Nitrogen is the single most limiting factor for rice production. Detailed knowledge on nitrogen dynamics in rice fields is therefore of major importance for developing sustainable rice production. A field trial experiments was conducted in rainfed rice fields planted to three rice (Oryza sativa) cultivar; NDR-97 to investigate the influence of rice cultivars on nitrogen based fertilization on population size. Urea, DAP, Ammonium chloride, Ammonium nitrate were the fertilizers applied, at a rate of 100 kgNha”1 in three split doses. The experiment was laid out in a randomized complete block design with three replicate plots for each cultivar and treatment. The most probable number of methane oxidizing bacteria was estimated on six dates within the cropping period. It was observed that the NH4+-N µg g-1 dry soil content in soil was highest in urea fertilized NDR-97 at 20 DAS while NO3-_N content had highest at 80 DAS. Control soils (no N-fertilization) exhibited higher MCM population size than N-fertilized soils. Above conclusions were supported by measurements of MCM (methane consuming microbes) population size. The highest ammonium-N content was observed in urea (8.5 ± 0.71 µg g-1 dry soil) and lowest ammonium-N content in ammonium chloride treated plots (6.7 ± 1.5 µg g-1 dry soil) on 20 DAS. ANOVA indicated significant differences due to days fertilization and their interaction due to days × fertilization was also significant. The MCM population size was highest in control on 80 DAS (37.4 × 106 Cells g-1 dry soil) followed NH4Cl, NH4NO3, and urea treated soils. In case of fertilized plots the highest MCM population was highest on 80 (Urea 28.6 × 106 Cells g-1 dry soil; DAP 29.7 × 106 Cells g-1 dry soil; Ammonium nitrate 31.6 × 106 Cells g-1 dry soil and ammonium chloride 32.9 × 106 Cells g-1 dry soil) DAS and lowest on 20 DAS
Methane consuming microbes, Nitrogen fertilizers, Rice cultivars, NDR-97
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