Distribution of Fixed Ammonium in Relation to Soil Characteristics in Some Soils of Punjab

The fixed NH₄-N and C/N ratio of seven benchmark soil profiles of the state of Punjab were studied. The contents of native fixed NH₄-N showed large variations among the soil series but relatively smaller differences between horizons of the same profile. From 21 to 87% of total N was present as fixed NH₄-N, higher percentage of the latter being invariably observed at lower depths. A significant negative correlation between fixed NH₄-N and organic carbon (r = −0.57 to −0.89) is observed in all the profiles. That a bulk of fixed NH₄-N is associated with finer textural fractions of the soil is evident from a positive correlation of it with clay (r = 0.44 to 0.91) and silt (r = 0.39 to 0.89) and a negative one (r = −0.49 to −0.92) with coarse fraction. Narrowing of C/N ratio with depth is attributed to fixed NH₄-N in soil. The C/N ratio in the profiles varied much less with depth.