Quantitative effects of solar radiation on maize lodging resistance mechanical properties

Lodging adversely affects maize (Zea mays L.) yields and quality, especially under low sunlight conditions. Here, we investigated the effects of different levels of solar radiation on maize lodging. To study the quantitative effects of different solar radiation on the lodging resistant mechanism of maize stalks, we chose two maize cultivars, Xianyu 335 (XY335) and Zhengdan 958 (ZD958), and grew them in two regions that receive the most abundant solar radiation in Xinjiang and Ningxia China in 2018 and 2019. Maize plants were exposed to different shade levels (15 % (S1), 30 % (S2), 50 % (S3), and natural light as the control (CK)) and different planting densities (4.5 x 10(4) (D1), 7.5 x 10(4) (D2), 9 x 10(4) (D3), 10.5 x 10(4) (D4), and 12 x 10(4) (D5) plants ha(-1)) to create different solar radiation conditions. The results showed that lodging percentage was significantly negatively correlated with the stalk bending strength (SBS), rind penetration strength (RPS), vertical root pulling resistance (VRPR), dry weight per unit length (DWUL), the cellulose and lignin content and grain yield which significantly decreased with decreasing total intercepted photosynthetically active radiation (TIPAR). Quantitative analysis showed that for every 1 MJ m(-2) reduction in TIPAR, the SBS and RPS decreased by 0.0667 N and 0.075 N, DWUL and the content of cellulose and lignin of maize stalk significantly decreased with decreasing TIPAR, by 0.88 mg cm(-1) , 0.3 mg g(-1 )and 0.06 mg g(-1), respectively. Lodging percentage was significantly negatively correlated with TIPAR, the lodging percentage increased by 0.17 % with a decrease in TIPAR of 1 MJ m(-2). Comparison of cultivars revealed that the rate of decrease in SBS, RPS, VRPR, DWUL and the cellulose and lignin content were greater for XY335 than for ZD958, indicating that the stalk strength of XY335 was more sensitive than ZD958 to decreasing levels of TIPAR. However, SBS, RPS, DWUL and the cellulose and lignin content of XY335 were higher than ZD938 and the lodging percentage of XY335 was lower than ZD958 which meant that XY335 had a stronger stalk strength to resistance to lodging. This is important for understanding lodging resistance and developing cultivars suited to different solar radiation conditions in different regions, as well as to changing solar radiation conditions induced by global climate change.