Poly(acrylic acid) (PAA)-based controlled release fertilizers with ammonium nitrate or carbamide were prepared using microwave irradiation. The obtained hydrogels were characterized by swelling behavior and ammonium ion release. It has been found that at higher amounts of crosslinker (N,N`-methylenebisacrylamide), the hydrogel network chains became less flexible. It causes a decrease in the swelling ratio of the hydrogel. The swelling of hydrogels containing ammonium nitrate decreased with increased concentrations of ammonium nitrate. The reason is the presence of ionic groups during agrochemicals’ release in water. These ions prevent water molecules from diffusion into the hydrogels, thus decreasing the swelling capacity of the hydrogels. The release rate is the highest during the first 24 hours, then reaches a plateau.