Abstract: Few studies have been concerned in physiological effects of REEs on forages, and the mechanism of action by rare earth elements (REEs) is still not clear. The studies on the action of REEs soil application to crop are still rare. A pot experiment was conducted to study the effects of spray application and soil application of lanthanum (La) on growth of leguminous grass Chamaecrista rotundifolia in order to provide theoretical reference for reasonable applications of REEs in agriculture. The results showed that both methods obviously increased the chlorophyll content of leaf, leaf area and dry matter weight of C. rotundifolia. At each sampling date, the shoot dry matter weight of Y2 treatment was the highest for spray application, with 15.91–20.03% (P<0.05) higher than the control. The shoot dry matter weight of Y8 treatment was the highest for soil application, with 14.28–17.42% (P<0.05) higher than the control. At each sampling date, the root dry matter weight of Y2 treatment was the highest for spray application, with 19.88–25.34% (P<0.05) higher than the control. The root dry matter weight of Y8 treatment was the highest for soil application, with 21.41–27.03% (P<0.05) higher than the control. At the same La application rate, the dry matter accumulation showed no significant difference between spray application and soil application. Furthermore, the highest dry matter accumulation also showed no significant difference between Y2 and Y8 treatments. Judging from this, spray application was more effective with lower application rate, lower cost and more environmental protection than soil application. The reasonable La ap-plication rate for soil application REEs was 1–2 times of that for spray application. The concentration of La in each part of C. rotundifolia plant increased with the increase of La application rate. The concentration of La in soil changed little, because the background concentration was high, the application rate was very low and the uptake rate by C. rotundifolia was low.