Asian Journal of Soil Science and Plant Nutrition

Aims:  Our understanding of how different fertilizer sources affect root air space formation and subsequent nitrogen transformation rates in rice soil remains limited. An experiment was conducted in rice fields using the VL Dhan158 cultivar to examine how different nitrogen-based fertilizers affect rice root porosity, nitrogen mineralization rates, nitrification, and nitrifier population size.

Study Design: The study employed a completely randomized block design in triplicate. Experimental plots received either urea, ammonium nitrate, or ammonium chloride at 100-kg N ha^-1 in three split doses, of 40 kg N ha^-1 soon after planting, followed by 30 kg N ha^-1 during both the active tillering and flowering phases. VL Dhan 158 seeds were dibbled (4-6 seeds per hill) into each plot, maintaining 20 cm between rows and 15 cm between hills, with an untreated control for comparison.

Place and Duration of Study: The experimental plots were established in the Jeoli village cluster of the Hawalbag block, lying between the coordinates of 29° 36' and 29° 38' N latitude and 79° 34' and 79° 36' E longitude. This region has a dry tropical climate with pronounced monsoon features.

Results: The control group exhibited the lowest rates of N-mineralization, nitrification, and nitrifier population, followed by urea, NH₄NO₃, and NH₄Cl in ascending order. Conversely, plant growth vigor, grain yield, and root porosity were highest for NH₄Cl, followed by NH₄NO₃, urea, and the control. A significant relationship was found between the population of nitrifying bacteria and the rate of N-mineralization, as well as root biomass and root air space. The various fertilizer sources led to significant differences in aerenchyma tissue development, resulting in varying degrees of rhizosphere aeration. This variation explains the differences in nitrifier populations supported by VL Dhan 158 under different fertilizer treatments and the subsequent variations in soil processes.

Conclusion: The study concludes that fertilizer selection impacts both nitrifier population and their functions. The effectiveness in ranking of fertilizers with respect to present study is ammonium chloride>ammonium nitrate>urea>control. Efficient management and synchronization of soil nitrogen transformation involves selection and application of ecofriendly sustainable fertilizer type that support nitrifying bacteria in rice rhizosphere and soil so that nitrogen is accessible to rice plants during growth and consequently improve the grain yield.