Because plants capture water and nutrients through roots, it was proposed that changes in root systems architecture (RSA) might underpin the three-fold increase in maize (Zea mays L.) grain yield over the last century. Here we show that both RSA and yield have changed with decades of maize breeding, but not the crop water uptake. Results from X-ray phenotyping in controlled environments showed single cross (SX) hybrids have smaller root systems than double crosses (DX) for root diameters between 2,465 and 181 um (P<0.05). Soil water extraction measured under field conditions ranged between 2.6-2.9 mm d -1 but were not significantly different between SX and DX hybrids. Yield and yield components were higher for SX than DX hybrids across densities and irrigation (P<0.001). Taken together, the results suggest that changes in RSA were not the cause of increased water uptake but an adaptation to high density stands used in modern agriculture. This adaptation may have contributed to shift resource allocation to the ear and indirectly improve reproductive resilience. Advances in root physiology and phenotyping can create opportunities to maintain long-term genetic gain in maize but a shift from ideotype to crop and production system thinking will be required.

Plants capture soil resources to produce the grains required to feed a growing population. Because plants capture water and nutrients through roots, it was proposed that changes in root systems architecture (RSA) underpin the three-fold increase in maize grain yield over the last century1,2,3,4. Within this framework, improvements in reproductive resilience due to selection are caused by increased water capture1. Here we show that both root architecture and yield have changed with decades of maize breeding, but not the water capture. Consistent with Darwinian agriculture5 theory, improved reproductive resilience6,7 enabled farmers increase the number of plants per unit land8,9,10, capture soil resources, and produced more dry matter and grain. Throughout the last century, selection operated to adapt roots to crowding, enabling reallocation of C from large root systems to the growing ear and the small roots of plants cultivated in high plant populations in modern agriculture.

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For 35 New Zealand soil samples of varied origin, estimates of total porosity and macro-porosity group were compared with measurements of these properties in an endeavour to judge the feasibility of making such estimates as part of the pedological field description.