The general trend shown by the N budget was a higher N loss in the PS45 plots than the N300 plots (Table 5). However, these data could be misinterpreted because, as previously reported [47], NHþ4 eN can be fixed in the interlayers of the clay minerals. Daudén and Quílez [2] found that the immobilization and/or fixation of N when using PS fertilizers could play and important role in the N budget under similar climatic conditions.