Abstract: High plant density is one of the cultivation measures for high yield in maize production, but may risk lodging during the growing period. The occurrence of lodging is highly related to stalk mechanical intensity in addition to plant height and stalk diameter. Some investigators have measured the indices of stalk intensity in maize, but we believe that the knowledge on bending properties of maize stalk will give more mechanical explanation to lodging-resistance. In the present experiment, we employed three maize cultivars, Denghai 3719 (high density-tolerant and lodging resistant), Jingke 519 (low density-tolerante and lodging resistant), and Nongda 108 (moderate density-tolerant), and used universal hydraulic test equipment to investigate the Yong’s modulus and the bending strength of stalk under five densities (3.00, 5.25, 7.50, 9.25, and 12.00 × 104 plants ha-1, respectively). The basal 1st to 8th internodes of 3–8 plants from each treatment were sampled at pre-tasselling and dough stages, respectively. The parameters of stem morphologic trait showed thinned internode diameter and longer internode at basal stem accompanying with the increasing of maize planting density in all three cultivars, in which Denghai 3719 had the smallest values (internode diameter and length). The moment of inertia of maize stalk varied among cultivars and among internodes, and close related to internode diameter. The Yong’s modulus and bending strength of maize stalk increased in the process of growth period, but decreased significantly with the increasing of planting density and the rising of internode position. The Yong’s modulus and the stalk bending strength on the average of the 3rd and 5th internodes were 72.32 MPa and 4.05 MPa in Denghai 3719 at pre-tasselling stage, while only 42.31 MPa and 2.80 MPa in Jingke 519 which were the stalk broken thresholds in high densities (7.5–12.0 × 104 plants ha-1). They went up by 100.8% and 129.3% in Denghai 3719 and 59.1% and 105.7% in Jingke 419, respectively at dough stage. The results imply that the probable critical parameters of stalk broken are 40.0 MPa for Yong’s modulus and 2.8 MPa for maximum bending strength at basal internodes at pre-tasselling stage in maize. The Yong’s modulus of stalk was significantly correlated (P<0.01) with the bending strength. While the diameter of internodes was positively correlated (P<0.01) with Yong’s modulus and bending strength of stalk at pre-tasselling stage, but not at dough stage. They were negatively correlated at P<0.01 with field lodging per-centage. The Yong’s modulus could reflect the ability of tolerance to high densities of stalk, and the bending strength of stalk to lodging resistance, however, the diameter of internodes was not a good indicator for evaluating stalk mechanical strength. The bending mechanical properties of different cultivars under different planting densities showed similar trends at pre-tasselling and dough stages, indicating the possibility of selection and evaluation for lodging-resistant maize cultivars at early developmental stage.

Key words: Maize stalk, Bending experiment, Yong’s modulus, Bending strength, Planting density