Relationships between soil test phosphorus and county-level agricultural surplus phosphorus

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• National nutrient inventories estimate surplus phosphorus (P) using county-scale mass balance.
• Few studies link these inventory-based surplus P estimates to measured soil test phosphorus (STP) concentrations from large-scale soil testing programs.

Purpose of the Study:

• To assess the relationship between national surplus P data and laboratory-measured STP at the county scale.
• To determine optimal aggregation periods for surplus P data to correlate with STP.
• To compare the correlation of surplus P with individual P inventory components (fertilizer, manure, crop removal).

Main Methods:

• Utilized the NuGIS dataset for national surplus P data.
• Analyzed laboratory-measured STP data at the county scale for Arkansas, North Carolina, and Oklahoma.
• Employed Pearson and Spearman correlation coefficients to assess relationships between surplus P and STP.

Main Results:

• Surplus P was positively correlated with STP across all studied states (Arkansas, North Carolina, Oklahoma).
• Optimal surplus P aggregation periods varied by state (10 years for AR, 30 for NC, 4 for OK).
• STP generally correlated better with surplus P than with individual P inputs/outputs, except in North Carolina.

Conclusions:

• Surplus P moderately correlates with measured soil test phosphorus (STP) concentrations.
• The strength of the surplus P-STP relationship is influenced by the data aggregation period and location-specific factors.
• Findings highlight the utility of surplus P estimates but emphasize the need for careful consideration of temporal and spatial scales.