Author(s):

Bikha Timung and Bhagawan Bharali

Abstract: Rice grown in Assam suffers from intermittent deficit of water in upland condition during Rabi season (January to May). The ailment caused by water stress of rice crop can be judged at subclinical level incorporating some of the biochemical changes in plants at different growth stages of the crop. Nitrogen in leaf is one of the key parameters involved in many physiological processes e.g chlorophyll formation modulating the rate of photosynthesis in plants, and it is restrained by drought stress in crops. SPAD (soil plant analysis development) values measured by chlorophyll meter are the yardstick for judicious application of nitrogen fertilizer for enhancing N status in rice crop in situ. Fixed time nitrogen management (FTNM) is considered as a useful tool practised in rice crop. As per FTNM, 40KgNha^-1 was applied as basal, and subsequent dose of nitrogen was applied according to the critical need of the crop, determined by the SPAD values against a control without basal N. Thus, the cumulative nitrogen received by the crop in the situation of physiological drought (No water+ 5000ppm of 6000PEG spray at tillering and heading stages against normal irrigation) was 140kgha^-1. Five traditional upland genotypes (Mipholong, Balam, Sok Langlu, Sovak and Inglongkiri) were incorporated in the studies, where Inglongkiri emerged as the most physiologically efficient genotype. It was enriched by the sound biochemical features viz., higher leaf N(1.7-2.5% %), NR activity (480-501 µmoleNO₂- g^-1 f.w. hr^-1), proline content (261-326 µgmol-1g^-1 f.w.), total carbohydrate content (9.8-11.3mg g^-1 d.w), Pⁿ rate (10.8-12.4µmolesCO₂ absorbed m-²sec^-1) envisaged by the higher SPAD values (32 to 32) irrespective of drought and unstressed plants.

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