To monitor water use with a capacitance probe installed in each plot to update the water use efficiency benchmark of 20 kg/ha/mm derived from French and Schultz.

• An increase of wheat grain yields released between 1957 and 2007 was found.
• Yields have increased because of improved harvest index, more biomass at flowering, and increased grain number.
• Nitrogen is critical in allowing each variety to reach its potential through increasing growth rate between stem elongation (GS31) and flowering.
• WUE has improved over the 1957-2007 timescale through increased yields, not greater extraction of water.