Computational Models

Video-based measurements of maize stalk movement

Measuring the impact of brace roots on lodging resistance in maize.
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Top image: Two lodged maize with the roots pulled from the soil. Bottom image: A lodged maize in a field.
Lodged maize plants. Images from R.L. (Bob) Nielsen, Purdue University.

High winds can blow down crop plants, a process called lodging. This makes them difficult to harvest and can reduce yield of maize by 3-25%. While maize has specialized brace roots that anchor the stem and prevent lodging, it is unclear what extent the brace roots and root system contribute to lodging resistance due to the large number of factors involved in lodging. A newly developed method to quickly quantifying the effect of the brace roots on stem movement when subjected to dynamic loads.

Shaymaa Obayes, Graduate Research Assistant in the department of Civil & Environmental Engineering at the University of Delaware and colleagues assessed a novel technique to measure the root and stem displacement of maize subjected to wind using video-based measurements.

Three months after planting, 4 plants in the center-most portion of the 60ft by 30ft area plot were selected for testing. These plants were then subjected to wind using a high-speed fan.

A graphic of experimental field setup shows a fan blowing wind across four maize plants. Each plant has 5 target points highlighted at the same height along the route and stem. Two cameras capture their displacement and this information is fed to a digital management system represented by a computer.
Experimental setup for the Dynamic Monitoring Station used for video capture.

Displacement of the stem was determined multiple ways:

  1. solving theoretical equations based on engineering mechanics by portraying flexural behavior of maize as a cantilever beam based on Euler–Bernoulli beam,
  2. using the equation above and adding a term for stem rotation,
  3. employing a physics-based finite element model generated using ABAQUS software, and
  4. field testing a novel approach using digital image correlation algorithms to dynamically monitor displacement.

To employ the digital image correlation approach, cameras were used to capture 2-dimensional  displacement of targets attached along the stem and brace root.  Obayes explains the importance of this novel technique: “Using a high-speed fan in combination with the digital image correlation to capture dynamic deformations in a non-contact manner is an important advancement because it allows researchers to accurately monitor relatively small deformations without destroying the structure or the component. In addition, users can post-process data using the video-based imaging to measure plant characteristics near-instantaneously with no extensive effort. It was important to investigate structural modeling of the brace roots and root system behavior when subjected to dynamic loads like the wind since the maize on-farm is subjected to dynamic load.” Most research on stem mechanics employ a single point application of static force.

A graph showing stem height on the X axis and horizontal displacement in inches on the Y axis. Height location on the stem ranges from 2. to 17.5 inches. Horizontal displacement ranges from zero to 1.6 inches. Data from the digital image correlation method closely matches the theoretical engineering mechanics equation that includes rotation. Values from version 1 of the finite element model are accurate at lower on the stem but are greater than the digital image correlation values above 12 inches. All values of version 2 of the finite element model and the theoretical engineering mechanics equation without rotation are greater than the digital image correlation values.
Horizontal displacement vs. stem height comparison for a single plant using multiple techniques.

The authors found a 90% agreement between the finite element model and digital image-based displacement values. The agreement with the theorical equation including rotation in the stem and digital image-based values compared to the theorical equation without rotation highlight the importance of including rotation in calculations.

This approach can be used to develop targeted breeding strategies that strengthen plants to withstand unpredictable weather patterns and are more resilient to lodging.

READ THE ARTICLE:

Shaymaa K Obayes, Luke Timber, Monique Head, Erin E Sparks, Evaluation of Brace Root Parameters and Its Effect on the Stiffness of Maize, in silico Plants, 2022;, diac008, https://doi.org/10.1093/insilicoplants/diac008

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