Bioassessment of Genotoxicity Due to Flux in Soil Nitrogen Dynamics Caused by Addition of Ammonium Nitrate

Plants can utilize soil nitrogen (N) as ammonium-N (NH4-N) or nitrate-N (NO3-N). Ammonium nitrate, an inorganic N fertilizer, having both forms of N, when added to the soil, causes an immediate change in the soil N dynamics. The ratio of ammonium to nitrate keeps changing and influences the soil pH and thus the rhizosphere environment sometimes making it toxic. To investigate the genotoxicity of ammonium nitrate fertilizer; Allium cepa L. was used as a model plant. A pot experiment was designed in which ammonium nitrate fertilizer was added to soil at the rate of 0.0, 0.2, 0.5, 0.8, 1 and 2 mg N g-1. Inorganic N nutrients in the form of NH4-N and NO3-N of soil samples and their ratio were investigated at 1, 7, 15, 30 and 45 days after treatment (DAT). Allium bulbs were also planted in each pot and three replicates were maintained for each dose of ammonium nitrate at 1, 7, 15, 30 and 45 DAT. Roots of Allium bulbs were harvested on the day 3 of sowing and fixed for cytological analysis. The result showed mitodepressive activity at higher concentrations of fertilizer, along with chromosomal anomalies which revealed the genotoxicity of ammonium nitrate. A significant positive correlation was observed between fertilizer concentrations and NH4 content of treated samples; similarly NO3 content also showed a positive correlation. The change in the ratio of NH4 to NO3 with respect to time and treatments are suggested as the possible reason for the disturbance in nuclear and chromosomal behavior.