Effect of Leaching Fertilizer Salts on Convective Diffusion of Solute Ions in an Ultisol Profile

Solution pulses of NH₄O₃ and NH₄Cl containing 400 mg L⁻¹ of NH₄-N were leached in an acid soil (Haplustult) by sprinkling tubewell water with or without liming and in the presence or absence of a growing crop. Prolonged leaching resulted in a decrease of infiltration flux of water, presumably because of clogging of pores. In general, the volumetric water content was higher and the air porosity lower in the case of leaching in the limed than in the unlimed soil. The velocities of NO₃-N and Cl-appeared to be invariably higher than the corresponding solution velocities in both the cases indicating that ions move through some preferred pore sequences. The velocity of NO₃-N appeared to increase up to 0.5 m soil depth but remained nearly uniform thereafter. The values of convective diffusion coefficient were two to four times that of the velocities of NO₃-N under unsaturated condition.