Silicon foliar spraying in the reproductive stage of cotton plays an equivalent role to boron in increasing yield, and combined boron-silicon application, without polymerization, increases fiber quality

Abstract

Foliar spraying of a boron (B) + silicon (Si) mixture (1.50 g L-1 of B + 1.15 g L-1 of Si) during the reproductive stage of cotton plants could benefit both crop yield and fiber quality; however, further research is needed to confirm this hypothesis. Two experiments were carried out under field conditions, using the FM 906 GLT cotton cultivar, with experiment I conducted in the 2018/2019 growing season and II in 2019/2020. A randomized block design was used for both experiments, consisting of four treatments: water; foliar boron; foliar silicon; and foliar boron + silicon and six replications. A preliminary laboratory test was performed to assess the turbidity of B and Si solutions and determine their compatibility in a mixture. Four foliar applications were performed, beginning in reproductive stage B1, at intervals of 7–11 days. Foliar spraying of B alone was efficient in increasing concentrations of the micronutrient in cotton leaves and fiber. Silicon foliar application was also efficient in raising concentrations in leaves and fiber. Silicon + boron proved to be efficient in supplying cotton plans with both the micronutrient and the element. The internal CO2 concentration and photosynthetic rate of plants treated with B, Si or B+Si were higher than those observed in controls, with no difference between these treatments. The addition of Si to the boron spray solution (B+Si) and Si application alone (Si) increased WUE, with no difference between these treatments, compared with B and controls. Boron, Si and B+Si increased cotton fiber yield, in relation to the control treatment. Individual and combined (B+Si) application of B and Si increased the micronaire values and cotton fiber length in both growing seasons studied. Applying only B or Si also improved the tensile strength of cotton fibers in relation to controls and the highest value for this variable in both experiments was obtained when plants were treated with the B+Si mixture. Foliar spraying of B reduced the short fiber content when compared to controls and applying Si alone or added to the boron solution produced the lowest result for this parameter. Our results demonstrate that foliar Si spraying has an equivalent effect to B on the yield and fiber quality of cotton, and that combining the two elements is particularly beneficial to cotton fiber, improving its tensile strength and reducing short fiber content.