Abstract
The nature and distribution of fixed ammonium and acid-hydrolysable N in seven soil profiles and surface samples of Aridisols representing the dominant soils of Western Rajasthan, India, were studied. The fixed NH4-N proportion of total N increased with depth in profiles and its content ranged 6.0-45.6% at different depths. A significant positive relationship was observed between fixed NH4-N and clay (r = 0.71, P < 0.01) and silt (r = 0.58, P < 0.01) contents. The total hydrolysable N proportion of total N varied from 48.9 to 87.4%at different depths and correlated significantly with clay content (r = 0.51, P < 0.01) and fixed NH4-N (r = 0.48, P < 0.01). From the regression equation relating fixed NH4-N to total acid-hydrolysable N, it was possible to predict fixed NH4-N content in these soils with a fair degree of accuracy. The C/N ratios when calculated from total acid-hydrolysable N remained more nearly constant with very small variations in depth than when calculated from total N or organic N where large variations were observed. The results of this study indicate that total acid-hydrolysable N is a useful index for fixed NH4-N and the nature of organic matter in these soils.
