Background Stalk lodging (breaking of agricultural plant stalks prior to harvest) results in millions of dollars in lost revenue each year. Despite a growing body of literature on the topic of stalk lodging, the structural efficiency of maize stalks has not been investigated previously. In this study, we investigate the morphology of mature maize stalks to determine if rind tissues, which are the major load bearing component of corn stalks, are efficiently organized to withstand wind induced bending stresses that cause stalk lodging. Results 945 fully mature, dried commercial hybrid maize stem specimens (48 hybrids, ~ 2 replicates, ~ 10 samples per plot) were subjected to: (1) three-point-bending tests to measure their bending strength and (2) rind penetration tests to measure the cross-sectional morphology at each internode. The data were analyzed through an engineering optimization algorithm to determine the structural efficiency of the specimens. Conclusions Hybrids with higher average bending strengths were found to allocate rind tissue more efficiently than weaker hybrids. However, even strong hybrids were structurally suboptimal. There remains significant room for improving the structural efficiency of maize stalks. Results also indicated that stalks are morphologically organized to resist wind loading that occurs primarily above the ear. Results are applicable to selective breeding and crop management studies seeking to reduce stalk lodging rates.

structural 19 Highlight: Maize stem morphology was investigated through an optimization algorithm to 20 determine how efficiently their structural tissues are allocated to withstand wind induced bending 21 stresses that cause stalk lodging.Abstract 24 Stalk lodging (breaking of agricultural plant stalks prior to harvest) results in millions of 25 dollars in lost revenue each year. Despite a growing body of literature on the topic of stalk lodging, 26the structural efficiency of maize stalks has not been investigated previously. In this study, we 27 investigate the morphology of mature maize stalks to determine if rind tissues, which are the major 28 load bearing component of corn stalks, are efficiently organized to withstand wind induced 29 bending stresses that cause stalk lodging. 30 945 fully mature, dried commercial hybrid maize stem specimens (48 hybrids, ~2 31 replicates, ~10 samples per plot) were subjected to: (1) three-point-bending tests to measure their 32 bending strength and (2) rind penetration tests to measure the cross-sectional morphology at each 33 internode. The data were analyzed through an engineering optimization algorithm to determine the 34 structural efficiency of the specimens. 35Hybrids with higher average bending strengths were found to allocate rind tissue more 36 efficiently than weaker hybrids. However, even strong hybrids were structurally suboptimal. 37There remains significant room for improving the structural efficiency of maize stalks. Results 38 also indicated that stalks are morphologically organized to resist wind loading that occurs primarily 39 above the ear. Results are applicable to selective breeding and crop management studies seeking 40 to reduce stalk lodging rates. 41 65 to devote to grain filling as compared to inefficient stalks (i.e., efficient stalks would have a higher 66 harvest index). 67As mentioned previously, both the taper and probable wind loading scenarios must be 68 defined to determine the structural efficiency of maize stalks. The wind load exerted on a plant 69 stalk, known as the drag force (Df), can be approximated as (Niklas, 2000):where ⍴ is the density of air, u is the local wind speed, Ap is the projected area of the structure, and 72 CD is the drag coefficient. While this equation appears fairly simple at first glance, it is 73 complicated by the fact that the variables on the right hand side of the equation are functions that 74 can vary both temporally and spatially. For example, the drag coefficient changes spatially along 75 the length of the stalk and is also a function of the local wind speed. As the local wind speed 76 increases, the angle of the leaf blades and tassel change (known as flagging), which alters the drag 77 coefficient. 78The strong interrelationships between the factors of Equation 1 complicate attempts to 79 directly measure wind forces on maize stalks. Direct measurements of wind speeds have 80 successfully been used to estimate drag forces in past studies of trees (Niklas and Spatz, 1999; 81 Niklas, 2000). However, t...