This paper deals with the analysis of the impact of credit rationing on the farmer’s economic equilibrium and the analysis of different policy scenarios in a derived neoclassical adjustment cost framework. The theoretical model is an optimal dynamic investment model, in which the upper bound on investment is introduced. The limit of the investment enables to analyse the consequence of the occurrence of credit rationing on farmer’s capital accumulation, investment and supply. The method of optimal control is used to solve the optimization problem. The results show that the occurrence of credit rationing may significantly determine a farmer’s economic equilibrium. Then the analysis of defined policy scenarios suggests that a loan guarantee efficiently solves the problem of the occurrence of external credit rationing. Interest rate subsidy may produce overinvestment and, thus, increases the probability of occurrence of the crowding-out effect, especially in the group of non-credit constraint farmers. Moreover, as far as the cost of agricultural policy is concerned, other agricultural support tools are less effective. The numerical application shows that the farmer’s economic equilibrium is mostly sensitive to the initial bound on investment, the parameter of the cost function, the price, the level of technology and the discount rate. Finally, if the uncertainty is introduced, then the level of investment spending and capital accumulation is lower.