A growth chamber study was carried out to determine crop utilization of nitrogen added as 15N-labelled calcium nitrate or urea to eight Manitoba soils of diverse characteristics. Dry matter yield of wheat was significantly greater where calcium nitrate was used as a nitrogen source than when urea was the nitrogen source in Pine Ridge, Wellwood, and Granville soils. Residual nitrogen in the soil at the end of the experiment was greater where urea was used than where calcium nitrate was used. Total recovery of urea nitrogen generally exceeded recovery of nitrogen from calcium nitrate. In a laboratory study it was found that more of the nitrogen added as urea or ammonium sulphate was retained than when nitrogen added was as calcium nitrate. Rapid ammonium fixation from ammonium-yielding carriers occurred, especially in the Granville and Waitville soils. Ammonium fixation could be one reason for the higher utilization of nitrogen from nitrate than from ammonium sources.
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Hedlin et al. (1986) studied this question.
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