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Following extensive land conversion from other crops to rubber plantations, Southeast Asia has become the main natural rubber producer in the world. Within Southeast Asia, Thailand is a leader of rubber production. This research addresses the question of the long-term effect of land conversion to rubber tree plantations on selected soil properties. The study reported here aimed to evaluate change in soil properties after 5 and 23 years of rubber tree plantation (5 RB, 23 RB) compared to soil properties under annual cash crops such as sugarcane (SG), in Kranuan district, Khon Kaen province, Thailand. Randomized sampling was conducted at soil depth increments from 0-10 to 150-160 cm. Topsoil organic carbon, total N and total K were higher in 23 RB than in the 5 RB and in the SG system. Available phosphorus in 23 RB was also higher than in soil under the 5 RB system, but not significantly different from that in the SG system. Soil pH was identical throughout the soil profile in the three observed cropping systems. We found evidence of soil compaction under the SG system at the 30-40 cm depth. Finally, topsoil in 23 RB had higher moisture content than that under the 5 RB and SG systems. Overall, this study indicated that, relative to cash crops such as sugar cane, conversion to rubber tree plantation in Northeast Thailand did not lead to land degradation and even improved some of the soil property indicators. [ABSTRACT FROM AUTHOR]