Testing Wisconsin P index assessments across cropping systems.

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• Managing agricultural runoff phosphorus (P) is crucial for environmental sustainability.
• Understanding the differences between dissolved P (DP) and particulate P (PP) is essential for effective management.
• The Wisconsin P index (WPI) is a tool used to assess land management effects on P runoff.

Purpose of the Study:

• To test the WPI's ability to identify P loss tradeoffs between tilled corn silage and perennial forage cropping systems.
• To evaluate the WPI's sensitivity to treatment differences within cropping systems.
• To validate WPI estimates using monitoring data.

Main Methods:

• Utilized monitoring data to compare WPI estimates with actual P losses.
• Analyzed P losses in terms of dissolved P (DP) and particulate P (PP).
• Incorporated measured suspended sediment, precipitation, and runoff data into the WPI model.

Main Results:

• WPI estimates were generally supported by monitoring results.
• Corn systems showed higher total P losses dominated by PP, while perennial forage systems had smaller losses dominated by DP.
• The WPI accurately distinguished most treatment differences within systems, but underestimated winter runoff and showed specific over/underestimations for DP and sediment P.

Conclusions:

• The WPI is a valuable tool for assessing P runoff and guiding nutrient management.
• The model shows potential for adaptation to other cold climate regions.
• Specific areas for WPI improvement include winter runoff and differentiating P forms in various cropping systems.