Field Test Results of a New Device for Measuring Stalk Strength.

For plant breeders, the primary obstacle to achieving lodging-resistant crop varieties is lack of an objective method for assessing stalk strength. Counting the number of lodged plants per plot is common practice, but this indicator is severely confounded by weather. Rind puncture resistance is more objective than lodging counts, but can only differentiate between varieties with large differences in strength. This study presents the first broad set of field data for a new device capable of non-destructively predicting stalk strength with a high degree of accuracy

The device used in this study consists of a long lever arm that pivots about a stationary foot plate. The user places the pivot near the base of the stalk to be measured, steps on the footplate, and then pushes the stalk over, causing breakage. During the test, both force applied to the stalk and rotation of the arm are recorded. Structural engineering calculations are then used to determine both the stalk strength and flexural stiffness.

The experimental design consisted on 72 pre-commercial hybrid varieties of dent corn grown at 10 locations in the United States (courtesy of Monsanto Company). Plots consisted of 4 rows and about 20 plants per row. Stalks were sampled from the center two rows of each plot, with the 4 plants at the end of each row excluded from the study.

In agreement with laboratory results, flexural stiffness was reliably correlated with stalk strength (R² > 0.6. This is a valuable finding because flexural stiffness can be measured without damaging the stalk, thus enabling future studies on how stalk strength changes over time. A high degree of variation in stalk strength was found within individual plots, thus necessitating data analysis at the level of the entire experiment. A categorical analysis was performed with hybrid and location as the primary factors. After controlling for location effects, the 10 strongest hybrids were found to be statistically stronger than the 21 weakest hybrids at a 95% confidence level. Measured values of stalk strength were also found to compare favorably with internal Monsanto lodging scores for this set of hybrids. To the best of the authors’ knowledge, this represents the first time that any device has been successfully used to predict lodging susceptibility while also discriminating elite hybrid varieties on the basis of stalk strength.