The IPNI Nutrient Removal Calculator (NRC) provides estimates of crop nutrient removal for a selection of important world crops.
© International Plant Nutrition Institute 2013
Settings/User Preferences
Units – NRC calculates nutrient removal in both metric and imperial/US units. Users select their initial preference when starting up the NRC. This setting can be changed within the user preference setting 
Languages – NRC is a multilingual publication available in English, French, Spanish, Portuguese, Russian, and Mandarin (Chinese). Your language is automatically detected. This setting can be changed within the user preference setting
Crop favorites – For quick access, NRC allows the creation of a short list of common crops of interest. Add or remove crops to your favorites list by selecting 
Nutrient Removal Calculation
NRC provides estimates of crop nutrient removal for nitrogen (N), phosphorus (P) expressed as P2O5, potassium (K) expressed as K2O, and sulfur (S).
Table of Unit Conversions
http://www.etoolsage.com/converter/agriculture.asp
Current Data Sources
Please see: http://info.ipni.net/NRCDATA