Stickstoffbilanz von 15N-Harnstoff bzw. 15N-Ammonsulfatsalpeter mit Dicyandiamid in Gefäßversuchen zu Grünhafer und Sommerweizen

Recovery of Nitrogen of ¹⁵N-urea and ¹⁵N-ammonium sulfa-nitrate with addition of dicyandiamide in pot trials with green oats and spring wheat In pot trials with green oats and spring wheat, the effect of ¹⁵N-urea (UR) and ¹⁵N-ammonium sulfa-nitrate (ASN) with addition of the unlabelled nitrification inhibitor dicyandiamide (DCD) was investigated on the basis of equal amounts of N by fully taking into account the DCD-N, with respect to yield, N-removal, distribution of ¹⁵N in plants and soil (sandy loam, pH 6.5) as well as the fate of DCD.

• 1 In Neubauer experiments with green oats, 62–69% of fertilizer-N were found in the shoots, 21–31% in the roots and 4–9% in the soil. In Mitscherlich trials with spring wheat, 85–88% of fertilizer-N were found in grain and straw, 7–10% in the roots and 3–4% in the soil. ¹⁵N-recovery, in all cases was between 98-100%, thus exhibiting pratically no loss in course of the experiment.
• 2 Yields of green oats (shoots), resp. spring wheat (grain and straw) were about 4-11 % lower in pots with DCD; on the contrary, N-contents and removal were somewhat higher compared to control without DCD.
• 3 With conditions given by these pot trials (strong root penetration, favourable temperature, repeated supply during early growth, slow soil-specific decomposition), water-soluble DCD was taken up partly by the plants and appeared mainly in leaves resp. straw. In grains of spring wheat, DCD-contents were, however, very low (maximum 3 ppm DCD-N); in roots it could not be detected. In comparison, analysis of crop-material in field trials showed no DCD in grains and only very few ppm DCD in straw.
• 4 In pots with DCD, the residual-N in the soil was higher, probably because of the prolonged time of reaction between ammonium and the organic matter of the soil.