Cassava growth and yield in response to rates and methods of biostimulant application

Abstract

Biostimulant application is a promising strategy for mitigating stress and enhancing yields in crops such as cassava (Manihot esculenta Crantz). However, the optimal rates and application methods for different cassava cultivars are not yet established. In this study, we aimed to evaluate the effects of the method and rate of biostimulant (Stimulate: indolebutyric acid [0.005%], kinetin [0.009%], and gibberellic acid [0.005%]) application on plant growth and storage root yield of sweet and bitter cassava cultivars. Experiment I used a 2 × 3 × 4 factorial design with four replications to test two sweet cultivars, three application methods, and four biostimulant rates (0−1200 mL ha⁻¹). A 2 × 4 factorial design with four replications and four biostimulant rates (0−1000 mL ha⁻¹) was used to test two sweet cultivars in Experiment II and two bitter cultivars in Experiment III. Biostimulant application under field conditions had limited and cultivar-dependent effects on cassava storage root development. Foliar spraying on the mother plant or stem cutting immersion was not superior to foliar spraying on young plants. Shoot growth responded positively to biostimulant (20%–29% increase) in some sweet cassava cultivars, but this did not translate to yield gains, except for a marginal increase (2.4%–16.9%) in root length or number with rates of 391–902 mL ha⁻¹. Therefore, biostimulant use cannot yet be widely adopted as a management strategy to increase cassava storage root yield, and further studies are needed to clarify cultivar- and hormone-group-specific physiological responses.