Composition and Morphology As Predictors of Stalk Strength.

For many years, researchers have observed that the stalks of bioenergy stalks become more susceptible to lodging as lignin content is decreased. Stalks that are readily digestible are therefore prone to lodging failure, while stalks that are resistant to lodging exhibit poor digestibility. An engineering analysis of the structural integrity of maize stalks indicated that stalk morphology has a larger influence on strength than composition. If this is true, the structural weakness caused by a decrease in lignin could potentially be offset by changes to stalk morphology, thus achieving stalks that are both digestible and lodging resistant. The purpose of this study was to experimentally assess the relative influence of morphology and composition. This study involved assessment of composition, morphology, and mechanical strength of three crops: dent maize, grain sorghum, and bioenergy sorghum. Composition was assessed via near infra-red (NIR) spectroscopy. Maize stalk morphology was assessed via x-ray computed tomography (CT scanning). Scan data was analyzed using a customized computer code which used image processing techniques to identify morphological features of maize stalk cross-sections. The morphology of sorghum stalks was assessed by measuring the major and minor diameters of each stalk with digital calipers. Three-point bending tests were used to measure the bending strength of all stalks. Multiple regression techniques were used to assess the contribution of morphological and compositional factors, both individually, and as groups. Morphological features were found to be stronger and more reliable predictors of stalk strength than chemical composition. These findings support the notion that a reduction in strength associated with changes in stalk composition can be compensated by changes in stalk morphology, thus suggesting new avenues for the development of robust bioenergy crops.