Stalk Lodging: Flexural Rigidity Is a Novel and Robust Predictor of Stalk Strength.

Regardless of genetic and environmental factors the culminating event of stalk lodging is structural failure of the stalk.  It naturally follows that stronger stalks are more resistant to stalk lodging. Unfortunately, accurately measuring stalk strength has proven problematic. We have observed that the most commonly employed measures of stalk strength produce inaccurate measurements and under predict strength by 40% to 60%. Furthermore, rind penetration resistance (a common measure of lodging resistance) produces failure modes unrelated to naturally lodged plants and is only weakly correlated with the chief structural engineering determinants of stalk strength. In this talk we present 1) a new testing procedure for assessing stalk strength that mimics the loading conditions and failure patterns of naturally lodged stalks, and 2) a robust, nondestructive predictor of stalk strength that is unaffected by changes in planting density, variety and location. 

Two replicates, of five commercial varieties of maize, grown at five planting densities and two locations (1000 stalks total) were submitted to a battery of tests to measure geometric and material features and stalk strength.  The equations of engineering mechanics were used to calculate each stalk’s flexural rigidity. Rind penetration predicted 18% of the observed variation in stalk strength whereas flexural rigidity predicted 81% of the variation in strength. The relationship between flexural rigidity and stalk strength was unaffected by changes in planting density, and hybrid type. Rind penetration resistance, on the other hand, was severely confounded by such factors. For example, the flexural rigidity regression model obtained from hybrid 1 can be used to predict 79% of the variation in strength of hybrids 2-5. Similar results are observed for changes in planting density, replicate and location.

Flexural rigidity appears to be a promising new selection index for stalk lodging as it can be measured rapidly without damaging the stalk.