The purpose of this research is to construct an operational computer model to represent the on-farm production system of the chanasutr land consolidation project, location within the upper Chao Phraya Basin Irrigation Scheme. Agricultural development policies are to be applied to the model which serves as a development planning laboratory, to learn how they govern the behavior of the system. Simulation technique enables the tracing of the system behavior step-by-step through time and the comprehensive comparisons of alternative policies. The methodology used is called System Dynamics. The model, expressed in Dynamo language, comprises 13 subseptems. Policies on land consolidation repayment rate, population, cropping pattern, off-farm income, short-term loan and farm-input price subsidy, etc. are used for analysis. More than one hundred output variables pertaining to employment, irrigation, farm machinery, budget, debts, etc., are presented in tables and time-series plots (20 years). Some of the significantfindings : creation of off-farm income proved to be one of the most effective policies. Aids in term of short-term loan and farm-input price subsidy may aggravate farm indebtedness. Revenue from a full-scale wet-season rice production and dry-season rice production in only 30 percent of the area, plus an annual off-farm income of less than 10,000 bahts, is barely enough for family expenditure and the repayment of the heavily subsidized land consolidation project. And under this condition, the land-holding size per family should not be less than 20 rais (3.2 hectares). Sugarcane is proved to be a good substitute crop when water is limited because of its higher income per unit of water consumption.
