A series of kappa-carrageenan (kappa-CG) hydrogels were prepared by using glutaraldehyde (GA) as crosslinker for controlled releasing of copper and manganese micronutrients. The hydrogels were characterized by gel content, swelling and degradation tests, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Scanning Electron Microscope (SEM) observations. The variations of swelling percentages (S%) with time, temperature and pH were determined for all hydrogels. As the amounts of crosslinker increased, S% decreased regularly in contrast to gel content results. The higher swelling values were obtained in basic medium than acidic and neutral mediums for all kappa-CG hydrogels. Releasing of copper and manganese micronutrients from kappa-CG hydrogels was investigated in water and soil. A simulated releasing model was also applied to estimate the releasing behaviors in agricultural irrigations. In all release studies, the cumulative release values increased with decreasing GA amounts. The release kinetic parameters were also calculated. It was detected that the releasing of micronutrients in soil was slower than that in water.