Knowledge of nitrogen accumulation to the grains is of great importance for identifying breeding and growing strategies to improve cereal yield and quality. The aim of this study was to investigate post-anthesis N translocation in the spike and into different spikelets of two cultivars of spring wheat (Triticum aestivum L.) grown to maturity in solution culture. Sport (short grain filling time, low yield and high grain protein concentration) and WL (normal grain filling time, high yield and low protein concentration) were the cultivars used. Plants received stepwise declining rates of N on a daily basis, until 109 days after planting (DAP). Anthesis for cv. Sport was 92 DAP and for cv. WL 78 DAP. On seven occasions (from anthesis in cv. WL until maturity), 15N was given to selected groups of plants for 4 days. Then these plants were sampled and separated into plant parts. Spikelets and grains were separated according to spikelet position. Plant parts were weighed and analysed for N and 15N.

The N concentration in the grains was uniform for the spikelets in cv. WL but differed in cv. Sport. Final N concentration in a spikelet position was obtained at 126 DAP in cv. Sport and 112 DAP in cv. WL and was constant to the end of experiment at 154 DAP in cv. Sport and 147 DAP in cv. WL. A positive correlation between % atom excess 15N to spikelet position numbered from the base of the spike was exhibited in the lowermost part of the spike just after anthesis. Later, during grain filling, a negative correlation between % atom excess 15N to spikelet position was exhibited (−0·991 P=0·000). A positive correlation between % atom excess 15N to grain weight in the top of the spike was exhibited. Accumulation of 15N proceeded 14 days longer in the lowermost fertile spikelets than in the uppermost spikelets. It was concluded that the duration of N accumulation in the spikelets was dependent on spikelet position and uppermost spikelets had a shorter N accumulation period and contained lighter grains than lowermost spikelets.