Breeding progress is a major contributor to improved regional maize water productivity.

Agricultural water productivity, defined as the amount of grain produced per unit of available water, is an important sustainability criterion in modern crop production. Although genetic progress in maize has increased crop yields, there are limited studies on the role of plant breeding on this sustainability metric. In the center of the US corn-belt, maize rainfed yields have more than tripled since 1950 while relying on the same amount of water inputs. Our analysis shows that this shift in grain production resulted in a water productivity increase of 0.191 kg ha mm year, corresponding to a relative rate of 4.2% year, and is the result of both higher biomass productivity and increased harvest index (i.e., the proportion of grain in total crop biomass). The comparison of 61 historical maize genotypes commercially released for farmers in the region since 1934, throughout 28 individual experiments conducted over a period of nine years in which the effects of genetic shifts were individualized, shows that the genetic component of this increase was 1.9% year, representing 45% of the total gain. This positions plant breeding as a major technological contributor in the generation of more water productive rainfed cropping systems, reducing the need for additional agricultural freshwater to meet increasing societal demands.