The present agriculturists in Thailand are still facing the problem of gaining less profit from growing rubber trees. The main reason is that it takes a very long time for the rubber trees to grow until they can produce rubber latex. For this reason, some agriculturists have less income while waiting for the rubber trees' growth. So, some agriculturists decide to grow other useful plants to increase revenue, such as cassava, corn, etc. From the study of agricultural potentiality, in Somdet district, Kalasin province, using 20 percent of the population randomly, agriculturists can increase additional revenue by growing some additional plants in the rubber tree plantation fields when the rubber trees are 1-4 years old. The most important additional plants in Kalasin Province cover an area of the 280,530 rai, representing 12.29% of the total cultivated area. The average income of 11,537.5 baht per year is for agriculturists who don’t have an additional occupation. Moreover, agriculturists have additional revenue, at the very beginning of the planting season when the rubber trees are 1-4 years old, from raising cattle, with an average income of 10,5990.16 baht per year, higher than those who have no extra occupation by 24.9 percent.