Effects of nitrogen application at different developmental stages on nitrogen accumulation and translocation in winter wheat

A series of pot and field experiments were carried out to estimate effects of nitrogen application at different developmental stages on uptake, translocation and partitioning of nitrogen in wheat（Triticum aestivum . L）using 15N trace methods. A Multi-spikelet cultivar, Yumai49-198, and a big-spikelet cultivar, Lankao Aizao8, were adapted as test materials. The results showed that grains had the highest nitrogen content compared to other plant organs at maturity. Partitioning proportion of nitrogen among different plant organs was: grains ＞stems and leaf sheaths + leaves＞glumes + rachis. The maximum N accumulation was observed in treatments with nitrogen top-dressed at jointing stage. The highest partitioning proportion of nitrogen in grain was observed in the treatment with nitrogen top-dressed at heading stage, while for root was observed in the treatment with nitrogen total basal application. The results also showed that amount of 15N uptake accounted for 16.45~26.6% of the total nitrogen. The maximum uptake appeared in Nb treatment（nitrogen was applied at reviving stage）for Lankao Aizao 8 and in Nc（nitrogen was applied at jointing stage）for Yumai 49-19, respectively. With delaying of N application date, the rate of nitrogen assimilation and N contribution to grains after anthesis increased. The contribution of N translocation rate to N accumulation in grain in pre-anthesis was higher than in post-anthesis. However, the contribution of labeled N assimilation post-anthesis to grain nitrogen accumulation was higher than that translocation from pre-anthesis。In conclusion, top addressing N at jointing stage was recommend in our study area considering grain yield and protein content in grain.