The effects of organic nitrogen in place of chemical nitrogen on maize root characteristics in the karst peak-cluster depression and the relationship between their root traits and yield under the same nitrogen input level were investigated. A field experiment included six treatments, no fertilizer(CK), chemical fertilizer only(NPK), 70% NPK+30% straw(J1), 70% NPK+30% cattle manure(N1), 40% NPK+60% straw(J2), and 40% NPK+60% cattle manure(N2) were performed. The maize fine root morphology at different soil depths(0-14, >14-28, >28-42 cm) were analyzed by means of minirhizotrons. The results showed that no statistically significant differences in maize fine root characteristic indicators were observed among treatments in the 0-14 cm soil layer. In the >14-28 cm and >28-42 cm soil layers, all fine root characteristic indicators of the J1 treatment, except fine root diameter(RD), were the highest and significantly greater than those of CK. In the >14-28 cm soil layer, the fine root total root length(RL) of J1 was 409.32 cm, significantly higher than those of N1 and N2, and the fine root surface area(RSA) and fine root biomass(FRB) of J1 were 54.13 cm2 and 1.25 cm/cm3, respectively, both significantly higher than those of N1. In the >28-42 cm soil layer, the RSA and fine root volume(RV) of J1 were 66.05 cm2 and 0.88 cm3, respectively, significantly higher than those of N1. Only the CK treatment exhibited significantly lower RL, RSA, number of fine root tips(Ntips), and FRB in the deepest soil layer compared with the upper two layers, while no statistically significant differences in fine root characteristic indicators among soil layers were detected for the other treatments. No statistically significant differences in yield indicators were found among the fertilization treatments; however, aboveground dry weight per unit area(ADW) and production output per unit area(PO) were significantly higher than those of CK. The correlation between yield indicators and fine root characteristic indicators strengthened with increasing soil depth. Plant height(PH) and ADW were significantly negatively correlated with RD in the 0-14 cm soil layer. ADW was significantly positively correlated with RL, RSA, FRB, and RSA density in the >14-28 cm soil layer. In the >28-42 cm soil layer, ADW was highly significantly negatively correlated with RD, and significantly or highly significantly positively correlated with the other fine root characteristic indicators. In conclusion, the fertilization treatment J1 with 70% NPK and 30% straw significantly promoted maize root growth. This indicates that partially substituting chemical nitrogen fertilizers with straw in karst peak cluster depression areas is conducive to fostering deep root systems.