The traditional understanding of how plants take up and use nitrogen has been that plants can only use the mineralized forms of N. For example, The University of California’s Publication 7249, Soil Fertility Management for Organic Crops, states “organic nitrogen must be mineralized through the action of soil microbes before it is available to available for plant uptake.” And the IPNI’s ENVIRO-BRIEF No. 1 claims “All the nutrients contained in any organic source remain unavailable for crop use until the material is decomposed (mineralized), releasing its nutrients to the inorganic soil pool.” Similar comments are found throughout literature on crop nutrition. So, it is not surprising that research on organic fertilizers has focused on the conversion of the organic matter and proteins to the mineralized forms of nitrogen, as seen in this chart from Publication 7249.
Much needs to be done to better understand how organic forms of nitrogen behave in different soil conditions and how they affect plant growth. But, rather than waiting for the science to supply all the answers, organic and sustainable farms can benefit from the practical experience gained.