Transformation and movement of band-applied nitrogen fertilizers in several Manitoba soils

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Pang, Patrick Chi-Kee
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The transformation, effect on soil pH and movement of nitrogen from banded nitrogen materials (urea, ammonium sulfate and ammonium hydroxide) were studied in three Manitoba soils of different initial soil pH values. The greatest effect on soil pH took place near the fertilizer zone, but the magnitude of the change varied greatly depending on soil characteristics. Irrespective of the fertilizer materials, the oxidation of ammonium form of nitrogen was the slowest with acid Keld soil (pH 5.4). Nitrification with neutral Wellwood II soil (pH 6.6) was rapid, with a high accumulation of nitrite taking place, when band-applied with 800 kg N/ha of urea and NH4OH. With alkaline Morton soil (pH 8.2), oxidation of the ammonium form of nitrogen to nitrate was rapid without any accumulation of nitrite. The oxidation of band-applied (NH4)2SO4 was slow in these three soils. The difference in nitrifying capacity among the three soils was related to the initial nitrifier numbers whose activities were affected by the initial soil pH... Diffusion coefficients of ammonium in the soils were dependent upon the types of soil, nitrogen material, temperature and rate of application. Generally, the smaller diffusion coefficient restricted movement of ammonium away from the zone of application and therefore retarded the transformation to nitrite and nitrate.