Do Forms of Silicon Other than Orthosilicic Acid, Application Date and Dose Have a Beneficial Effect on Sugar Beet Yield?

In 2017–2019, in a field experiment in Sahryń, Poland (50°40′42″ N, 23°47′35″ E), the effect of foliar application of various forms of silicon (calcium silicate—CS, sodium metasilicate—SM, and micronized silica—MS) and the timing of their application (at the 6-leaf stage of sugar beet, 7 and 14 days later) at single and double doses on physiological parameters, yield, and technological quality of sugar beet roots was studied. The silicon form significantly modified all assessed physiological parameters (NDVI, LAI, and PAR absorption) at all measurement dates. The application date had a significant effect on the assessed parameters at later measurement dates, while the product dose had essentially no effect. The silicon form significantly affected root yield and technological quality, with the exception of α-amino nitrogen content, biological sugar yield, and pure sugar yield. Foliar application of CS and SM resulted in the highest root yield, biological sugar yield, and pure sugar yield, as well as the highest sugar content and the lowest Na content in CS roots. The timing of foliar application significantly affected root yield, biological sugar yield, and α-amino N content. The highest root yield (88.53 t ha−1) and biological sugar yield (15.47 t ha−1) were achieved when the application was performed 14 days after the 6-leaf stage. Simultaneously, the technological quality of the roots deteriorated due to a significant increase in α-amino N content. Application of a double dose of the product significantly increased sugar content and decreased Na content in the roots.