The purposes of this study are to construct a system dynamics model on the behaviors of rice trade pertaining to farmers of Ongkharak District, Nakornnayok Province when the paddy drying silo is available and to study the effects of paddy drying silo on farmer’s rice paddy trade. The collection of information for this study derived from 2 sources consisted of 1) Primary Information : Interviews with 21 farmers and 20 concerned persons of Village No.12 1 Sisakrabue Sub-District, Ongkharak District, Nakornnayok Province, 2) Secondary Information : statistical information database collected by concerned public offices. The collection of information from said two sources was analyzed in findinging for factors affecting the system behaviors, structural correlation, and used for a construction of a dynamics system simulation by Powersim Construction Version 2.51 Software, which analyzed the system behaviors using correlation graphs to explain the behaviors of farmer rice trading when paddy drying silo is available during the period from March 1999 to February 2001. This study found that the construction of dynamics system model constructed was capable of explaining the behaviors of farmer rice trading, capable of giving a net estimated income on the sale of the rice paddy when the paddy drying silo service is provided. For an instance farmers using the paddy drying silo service with hold on or storage period of not excessive to 18 weeks and 4 weeks were with net income revenue more than farmers who sold their rice paddy immediately right after the harvest, by which the farmers were with increased average net income revenue of not exceeding Baht 226.39 and 45.91 per ton respectively. And it’s found that when the service free of paddy dryer is about Baht 200 per ton 1 the quantity of paddy undergoing the paddy drying silo ranged from 5.4355 - 9.0068 per tons per week. Through the analysis of the system dynamics model by adjusting the service fee on the paddy dryer and the price of 15% paddy. It was found that the service fee of paddy dryer service should not exceed Baht 80 per ton, which was the rate which can generate a sufficiently net income revenue to persuade farmers to use paddy drying silo service. And farmers who can hold on to the paddy for the best sale for maximum of 4 weeks should use the service of paddy drying silo until the price of 15% paddy increases at least 3% minimum. And farmers who can hold on to the paddy for the best sale for maximum of 18 weeks should use the service of paddy drying silo until the price of 15% paddy increases at least 1.5% minimum.
