Barley Stem Bending Resistance Declines During Maturation, Then Peaks in Ripe, Dry Plants

Area of Science:

• Agricultural science
• Plant physiology
• Biomechanics

Background:

• Stem lodging in barley (Hordeum vulgare) is a major agricultural concern, reducing yield and harvestability.
• Lodging occurs when wind and ear weight exceed the stem's (culm's) load-bearing capacity.
• Culm strength is influenced by geometry and material properties, decreasing with plant height.

Purpose of the Study:

• To investigate the changes in barley stem mechanical properties during ripening.
• To identify the physiological window of maximum stem lodging risk.
• To understand the impact of moisture content on culm strength.

Main Methods:

• Assessed stem mechanical properties using a three-point bending test on two barley genotypes.
• Analyzed stem segments at three positions along the culm.
• Evaluated changes in culm strength, area moment of inertia, and apparent material strength during ripening and drying.

Main Results:

• Culm strength slightly diminished during ripening due to decreased area moment of inertia and material strength, likely from turgor loss.
• Stem strength increased to a maximum when ripe segments were dried to harvest moisture content.
• Minimum stem bending resistance occurs in a window when plants are fully ripe but not yet harvest-dry.

Conclusions:

• The physiological risk of stem lodging is highest when barley is fully ripe but not yet harvest-dry.
• Actual lodging risk increases as harvest approaches due to frequent storms and reduced strength of wet, dry straw.
• Understanding these dynamics is crucial for optimizing harvest timing and mitigating crop losses.