There are many applications, in particular to cryptography. There is a book Applied Algebraic Dynamics;
see also the articles T-functions revisited: new criteria for bijectivity/transitivity and Secure cloud computations: Description of (fully)homomorphic ciphers within the P-adic model of encryption.
Biology: Automaton model of protein: Dynamics of conformational and functional states
Cognition and psychology:
A.Yu. Khrennikov, Human subconscious as the $p$-adic dynamical system. Journal of Theoretical Biology, 193, 179-196 (1998).
D. Dubischar, M. Gundlach, O. Steinkamp, A.Yu. Khrennikov,
A $p$-adic model for the process of thinking disturbed by physiological and information noise. Journal of
Theoretical Biology, 197, 451-467 (1999).
A.Yu. Khrennikov, Information Dynamics in Cognitive, Psychological, Social and Anomalous
Phenomena, Springer-Science + Business Media, B.Y., Dordrecht, NL, 2004.
Albeverio S, Khrennikov A and Kloeden P E Memory retrieval as a $p$-adic dynamical system
BioSystems 49 105--115 (1999).
Khrennikov, A. (2002). Classical and Quantum Mental Models and Freud's Theory of Unconscious Mind.
Växjö, SWE: Växjö University Press.
A.Yu. Khrennikov, Modelling of psychological behavior on the basis of ultrametric mental space:
Encoding of categories by balls. P-Adic Numbers, Ultrametric Analysis, and Applications, 2, 1-20 (2010).