ROLES OF OXIDISED AND REDUCED NITROGEN AEROSOLS ON PRODUCTIVITY OF WINTER RICE (Oryza sativa L.) CROP
Abstract
In a pot culture (2011), aerosols of oxidized nitrogen (NaNO2) @20kgha-1yr-1 (≈200 ppm), reduced nitrogen (NH4Cl) @10kg-1hayr-1 (≈100 ppm) and distilled water (control) were sprayed (1500 cm3plant-1) weekly at different days after sowing (DAS) to study their impacts on physiology of rice varieties (Bishnuprasad, Kanaklata, Joymati, Jyotiprasad and Mulagavaru). In a field trial (2012), the simulated N-aerosols @ 20 & 40 kg ha-1y-1 of each (1000 cm3m-2) along with a control were misted to population of the rice variety, Kanaklata at four different growth stages viz., germination and tillering (0-30 DAS), maximum tillering, (30-60 DAS), panicle initiation (60-90 DAS) and reproductive development (90-120 DAS). In both pot and field experiments, the N- aerosols brought about wide differences in net photosynthesis rates, nitrate reductase activity, nitrogen use efficiency (NUE), membrane permeability in the crop. The aerosols with lower doses at earlier growth stages influenced NUE and economic yield of the crop varieties. Mechanisms of altering membrane permeability either by depletion of Ca2+, or acceleration of peroxidase activity of cell in presence of the aerosols have been elucidated.
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Introduction
Crop plants suffer from oxides of nitrogen (NO, NO2 and N2O or NOx) and reduced ammonia (NH3 or NH4+) in rapidly growing urban and peri-urban areas (McClean et. al. 2011, Bharali et al., 2012). Nitrogen dioxides form week acids in the extra-cellular water and dissociate into HNO2 and HNO3 to produce nitrate, nitrite and protons (Zeevart, 1976). A concentration of NOx >10µll-1 alter physiological processes including N assimilation (Darrall, 1989). Ammonia at concentration >1mM in plants causes death of tissues in plants (Mehrer and Mohr, 1989).
In field, farmers apply fertilizers in nitrate and ammonium forms. These are very mobile in soil. Crop plants are able to utilize only 30-40% of applied nitrogen (Raun and Johnson, 1999). We have discussed here the tolerance mechanism(s) of rice to aerosols of nitrogen.