December 09, 2014 / by John

Mapping Field-level Soil Phosphorus on the Eastern Shore

Working with Center for Progressive Reform (CPR) and Environmental Integrity Project (EIP), our team completed the mapping of soil phosphorus test results for over 1,000 fields belonging to 60 confined animal feeding operations on Maryland’s eastern shore. Data were obtained from public comprehensive nutrient management plans (CNMP) resulting from a public information act request made by CPR and then geo referenced by hand using the CNMP paper maps.

To help farmers make decisions about manure application, the CNMPs include “fertility index values” (FIVs). This index aids farmers in determining whether adding additional phosphorus will help crops grow. Maryland interprets FIV scores in four categories: low is 0-25; medium is 26-50; optimum is 51-100; and excessive is 100 and higher. Low and medium FIVs tell farmers that crops would grow better if additional phosphorus is applied. Optimum FIV levels, tell the farmer that existing soil phosphorus is sufficient for plant growth. Excessive FIVs tell farmers that there is already more than enough phosphorus in the soil to meet the needs of most crops and that it is unlikely that crops will respond positively.

FIV Range FIV Class Anticipated Crop Response
0 - 25 Low Yield response is likely if fertilizer is applied
26 - 50 Medium Yield response possible if crop is fertilized
51 - 100 Optimum Yield response unlikely if additional fertilizer is applied to crop
Above 100 Excessive Yield response very unlikely


The map shows the soil phosphorus FIV values from the fields that were tested when a CAFO prepared its CNMP. While the tests were conducted from 2008 to 2014, the results remain relevant as they were used to plan the fields’ fertilization needs over the next five years and were provided in response to CPR’s request for the most recent CNMP on file. The fields marked with yellow dots have P FIV values under 150 and would not be subject to the new regulations. All the other fields, marked in oranges and reds, would likely be subject to the PMT, depending upon the average P FIV value of the entire farm, calculated by excluding all fields below 150 and averaging the P FIV values greater than 150. Based on the farm’s average field P FIV value the operation is placed in a low, medium, or high priority bracket for PMT phase-in. (the proposed regulations define how to calculate average P FIV).

If you have general questions or comments on how this map was created, ping me on twitter, @JohnDawes4. Full reports of EIP and CPR’s analysis can be found below:

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