Background: The problem of soil erosion affecting sloping agricultural land is a significant challenge globally. An estimated 36 billion tons of topsoil are lost each year because of work done to stabilize the sloping agricultural lands. Vetiveria zizanioides, commonly referred to as "vetiver grass", is gaining popularity as a low-cost bio-engineering option for slope stabilization and soil erosion control throughout diverse agroecological regions.
Objectives: The purpose of this review is to: (1) assess the morphological and mechanical characteristics of vetiver in influencing its use as a stabilizing plant species; (2) analyse how vetiver performs hydrologically and agronomically as a component of an erosion control system; and (3) evaluate the economic viability and modelling applications associated with vetiver planting for soil conservation.
Methods: A study of peer-reviewed literature spanning 30 years and 5 continents was synthesized. The parameters evaluated included: root depth, tensile strength, reduction in soil loss, runoff coefficients, effect of crop yield, and benefit-cost ratios. There were also evaluations of modeling methods using the USLE and RUSLE.
Results: The root systems of vetiver can grow 3-5 metres into the ground with tensile strengths ranging from 40 MPa to 180 MPa which surpass those of typical companion plants. The field data collected has shown a reduction in soil loss of between 46% and 83% for slopes of 5-25 degrees, with a decrease in the runoff coefficient between 40% and 60%. When vetiver is used as a strip along with contour farming the increase in crop yields was between 22%-34% and the depletion of nutrients was decreased via better retention of sediment and improved soil structure. Depending on economic analysis, the benefit/cost ratio of using vetiver was between 3.2 and 5.8, compared to normal conservation practices as reported. Finally, prior to the use of the benefits, modeling studies demonstrated that the USLE and RUSLE would be applicable to predict erosion when using the vetiver strip system; however, some uncertainties exist regarding the parameterization of root reinforcement effects.
Conclusions: Systems utilizing vetiver offer an environmentally friendly, sustainable way to prevent soil erosion through mechanical restraint, the maintenance of water patterns, and the provision of agronomic advantages. Although the evidence supporting their effectiveness is substantial, additional research will assist in developing optimal configurations for future applications of vetiver systems, improving long-term monitoring protocols, refining the parameters used to model systems, and exploring the socio-economic factors that influence a landowner's decision to adopt them.