Recovery of 15 N-ammonium- 15 N-nitrate in spring wheat as affected by placement geometry of the fertilizer band

Abstract

The time course of crop 15N recovery as affected by placement geometry of nitrogen fertilizer was studied in a field experiment. In frames of30 × 40 cm15N-ammonium-15N-nitrate was applied in bands parallel to a single row of growing spring wheat. The fertilizer was banded in nine treatments to a depth of 1.5, 5 or 10 cm combined with a distance from the crop row of 1, 5, 10 or 15 cm, or broad spread on the soil surface. The crop recovery of applied 15N was calculated on each of 9 sampling dates during the elongation phase. A sigmoid growth function was fitted, and the estimated parameters were analysed statistically. The maximum uptake rate was5.5–6kg N ha−1 day−1, and during an almost linear uptake phase of 7 days the crop recovered 68%of the maximum crop 15N recovery. Neither the maximum uptake rate nor the maximum crop 15N recovery was significantly affected by the treatments, whereas the start of the linear uptake phase was affected. By fertilizer placement at 5 cm depth the course of 15N uptake was delayed 0.5 day cm−1 increase in distance from the crop row. Uptake of ammonium nitrate placed on the soil surface or at a depth of 1.5 cm was delayed approximately 3 days compared to banding at 5 cm depth. This delay corresponded to the time until the first precipitation event. Maximum crop 15N recovery was obtained before anthesis and 20% of the recovered 15N was lost during the grain-filling period. In conclusion, the uptake rate of applied nitrogen was unaffected by placement geometry. However, the uptake course of applied nitrogen was delayed both by shallow injection and by increased distance between the crop row and the fertilizer band.