Nitrogen and Dry Matter Accumulation, Remobilization, and Losses for Mediterranean Wheat during Grain Filling

Dry matter and N accumulated by winter wheat ( Triticum spp.) plants until anthesis are of importance under a Mediterranean climate because yield greatly depends on translocation of pre‐anthesis assimilates to grain. This field study was conducted to assess the effect of N fertilizer and cultivar on the amount of pre‐anthesis dry matter and N accumulated and remobilized, and the possible N losses. Two bread ( T. aestivum L.) and two durum ( T. durum Desf.) wheat cultivars were grown in a silty clay (Typic Xerorthent) in 1986 and 1987. Nitrogen at a rate of 150 kg ha −1 was applied before planting or 100 kg N ha −1 was applied before planting and then 50 kg N ha −1 at early boot stage. Cultivar dry matter translocation efficiencies ranged from 2.3 to 36.4%, N‐translocation efficiencies from 60.9 to 80.7%, and the contribution of pre‐anthesis assimilates to grain from 6 to 73%. Split N application reduced the contribution of pre‐anthesis assimilates to grain. High amounts of N (>200 kg ha −1 ), which had accumulated by anthesis led to net N losses at maturity, even with high yields (>6 Mg ha −1 ). No N losses were observed when N content at anthesis was lower than about 150 kg ha −1 . However, at values ranging between these upper and lower limits, N loss was yield dependent (only yields >8 Mg ha −1 prevented N losses). Split N application tended to reduce N losses. Results indicated that the greater the amount of dry matter and N accumulated before anthesis, the higher the translocation rates of dry matter to grain and the greater the risk of net N losses at maturity.