A detailed description of the methods utilized to produce the data, as well as research results, are described in Philip Potter and Navin Ramankutty, et. al. (2010) (journal article, download PDF). Areas of fertilizer application and manure production were identified and mapped using two different multi-stage processes. Where necessary, data were standardized to ensure consistent global coverage.
Fertilizer Application rates were computed by fusing national level fertilizer data and global maps of 175 crops. Data on fertilizer application rates for two major fertilizers, nitrogen and phosphorus, for 88 countries were utilized from "Fertilizer Use by Crop, 2002", a report for the International Fertilizer Industry Association (IFA). These data accounted for over 90% of global fertilizer consumption. Years for which the data were reported range from 1994 to 2001. Additional data on fertilizer application were gathered from the Food and Agriculture Organization of the United Nations (FAO) and the International Fertilizer Development Center (IFDC) to encompass the 161 countries considered in the analysis. Crop data for global mapping were gathered from the "M3-crop" database. To maintain consistency, the multi-stage process included scaling fertilizer application rates based on the ratio between the areas reported in the IFA database with the area calculated using the M3-crop data. This method calculates the total amount of nutrients in the fertilizer applied directly to the land.
Manure Production rates are based on livestock head count and nutrient content of manure. Standardized global data of livestock distribution were gathered from the FAO Gridded Livestock of the World (GLW) project. Additional data were gathered regarding the nutrient content, specifically nitrogen, phosphorus, and excrement rate for various livestock from each Organization for Economic Co-operation and Development (OECD) country. Different livestock datasets were converted into equable "livestock units" depending on the inputs necessary for livestock in each region, then excrement nutrient content of the manure was calculated uniformly across the globe. The data values represent the amount of nutrients produced, not the recoverable fraction or the amount collected and returned to the fields.
SEDAC thanks Drs. Potter, Ramankutty, Bennett, and Donner for providing these data for distribution.