Miscible Displacement of Nitrate and Chloride under Field Conditions
1977
Misra, C. | Mishra, B. K.
In an attempt to develop the capability for predicting the reduction loss of NO₃-N during leaching of nitrate fertilizers in an Oxisol field profile, a 2-cm pulse of Ca(NO₃)₂ solution containing 304 ppm of NO₃-N was displaced through a 300-cm by 300-cm field plot saturated with water down to the depth of 55 cm. On the following day an identical pulse of NH₄Cl solution containing 795 ppm of Cl was leached through the same plot. The results were analyzed by means of a convective diffusion type transport equation that incorporated an irreversible first-order sink term. The agreement between the observed and the theoretical breakthrough curves allowed the determination of the first-order reduction rate constant for NO₃-N as 0.1 hour⁻¹ at an average soil temperature of 34°C. Under these conditions, the recovery of added NO₃-N in the leachate was 70% whereas that of Cl was 100%, approximately, when the two pulses moved past the 55-cm soil depth. The apparent diffusion coefficients for NO₃-N and Cl were velocity dependent and ranged between 41 cm² hour⁻¹ to 80 cm² hour⁻¹, corresponding to the pore velocity range of 11.5 cm hour⁻¹ to 17 cm hour⁻¹. Although the present model was reasonably successful in predicting transport of ions undergoing microbial transformation in a natural soil, a more appropriate treatment should consider ion movement in stagnant and mobile phases in the soil pores in view of greater precision in working out the kinetics of biodegradable solutes.
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