphorus Index  Objective: will applied P be vulnerable to losses?

Missouri P index objectives Strategic planning tool for use in writing a 5-year nutrient management plan. Identify fields where field characteristics are likely to result in high P loss in runoff. Simple to use with readily available information for people with an NRCS conservation plan.

6 Factors in the Missouri P index Soil test result  include units and sampling depth Tillage  Tilled vs. notill and forages RUSLE estimate of erosion Land cover Soil hydrologic group  A, B, C or D Distance from water feature

Simple model approach Sediment P  Function of RUSLE-2 erosion, soil test P and sediment delivery ratio. Soluble P  Function of runoff volume (curve number approach and soil test P).

Higher standard in the clear-water region of the state.

P index rating system RatingClear-water region Other Low<1 <3 Medium>1 and 3 and <7 High>5 and 7 and <12 Very High>10 >12

6 Factors in the Missouri P index Soil test result  include units and sampling depth Tillage  Tilled vs. notill and forages RUSLE estimate of erosion Land cover Soil hydrologic group  A, B, C or D Distance from water feature

Surface applications require a tactical tool. Educational tools being developed to identify times of year runoff least likely Inputs:  Ground cover- County  Soil hydrologic group- Soil condition  Soil moisture Output  Evaluation of runoff risk (low, medium, high)  Predicted rainfall amount needed to initiate runoff

P index developed cooperatively by MU and NRCS. Based on best professional judgment. Available as a spreadsheet at:

Future P index integrated into RUSLE 2 notification system to help evaluate timing of manure applications.