The fates of 15N fertilizer in relation to root distributions of winter wheat under different N splits

To optimize the nitrogen fertilizer management for high yield wheat production, field experiments were conducted to investigate the effects of nitrogen (N) splits on root growth, the fates of 15N fertilizer (recovery, residual, and loss), and grain yield in winter wheat (Triticum aestivum L.) from 2007 to 2009. The experiment site locates in the Middle and Lower Yangtze River Basin with frequent rainfall and higher groundwater table in China. 15N micro-plot experiment was designed with three N ratios of basal to topdressing as 30–70%, 50–50% and 70–30% at rate of 225 kg N ha−1, respectively. The results showed that root weight density increased with increasing share of basal N fertilizer before jointing. After jointing, root weight density in the 0–40 cm soil layer was the highest under an half N as topdressing. The fates of basal and top-dressed N showed significant differences. On average, the recovery and residual for top-dressed N were higher than those for basal N, whereas loss was lower. Moreover, the loss of basal N mainly occurred before jointing and contributed more to total N loss. Two years of data showed that half of N as basal fertilizer and half as top-dressing gave better root growth and increased plant N uptake and soil residual 15N, resulting in reduced loss of fertilizer 15N and hence improved grain yield.

► Root weight density in the 0–40 cm soil layer was the highest under an half N as topdressing.
► The recovery and residual for top-dressed N were higher than those for basal N, whereas loss was lower.
► The loss of basal N mainly occurred before jointing and contributed more to total N loss.
► The appropriate topdressing reduced N loss, increased plant N uptake and grain yield.