The significant increases in shoot and grain DW with N3 treatment may be attributed to the delayed senescence of the root (e.g. higher root DW) and leaf (e.g. higher straw N concentration) during grain filling (Table 1), which, in turn, may maintain a greater capacity to take up N from the soil and a higher root-to-shoot transport of N for maximum grain yield (Borrell et al., 2001 and Mackay and Barber, 1986)