To investigate the effects of nitrogen reduction combined with biochar application on the growth of alfalfa and soil enzyme activities in the southern red soil, six treatments were established: CK, N100, N80, N80+BC, N60, and N60+BC. The plant height, leaf area, root activity, fresh grass production of alfalfa, and the activities of soil urease, acid phosphatase, and catalase were measured at different growth stages under each treatment. The results showed that the N80+BC treatment exhibited the best growth-promoting effects at all growth stages, with higher plant height, leaf area, root activity, and fresh forage yield than the other treatments. At the maturity stage, the above indicators under the N80+BC treatment were significantly increased by 25.12%, 42.77%, 194.11%, and 247.23% compared with CK, and by 26.87%, 31.53%, 41.57%, and 45.03% compared with N80, respectively. The activities of soil urease, acid phosphatase, and catalase under the N80+BC treatment were also the highest, which were significantly increased by 38.46%, 29.22%, and 59.90% compared with CK, and by 31.71%, 29.09%, and 33.20% compared with N80, respectively. In summary, nitrogen reduction combined with biochar application can promote the growth of alfalfa and increase soil enzyme activities in the red soil region of southern China, with the treatment of 20% nitrogen reduction combined with biochar showing the best effects.