Solid polymeric matrices based on xanthan and chitosan and using KNO3 as a model agrochemical were prepared by direct compression, with a view to evaluating their potential as controlled-release fertilizers (CRFs). The swelling behavior, surface characteristics, and durability in soil of the tablets were studied. The release data were treated with a power law model in order to understand the delivery kinetics of KNO3. This proved to be non-Fickian diffusion, with release exponents ranging from 0.80 to 0.88, highlighting the importance of polymer relaxation on drug release. The presence of drug-free surface layers was an important factor in modulating the release. When comparing experiments without and with stirring, the release time ratios between them were as high as 40, predicting a significantly greater release time in soils. In durability experiments in soil, the polymeric matrices lasted longer than 6 weeks. These results show that layered xanthan and xanthan-chitosan matrices perform as a promising system for developing CRFs. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2422-2428, 2013