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Fertilizer N recovery in crop production systems seldom exceeds 50%. Two long-term winter wheat (Triticum aestivum L.) experiments were selected for use of 15 N to evaluate fertilizer recovery in the grain, straw, and soil. Each experiment included variable nitrogen rates that had been incorporated preplant each year for >20 yr. In 1988, ammonium nitrate enriched with 11.888 atom % 15 N ( 15 NH 4 15 NO 3 ) was applied to microplots within the main plots of these long-term experiments. Conventional ammonium nitrate (0.366% 15 N) was added to the microplots the following 2 yr to allow measurement of residual effects of the enriched fertilizer. Three years after the 15 N microplots were established, soil cores (0.025 m in diam.) were taken to a depth of 1.20 m and partitioned into 0 to 0.15, 0.15 to 0.30, 0.30 to 0.45, 0.45 to 0.60, 0.60 to 0.90, and 0.90 to 1.20 m. From all microplots, percentage 15 N recovered in the grain and straw at harvest and in the soil was determined and expressed as atom % excess corrected for background abundance. Total fertilizer N recovery ( 15 N removed in the grain and straw plus that remaining in the soil) decreased with increasing N application at both locations. Results from this study combined with previously published findings from these locations suggest that fertilizer N recovery was greater where there was: (i) no evidence of priming (increased net mineralization of organic N pools when low rates of fertilizer N are applied); and (ii) reduced soil-plant buffering (N that can be applied in excess of the amount needed for maximum yield without resulting in increased soil profile inorganic N accumulation). |
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