Continuous increase in the yield of maize (Zea mays L.) in the U.S. Corn Belt has involved an interaction with plant density. A number of contributing traits and mechanisms have been suggested. In this study we used a modeling approach to examine whether changes in canopy and/or root system architecture might explain the observed trends. A maize crop model was generalized so that changes in canopy and root system architecture could be examined. A layered, diurnal canopy photosynthesis model was introduced to predict consequences of change in canopy architecture. A two‐dimensional root exploration model was introduced to predict consequences of change in root system architecture. Field experiments were conducted to derive model parameters for the base hybrid (Pioneer 3394). Simulation studies for various canopy and root system architectures were undertaken for a range of sites, soils, and densities. Simulated responses to density compared well with those found in field experiments. The analysis indicated that (i) change in root system architecture and water capture had a direct effect on biomass accumulation and historical yield trends; and (ii) change in canopy architecture had little direct effect but likely had important indirect effects via leaf area retention and partitioning of carbohydrate to the ear. The study provided plausible explanations and identified testable hypotheses for future research and crop improvement effort.

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Maize (Zea mays L.) is among the most important grains contributing to global food security. Eighty years of genetic gain for yield of maize under both favorable and unfavorable stress‐prone drought conditions have been documented for the US Corn Belt, yet maize remains vulnerable to drought conditions, especially at the critical developmental stage of flowering. Optimum AQUAmax (Dupont Pioneer) maize hybrids were developed for increased grain yield under drought and favorable conditions in the US Corn Belt. Following the initial commercial launch in 2011, a large on‐farm data set has been accumulated (10,731 locations) comparing a large sample of the AQUAmax hybrids (78 hybrids) to a large sample of industry‐leading hybrids (4287 hybrids) used by growers throughout the US Corn Belt. Following 3 yr (2011–2013) of on‐farm industry‐scale testing, the AQUAmax hybrids were on average 6.5% higher yielding under water‐limited conditions (2006 locations) and 1.9% higher yielding under favorable growing conditions (8725 locations). In a complementary study, 3 yr (2010–2012) of hybrid‐by‐management‐by‐environment evaluation under water‐limited conditions (14 locations) indicated that the AQUAmax hybrids had greater yield at higher plant populations when compared to non‐AQUAmax hybrids. The combined results from research (2008–2010) and on‐farm (2011–2013) testing throughout the US Corn Belt over the 6‐yr period from 2008 to 2013 indicate that the AQUAmax hybrids offer farmers greater yield stability under water‐limited conditions with no yield penalty when the water limitations are relieved and growing conditions are favorable.

Water deficit during pollination increases the frequency of kernel abortion in maize (Zea mays 1.). Much of the kernel loss is attributable to lack of current photosynthate, but a large number of kernels fail to develop on water-deficient plants even when assimilate supply is increased. We examined the possibility that assimilate utilization by developing ovaries might be im-

HighlightComprehensive analysis of maize root phenotypes over the past century indicates that they have evolved to be more efficient in acquiring nitrogen.