Effects of solar radiation on root and shoot growth of maize and the quantitative relationship between them

Solar radiation is an important environmental factor affecting maize (Zea mays L.) root and shoot growth and grain yield. This study was conducted in Qitai and Yinchuan, China, in 2018 and 2019. The maize cultivars of XY335, ZD958, and DH618 and planting densities of 7.5 x 10(4) (D1) and 12 x 10(4) plants ha(-1) (D2) were adopted under shading levels of 15 (S1), 30 (S2), and 50% (S3) with natural light as the control (CK). The results showed that averaging all shading and density treatments over the 2 yr, shading reduced the grain yields of XY335, ZD958, and DH618 by an average of 40.4, 39.2, and 35.6%, respectively, compared with the CK. The effect of solar radiation on the root dry weight was greater than that on the shoot dry weight, which resulted in a decrease in root/shoot ratio with increasing shading level. The quantitative analysis results showed that for every 1-MJ m(-2) decrease in solar radiation, the root dry weight, shoot dry weight, and root/shoot ratio decreased by 0.1938 g m(-2), 1.3517 g m(-2), and 0.0103 x 10(-2), respectively. According to this quantitative relationship, it was helpful to select cultivars and planting density with suitable root characteristics under different solar radiation conditions in different regions. From the aspects of shoot and grain yield, DH618 was more shade resistant, and its root system rapidly adjusted to compensate for shoot growth and yield formation when solar radiation decreased. Such cultivars should be given attention in future production and breeding.