Sustainable agriculture production systems aim to maintain the stock of natural capital, but cropping in the Pampean Region can lead to natural capital degradation because evaluation of alternatives activities is done by simplified cost-benefits analysis, which neglects ecological cost and overestimates profitability. The objectives of this paper were: a) to quantify the soil natural capital degradation by means of main nutrient budget (Nitrogen, Phosphorus and Potassium) in the Pampean Region during the last 30 years and b) to analyse the variation in crop profitability when the nutrient reposition costs is incorporated in the conventional economical analysis. Nitrogen, Phosphorus and Potassium annual budget, was calculated for maize, soybean and wheat crops for each year of the 1970-1999 period, as the difference between exported nutrients (harvest) and those incorporated by fertilization for each year. Gross margin of these crops were recalculated including nutrients reposition costs. Nitrogen, Phosphorus and Potassium budgets of Pampean Region were negative for these three crops. Close to 23 millions of Ton of nutrients were lost, during 1970-1999 period, in the Pampean Region, being soybean crop responsible for 45,6% of this lost, wheat for 28 % and maize for 26%. Nutrients reposition costs of 1825 $.ha-1 for soybean, 697 $.ha-1 for wheat crop and 1461 $.ha-1 for maize for the 30 years studied were obtained. These figures represent the 20,6%, 20,0% and 18,7% of the average gross margins of the ’80 and ’90 on a constant price -bases for these crops. These results show that the cost benefit analysis application, during the “agriculturization process” in the Argentinean Pampean Region, hid an important cost of natural capital degradation overestimating economic profits. This points out a divorce between classical economic rationality adopted to select agricultural technologies and the possibilities of using ecological sustainability concepts to calculate the cost of activities in agricultural systems. To obtain progress towards sustainable agricultural systems the conventional economic analysis should be changed. This new approach will allow an integrative synthesis between ecology and economy goals.