At what temperature does ESN begin to release? Does ESN release N below 50 degrees F?

The release of N from ESN is temperature dependent, but there is not a specific “on-off” temperature.  Practically, ESN can start releasing N at temperatures above the freezing temperature of water, since liquid water is necessary for the diffusion process, but ESN releases very slowly at cold temperatures to protect the N when crops are growing slowly.  ESN release does not start at 50 degrees F, but the release is very slow at lower temperatures and increases gradually as temperature increases to better match crop N demand.   

See figure/fact sheet illustrating ESN release at different temperatures for more information.