SPATIAL DISTRIBUTION AND INFLUENCE OF N-FERTILIZER ON MOB POPULATION IN THREE DIFFERENT IRRIGATED RICE AGROECOSYSTEMBHARTI SINGH, DEEPMALA KATIYAR AND RAJVEER SINGH CHAUHAN
Variation in methane oxidizing bacterial population size due to rice varieties was investigated during July-November 2009 in irrigated rice varieties NDR-80, Pant Dhan-10 and Sarjoo-52. Bare, bulk and Rhizospheric were sampled for the analysis of NO3-N, NH4-N and MOB population for each variety. The observations were made during 20 to 120 days after transplantation (DAT). The fertilizer selected for the experiment was urea and was applied in three split doses (40:30:30 Kg Nha-1) to all rice varieties. The experimental design was consist of: (a) Bare 6 plots (3 plots unvegetated, 3 unfertilized plots), (b) Bare fertilized (3 replicate plots for each unvegetated) (c) vegetated plots for each variety (9 plots, 3 replicates for each variety unfertilized) and (d) vegetated fertilized (9 plots, 3 replicate plots for each variety). Results showed that there was significant difference in growth variables for all rice varieties due to growth period and fertilization. The ammonium -N and nitrate-N was higher in fertilized plots than unfertilized plots. Among varieties Pant Dhan-10 had maximum ammonium -N, nitrate-N followed by NDR-80 and Sarjoo-52. The MOB population higher in unfertilized and fertilized plots from 80-120 DAT across soil type (Bare, Bulk and Rhizosphere) of all varieties. The MOB population range from 3.1 to 60.1 × 106 cells g-1 dry soil) across varieties, treatment and days. The growth variable (Root Biomass and Shoot Biomass) were higher in fertilized plots than unfertilized plots. Among varieties shoot biomass was highest in NDR-80. The highest root biomass was recorded at 100 DAT. Root biomass was highest in Pant Dhan-10 lowest observed for Sarjoo-52. The ammonium- N, nitrate-N was highest in bulk soil of Pant Dhan-10 (11.2 ± 0.28 μg g-1 dry soil) on 20 DAT. There were significant differences in MOB population size during the study (p<0.05). In case of Sarjoo-52 rhizosphere soil, the highest MOB population ( 60.1 × 106 cells g-1 dry soil) on 120 DAT and lowest on 20 DAT in rhizospheric soil of three varieties (NDR-80 rhizosphere 12.0 × 106 cells g-1 dry soil; Pant Dhan-10 rhizosphere 13.1 × 106 cells g-1 dry soil; Sarjoo-52 rhizosphere 17.3 × 106 cells g-1 dry soil). In the bulk soil of two varieties exhibited highest MOB population on 100 DAT. Whereas in case of vegetated fertilized soil type Sarjoo-52 rhizosphere has the highest MOB population than bulk soil. The MOB bacterial population size in control (unfertilized) plots as well as the fertilized plots was highest at 80-120 days and lowest on 20 days. Among control and fertilized plots the MOB populations were highest in control and lowest in fertilized plots.
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