Effects of silicon fertilizers on lodging resistance, yield and quality of foxtail millet under different nitrogen application levels

Objective Lodging significantly affects the yield and quality of foxtail millet (Setaria italica). This study aimed to investigate the effects of silicon fertilizer on stem characteristics, yield, and quality of foxtail millet at different nitrogen levels.

Methods Field experiment was conducted in Taigu, Shanxi, two foxtail millet cultivars Jingu 21 and Zhangza 13 were selected as the experimental materials. The nitrogen application rate included conventional rate (N₁, 180 kg/hm²) and high rate (N₂, 450 kg/hm²). The silicon treatments included no silicon (Si₀), sodium silicate (Si₁, SiO₂ 68.85 kg/hm²), and silicon calcium (Si₂, SiO₂ 67.2 kg/hm²). At maturity stage, plant height, grain yield and quality, Si content in various organs, and the traits of the lowest five basal internodes, and photosynthetic characteristics were measured. The cross-seeeion structure of stems was observed using microscope.

Results Under N₁, silicon application reduced the basal internode length, increased stem diameter, stem lodging resistance, and puncture force Compared with Si₀, the internode length of the bottom five nodes of cultivar Jingu 21 and Zhangza 13 were decreased by 4.1%–30.1% and 9.5%–11.5%, and the stem thickness (i.e circumference) increased by 5.3%–19.4% and 13.0%–34.1%, respectively. Jingu 21 and Zhangza 13 were measured stronger lodging resistance under N₁-Si₁ and N₁-Si₂, respectively, the lodging resistance index of the 1st and 2nd basal node of Jingu 21 were increased by 37.4% and 35.8%, while those of Zhangza 13 were by 136.0% and 94.7%, compared to N₁-Si₀. Under N₂, silicon fertilization reduced the node length of the basal five nodes by 9.6%–30.3% and 10.6%～14.9%, and increased the stem thickness by 9.56%–23.9% and 16.2%–31.0%, and reduced the stem flatness. Si₂ treatment exhibited better promotion effect than Si₁ treatment on stem strength, N₂-Si₂ treatment enhanced the lodging resistance, puncture force, and lodging resistance index of the basal second node in Jingu 21 by 97.9%, 77.6%, and 83.3%, enhanced those of the basal first node in Zhangza 13 by 74.0%, 66.8%, and and 128%, respectively. Under microscope, the mechanical tissue of stem under Si application treatment were thicker, and more vascular bundles were formed and arranged more evenly, extending towards the center of the stem. Si application promoted the development of foxtail millet panicles, with wider panicle, more grain number and heavier thousand-grain weight. Silicon calcium increased the yields of Jingu 21 and Zhangza 13 by 23.8% and 24.0%, respectively. Further more, silicon application increased grain fat, protein, and amino acids, reduced amylose/amylopectin ratio under N₂ level.

Conclusions Under high nitrogen supply, the application of calcium silicate fertilizer reduces the length of the bottom five basal nodes, increases stem thickness and mechanical strength of foxtail millet, resulting improved lodging resistance. Simultaneously, calcium silicate application could increase photosynthetic and transpiration rate, promoting dry matter accumulation and transportation, thereby increasing grain yield and quality of foxtail millet.