A study was undertaken to find out the possible cause for increase in the available K content under all the treatments including control in the on–going All India Coordinated Research Project on Long Term Fertilizer Experiments in operation since 1971. Seven treatments were selected viz. 50% NPK, 100% NPK, 150% NPK, 100% NP, 100% N, 100% NPK + FYM and control. A soil sample was also drawn from the fallow part of the field to represent the initial soil (i.e. of 1971). The study was carried out in wheat–maize rotation. Representative soil samples were collected at the beginning of the study and harvest of each crop. Plant samples were also collected from each crop. Laboratory analyses of forms of K, Q/I parameters, K fixation and release indicated the soil to be medium in K status. The non-exchangeable K content in this experimental field was found to be quite high and the kinetics of NEK release under different treatments recorded higher release rate constants. Also, significant positive correlation was found between release rate constants and crop K uptake, indicated the soil's ability to meet the crop K demand. The mineralogical study of the soil showed reduction in illite content, more so in plots treated with imbalanced dose of nutrients. This shows that to meet the crop K need opening of mica layer might have taken place to replenish the available pool and thus there has been no decline in the available K status of the soil. Instead it has shown increase in the K content in the present study, thus emphasizing the importance of using balanced and higher NPK doses to prevent the degradation of structural potassium.