Crop uptake of 15N labelled fertilizer in spring wheat affected by application time

Abstract

Time of nitrogen fertilizer application on crop recovery was studied in a field experiment at Foulumgaard, Denmark, in 2001. A solution of 15N-ammonium-15N-nitrate was applied in bands parallel to a single row of spring wheat grown in frames of 30 cm×40 cm. The labelled fertilizer was applied on 16 dates with intervals of 4–5 days from tillering to the start of grain-filling. Crop 15N recovery increased by 0.47%-point day−1 when the time of fertilizer application was postponed from tillering until the second node stage (GS32). On the other hand, a decrease in crop 15N recovery of –0.19%-point day−1 was recorded from GS47 to maturity (GS85–87). The effect of the 16 application times on 15N recovery was described by two straight lines having intersection at the time of full expanded flag leaf and ear emergence halfway (GS55). It was concluded that leaf area expansion is important for crop N demand and 15N recovery.