What Do Maize Stalks Know about Structural Engineering?.

This study addresses the connection between maize stalk morphology and stalk strength. An engineering model of the maize stalk recently indicated that morphology is the dominant factor governing mechanical stresses. But do stalks “know” this?

An experiment was designed to collect further information about the morphology-strength relationship. A set of 5 commercial hybrids were grown at 5 different planting densities at 2 locations in Iowa with 2 replicates per location. At the time of harvest, a set of 10 stalks were sampled from each plot. Geometric data was obtained via high-resolution CT scanning. A customized computer code was used to extract over 40 different geometric features from the CT data. After scanning, stalks were tested in 3-point bending to determine strength.

Planting density was found to have a strong effect on stalk strength, which varied from 1.4 - 29.4 Newton-meters. The geometric feature most strongly correlated with strength was the cross-sectional area moment of inertia, which predicted over 75% of the variation in stalk strength. The coefficients of variation for stalk strength and area moment of inertia were 61% and 48%, respectively. Although stalk morphology and strength varied widely in this sample, a select number of geometric ratios were found to be nearly constant. For example, the ratio of area moment of inertia to cubed area was found to have a coefficient of variation of 1% while the ratio of major to minor diameter had a coefficient of variation of 3.6%. These quantities are similar to ratios that are used in engineering to predict the buckling of steel columns. Maize stalks therefore appear to be capable of adjusting their morphology to minimize the risk of failure and this adaptation is in accordance with engineering principles. Knowledge about how stalks naturally optimize strength could be useful for breeding purposes.