INORGANIC NITROGEN MOVEMENT IN TROPICAL SOILS : II. The Fate of Ammonium Fertilizer in Well and Poorly Drained Soils in the Rainy Season

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The movement and recovery of ammonium nitrogen down the profile of a fallow clay soil with poor drainage were studied during the rainy season in the Philippines. Cylinders were either covered by film or uncovered to determine the effect of rain. After 4 months with a total rainfall of 850 mm, 20 and 40% of the applied N was recovered from the 0-75 cm soil in uncovered and covered cylinders. Downward movement of ^<15>N was found in both covered and uncovered cylinders. The ^<15>N content of the soil layers lower than 45 cm depth, where soil was frequently submerged, was negligible. A similar experiment was conducted in a dryland clay-loam soil with better drainage. After 5 monthes with a total rainfall of 890 mm, 24 and 63% of the applied ^<15>N was recovered from the 0-75 cm soil in uncovered and covered cylinders. Labeled nitrogen was traced up to the 75 cm depth in both cylinders. In uncovered cylinders, downward movement of ^<15>N as mineral nitrogen was more pronounced in the well-drained than in the poorly drained soil, while the reverse was the case in the covered cylinder. The observed difference in nitorogen recovery in two dryland soils is discussed in terms of possible mechanisms of loss.
社団法人日本土壌肥料学会の論文