Can Changes in Canopy and/or Root System Architecture Explain Historical Maize Yield Trends in the US Corn Belt?

Continuous increase in the yield of maize (Zea mays L.) in the U.S. Corn Be-It 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 explarations and identified testable hypotheses for future research and crop improvement effort.