Abstract

The role of different organic N fractions in soils on nitrogen nutrition of rice and their inter-relationship with conventional soil test methods were investigated under field condition on alluvial soils of Thanjavur District in both Kuruvai and Theladi seasons. The changes in available N status due to cropping and N ferti lisation were monitored. These studies revealed that amino-acid fraction is quanti- tatively more important among the hydrolysable nitrogen forms for rice nutrition. The fixed NH, in the alluvial soil contributes about 6 per cent of total N and also significantly correlates with yield. The content of non-hydrolysable and unidenti- fied N forms, though quantitatively important are not directly related to the immediate N availability to the rice crop. The different forms of organic N are better related with organic carbon status than with KMnO,-N, leading to scope for improvement in the modification of these methods. Since N fertilisation and its transformation have a direct bearing with the changes in available N status, it is possible: to monitor the N fertility status of soil from the initial analysis as revealed from the study.

Keywords: