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Stalk lodging often limits maize (Zea mays L.) grain yield potential and also causes difficulties in harvest operations. Stalk characteristics [e.g., plant height, ear height, and rind puncture strength (RPS)] have close relationships with stalk lodging in maize. The objectives of this 2-yr field study were to (i) report the changes in stalk lodging in maize cultivars that were widely grown in China since the 1950s, (ii) examine the stalk morphological and mechanical properties of maize within this timeframe, and (iii) assess the stalk lodging and grain yield of maize populations as related to changes in their stalk traits. The results showed that stalk lodging decreased significantly with the year of maize cultivar release. There was marked genotypic variation in lodging-related morphological and mechanical traits. The grain yield, dry matter accumulation (DMA), harvest index (HI), length of the 13th and 14th internodes, RPS of the fourth internode, and bending strength of the first internode all significantly increased in more modern cultivars. Length of the fourth and fifth internodes clearly decreased with improved maize cultivars. Among these traits, DMA, HI, and the length of fifth and 13th internodes were closely related to lodging resistance. As a result of stepwise regression analysis, stalk lodging was determined to be partially affected by variability in ear height or ear ratio. There were no significant correlations between stalk mechanical traits and stalk lodging. Our results indicated that improving the lodging resistance of maize cultivars was not accomplished by intentionally selecting these characteristics in China.

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Matching of maize growth with solar radiation is of great importance for achieving high yield. We conducted experiments using different maize cultivars and planting densities under different solar radiations during grain filling to quantitatively analyze the relationships among these factors. We found that a decrease in solar radiation after silking caused a drop in maize grain yield and biomass, with lower solar radiation intensities leading to worse grain yields and biomass. Cultivar ZD958 was more sensitive to solar radiation changes than cultivar XY335; slight decreases in solar radiation (i.e., 15% shading) caused significant declines in ZD958 grain yield. When total solar radiation during grain filling was less than 486.9 MJ m −2 for XY335 and less than 510.9 MJ m −2 for ZD958, the two cultivars demonstrated high yields at lower planting density of 7.5 × 10 4 plants ha −1 ; average yields were 13.36 and 11.09 Mg ha −1 , respectively. When radiation intensities were higher than 549.5 MJ m −2 for XY335 and higher than 605.8 MJ m −2 for ZD958, yields were higher at a higher planting density of 12 × 10 4 plants ha −1 , with average yields of 20.58 Mg ha −1 for XY335 and 19.65 Mg ha −1 for ZD958.

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