Combined foliar and soil application of silica nanoparticles enhances the growth, flowering period and flower characteristics of marigold (Tagetes erecta L.)

In recent years, the utilization of nanoparticles, especially in agricultural sector, has been intensively gained the interest of policymakers and the public. Most of these nanoparticles are applied singularly through foliar or soil applications. However, no reports are highlighting the interaction between foliar and soil application of nanoparticles, particularly silica nanoparticles (SiNPs). This study reports the differences between the singular and combined (foliar and soil) applications of SiNPs on the ornamental model marigold (Tagetes erecta L.) using different concentrations of amorphous SiNPs in pot experiments carried out under open field conditions during two consecutive seasons (2017 and 2018). The results proved the potentiality of SiNPs on plant growth where all the treated plants, regardless of the SiNPs concentration and delivery technique, displayed higher values for all the measured parameters compared to the control plants. Moreover, results demonstrated that the soil application of 200 mg L-1 resulted in higher values of plant height, number of branches, and root length than the foliar application of the same SiNPs concentration. On the other hand, the foliar application of 200 mg L-1 significantly increased flower's traits over the soil application. The enhancement effect of SiNPs on plant biometrics, physiology, and properties of flower strongly linked to the Si content in plant leaves. The highest Si content corresponded to the combined foliar and soil application. Consequently, the higher number of flowers, flower's diameter, fresh and dry masses of flower, flowering period, and days taken to first bud initiation linked to plants received jointly 200 and 600 mg L-1 through foliar and soil application, respectively.