The expansion of the agricultural border in brazilian savannahas with the farming production in wide scale extends the environmental costs, however it depends essentially on the adopted technique of plantation. The study it evaluates economically, by Replacement Cost Method, the environmental impacts of technologies of soy and corn plantation. In the case of the soy the no tillage raises the cost of production in 0,47%, but it provokes a reduction of (- 81,22%) in the environmental cost. In the corn, the costs of no tillage are (- 5,92%) lesser of that conventional tillage and provoke a reduction in the environmental cost in (- 29,43%). In the specific region of the study the annual ambient damages caused by the conventional tillage had been esteem in R$ 317,213.39 and the no tillage of R$ 81.375,76. The adoption of the no tillage in the plantation of soy and corn demonstrates its bigger social effectiveness for the reduction of the erosive process and improvement of the outflow and the quality of the rivers.