Effect of leaf removal on photosynthetically active radiation distribution in maize canopy and stalk strength

The objectives of this study were to determine how the distribution of photosynthetically active radiation (PAR) in a maize canopy affected basal internode strength and stalk lodging. The distributions of PAR within the canopies of two maize cultivars (Zhongdan 909 and Xinyu 41) were altered by removing whole leaves or half leaves in different canopy layers. The results showed that removing whole leaves or half leaves above the three-ear-leaves (R-AE and R-AE/2) at flowering significantly increased PAR at the ear and interception of PAR (IPAR) from the ear to middle of the ear and soil surface. These changes increased the structural carbohydrate content and rind penetration strength (RPS) of the third basal internode by 5.4-11.6% and reduced lodging by 4.2-7.8%. Removal of the first three leaves below the three-ear-leaves (R-BE) before flowering significantly reduced IPAR from the ear to half way below the ear. This reduced the structural carbohydrate content and the RPS of the third basal internode by 9.1-17.4% and increased lodging by 7.0-11.2%. Removal of the three lowest green leaves (R-B) in the canopy before flowering increased PAR at the bottom of the canopy, but had no effect on the structural carbohydrate content of the basal internode, the RPS, and the lodging rate. Overall, the results indicated that the key factors affecting the basal internode strength formation and lodging were PAR at the ear and IPAR from the ear to halfway below the ear. Increasing PAR at the ear and IPAR from the ear to halfway below the ear could enhance lodging resistance by increasing the structural carbohydrate content and mechanical strength of the basal internode.