Nitrogen supply - A determinant in water use efficiency of winter wheat grown under free air CO2 enrichment

Increasing N supply increased canopy size and decreased radiation transmission to the soil surface. Moreover increasing N supply enhanced biomass production from 771-1569 g m−2, ET from 227 to 336 mm and WUE from 4.07 to 6.20 g kg−1. Biomass was increased under [eCO2] by 17% among all N levels. [eCO2] increased soil moisture especially in the upper soil layer (0-20 cm) and thus irrigation was reduced under [eCO2] compared to [aCO2]. This effect was intensified by rising N supply leading to a significant CO2×N interaction on ET and WUE. Thus, the [eCO2] effect was for ET −2, −9 and −10% and for WUE + 20,+ 30 and +29% under 35, 190, 320 kg N ha-1, respectively. Simultaneously, there seems to be a greater increase of evaporation by [eCO2] under low than high N supply.