Development and Adaptation of Phosphorus Nutrition Indices for Different Major Crop Species in Organic Farming

In organic farming (OF), soil analysis is not always well adapted to correctly identify situations with phosphorus (P) deficiency risk for crops. The phosphorus nutrition indice (PNI), which relies on plant analysis, could be a complementary indicator for this diagnosis, but due to the lack of references ready to use for interpreting PNIs, especially for legumes, it remains rarely used in field crops. The first part of the study focused on establishing critical P content equations for soybeans and alfalfa. The second part defined threshold values for these two crops and as well for bread wheat and maize, above which yield is not negatively impacted. Finally, the references obtained were tested on a field observatory in OF. While the diagnosis results obtained using PNI on wheat and maize appear promising, validation in a broader range of situations is still needed for both legumes.