Cu polyaspartate was pptd. from aq. solns. of K and NH4 polyaspartates and used as an additive to a corn. mineral fertilizer to study its effect on release of nutrients to the soil under lab. conditions. The addn. of Cu polyaspartate resulted in a controlled slow release of Cu and N elements to the soil. The Cu polyaspartate produced by conversion of NH4 polyaspartate was more efficient than that produced by conversion of K polyaspartate.