Abstract
Availability of nitrogen (N) to plants depends on the rate of mineralization of organic N in soil. Liming influences availability of N; and uptake of N by a growing plant in a particular time is not only controlled by the plant type itself but also by the microenvironment of rhizosphere which influences different N- transformation processes in soil. The present investigation was, therefore, conducted to make a relationship of changes in different forms of organic N in an alluvial acid and the corresponding limed soils with cropping and N fertilization. Results reveal that irrespective of soils, cropping and N-addition, in general, the amount of organic forms of N decreased with increase in the period of investigation. Furthermore, the amount of different forms including hydrolysable NH4+ and amino acid- N were maintained in higher amount in cropped over the uncropped system suggesting that presence of plant influences the micro-environment of rhizosphere soil. The congenial atmosphere created in rhizosphere soil in presence of maize leads to the release of higher amount of hydrolysable organic N in cropped situation. As the organic and inorganic form of N in soil are inter-convertible within themselves, the utilization of inorganic N by maize crop is replenished by different fractions of organic N released through mineralization and thus comparatively higher amount of different forms of N are accumulated in limed over the corresponding unlimed soil. But the amount of serine + threonine-N, unidentified N and non hydrolysable fraction of organic N did not show any definite trend of results.

Key words: Acid soil, Limed soil, inorganic N, Organic N.