A study was carried out in the North of the State of São Paulo during a five year period (1973/78) in the cerrado soil at three localities to study yields of soybeans with the application of different levels of potassium. The potassium in the form of potassium chloride was applied in the rows at planting time only in the first year and in subsequent years only residual effect was studied. At the three localities no significant increase in yield of soybeans was observed nor were there differences in concentration of K in leaves in any of the years. Chemical analysis were made to determine exchangeable K, nonexchangeable K with could be released and total soil K. The soil mineralogical analysis showed the nonexistance of potassium reserves. Low exchangeable K and nonexchangeable K and good yields of soybeans indicated that soybeans have great capacity to extract potassium from the soil and the critical level usually established at 0.12 meq/100 g in the soil for soybean crop could probably be lowered to approximately 0.08 meq/100 g in cerrado soil for cultivars with 140 or more days maturity.