Plant Populations of Modern Maize Hybrids AGRONOMY ARTICLE


Plant population considerations in modern Grain Maize Hybrids



  • Breeders have selected to increase grain yield in maize for generations.
  • Genetics that help plants sustain optimal kernel development under planting density pressure are present in modern maize hybrids.
  • Through modern breeding, maize plants have greater efficiency in converting nitrogen to grain, and adjusting ear size under stressed conditions.


Kernel Development

Yield components of maize, include ears per hectare, kernel rows per ear, kernels per row and kernel size, are influenced by genetics, agronomic practices, and environment. Genetic improvement and better agronomy are equally credited with increases in yield potential in the past 50 years, and more recently density studies are improving yield potential further. These yield advances are attributed to the ability of hybrids to increase grain yield and maintain photosynthesis during grain fill, leading to hybrids genetically disposed to produce more kernels. Environmental stress can lead to more barren plants or harvest problems with lodging but compared to older, open-pollinated varieties, modern hybrids consistently have greater yields and less lodging at high plant populations.




Nutrient utilisation

Barren plants are mainly caused by nutrient and drought stress. At greater populations, resources are assumed to limit plant growth; however, modern hybrids show greater nitrogen use efficiency and drought tolerance. Hybrids have been bred with a multi-gene integrated approach as drought tolerance depends on several genes and environmental conditions. Smaller root systems typically develop on plants grown at high densities and can limit the ability to reach nutrients, however, modern maize hybrids are able to efficiently take up and partition nutrients to developing ears.


Ear plasticity

Ear plasticity is the ability of flex, semi-flex and limited-flex or fixed maize hybrids to manage kernel development under different conditions. Hybrids with a greater degree of ear plasticity are able to increase ear size in response to lower plant densities. Determinate or 'fixed' ear type maize products typically have greater yields at high plant densities. Environmental aspects are also relevant as in drought conditions, a flex hybrid may be more adaptable to different weather scenarios, whereas in non-drought or higher yield potential conditions, a fixed hybrid at high density may optimise yields.




Fixed type: ability to maintain high number of kernel under high population.









Flex type: hybrid able to maximize kernel number in low plant population.


Progressive, modern genetics

Information from the Monsanto Learning Centre, US illustrates below how modern maize genetics have vastly increased yields across different planting densities (with the highest yields achievable at highest densities versus 40 years ago where highest yields were obtained at moderate densities).


Planted (seeds/hectare) 1970s Maize Product Modern Maize Genetics
 c. 40,000  5.07  10.54
 c. 70,000  6.33  14.84
 c. 99,000  3.67  17.00

Dekalb – leading the way in plant population genetics and density


Plant components, characteristics, and metabolism have improved and yield potential has advanced in Dekalb maize hybrids. These achievements are attributed to genetic improvements (in nitrogen uptake and use efficiency for example) as well as changes in management practices, allowing greater maize populations and fewer barren plants.


Grain yield potential appears to be optimal between 85,000 to 110,000 seeds per hectare; some hybrids realised optimal yield at the high end of this range while others had highest yields at lower seeding rates according to Monsanto trials data (2015-2017).


Unique product characterisation work being done in innovative planting density studies in Dekalb Technology Centres around Europe is now providing vital information and density recommendations to help farmers decide which maize hybrid and its optimal plant populations are best suited for particular soil conditions, water and nutrient resources. Dekalb are at the forefront of developing a leading, diverse portfolio of grain hybrids to answer all farmer needs and practices.