Movement and Distribution of Ammonium-N Following Deep Placement of Urea in a Wetland Rice Soil1
- N. K. Savant and
- S. K. De Datta2
The vertical distribution of NH4+-N following subsurface placement of different forms of urea was studied in incubated, undisturbed wetland soil cores. For prilled urea, supergranule urea, and prilled urea in mudballs placed at the 10-cm depth, peak concentration of NH4+-N was near the placement site and decreased with time, whereas after placement of sulfurcoated urea (SCU-21) at the same depth, peak concentration of NH4+-N increased over a period of 4 weeks. With time, the NH4+-N tended to move downward more than upward from the placement sites, probably because of the mass flow of percolating water.
In another experiment, the movement and spatial distribution of NH4+-N were studied following application of 2-g supergranules of urea (SGU) and sulfur-coated supergranules of urea (SC-SGU) at a depth of 10 cm in transplanted and cultivated wetland fallow plots. After 2 weeks, NH4+-N concentration gradient for SGU was 1,850 to 32 µg N/cm3 wet soil, over a distance of 10–12 cm from the placement site. The corresponding gradient for SC-SGU was 287 to 32 µg N/cm3 wet soil, over a distance of 5–7 cm from its placement site. For SGU in transplanted plots, the concentration gradient decreased steadily through 8 weeks, whereas for SC-SGU it increased during the first 4 weeks and then decreased. The disappearance of NH4+-N with time and distance from the site of application is attributed to diffusive transport or convective transport, or both, and root-sink effect. The general movement of NH4+-N was downward > lateral > upward. The apparent benefits of deep placement of urea in a wetland rice soil are discussed.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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