This paper describes one of three operational state computer systems used to give advice on agricultural problems in the GDR. The system, employed nationwide, is oriented to providing advice about fertilizer application on farms or even single fields. Of the other two computer systems, one is described in IIASA CP-79-18, "Environmental Problems of Agriculture II: Pest and Weed Management: Monitoring and Forecasting in the German Democratic Republic." The remaining operational system is applied to irrigation. 

At IIASA's request, the present paper emphasizes the methods of the system for determining the optimal amount of fertilizer to apply which allows for maximum agricultural production without wasting resources or harming the environment. The paper thus offers another contribution to the solution of nonpoint source chemical pollution problems which have been intensively studied at IIASA both in-house and in cooperation with other institutions.