Objective The aims was to understand the effects of Eucalyptus urophylla and Acacia crassicarpa plantations on soil cation exchange capacity (CEC) and its impact factors in Heshan, Guangdong Province.

Methods The soil CEC and ecological stoichiometric characteristics in E.urophylla and A. crassicarpa plantations after 15-year afforestation were determined in Gonghe Town of Heshan, and the characteristics and correlation of soil CEC and other indices of two plantations were analyzed, and the key factors affecting the soil CEC in afforestation of two plantations were comprehensively evaluated by principal component analysis (PCA) method.

Results The results showed that the total amounts of CEC, total exchangeable base (TEB), base saturation (BS) in the soil of A.crassicarpa plantation were significantly higher than those of E. urophylla plantation. The content of exchangeable Ca^{2 +} of A. crassicarpa was significantly higher than that of E. urophylla, but the contents of exchangeable K ⁺ , Na ⁺ and Mg^{2 +} were not significantly different between the two stands. The ratios of Ca^{2 +} /Mg^{2 +} , Ca^{2 +} /Mg^{2 +} , Ca^{2 +} /K ⁺ and (Ca^{2 +} + Mg^{2 +} )/K ⁺ were found to be significantly higher in A. crassicarpa than those in E. urophylla. Correlation analysis showed that soil CEC was positively correlated with SWC, TOC and TN in E. urophylla plantations. Soil CEC was positively correlated with TN and C/N, and was positively correlated with C/P and C/N/P in A. crassicarpa plantation. The PCA showed that soil TEB, TP, Na ⁺ , BS, Ca^{2 +} , Mg^{2 +} and soil pH were the key factors affecting soil CEC in this region.

Conclusion In Gonghe sample site of Heshan, A. crassicarpa plantation significantly increased soil CEC, TEB and BS compared to E. urophylla plantation, suggesting that A.crassicarpa plantation has more advantages in maintaining soil fertility.