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Abstract Potassium (K) fertilization is important to maintain adequate concentrations of plant available K in agricultural soils to achieve best yields and improve crop stress tolerance and water‐use efficiency ( WUE ). Water‐use efficiency ( WUE ) can be expressed on various spatiotemporal scales, and it is known that responses of WUE to external stress are not uniform across scales. Multiscale evaluations of the impact of varying K fertilization on the WUE of C 3 crops under field conditions are missing so far. In the present field study, we evaluated effects of K fertilization on WUE of sugar beet ( Beta vulgaris L.) on short‐termed leaf‐ ( WUE L eaf ) and canopy‐scales (WUE Canopy ) and as the agronomic ratio of white sugar yield ( WSY ) to in‐season water use (i.e. WUE WSY ). In K‐fertilized plots, WUE WSY was enhanced by 15.9%. This effect is attributed to increased beet yield and WSY , as no differences in total in‐season water use between fertilized and unfertilized plots were observed. Potassium (K) fertilization significantly enhanced the leaf area index, resulting in a more efficient depletion of soil moisture by roots in K‐fertilized plots. As a consequence, WUE L eaf was increased due to stomatal adjustment. Potassium (K) improved WUE C anopy only by tendency. It is concluded that K fertilization improves the WUE of field‐grown sugar beet across scales, but processes that regulate WUE are highly scale dependent.
Jákli et al. (Tue,) studied this question.