Even the advantages of the biofertilizers over the chemical fertilizers, it does not mean that these latter have to be substituted at 100%, because it depends of many factors in each case: soil status, percentage of NPK uptaken by the crop, etc…
The most habitual procedure of the farmers that use frequently or continually every season the biofertilizers, is to reduce the chemical fertilizers up to 60% or to substitute them when its price boosted, as it has occurred along 2008 and 2009.