Stevia rebaudiana (Bert.) is a sweet herb native to Paraguay that contains natural noncaloric sweetener. This plant offers a solution for complex diabetic problems and obesity in humans. Worldwide demand for high-potency natural sweeteners like Stevia is expected to rise. S and W Seeds, a California alfalfa seed developer, projects that the market for Stevia is going to be upwards of £1.3 billion in 2010. This projected amount necessitates a thorough knowledge of not only the plant's nutrition but also the Stevia crop's production requirements and any associated environmental effects.
Positive Aspects of Cultivating Stevia
There are several characteristics of Stevia that make it an ideal crop to grow and may make it less environmentally harmful than other crops that are also grown for their 'sweet' characteristic or ability like sugarcane, beets or corn. Stevia is able to adapt to many climates. It is perennial and has a unique ability to recover after frost, the leaf is the harvested part and three to four harvests per year are possible, vegetative propagation is easy and intercropping is possible during the plants' initial growing period.
Fertilising and Effects
The nutrient requirements for Stevia are low to moderate; it initially adapted to poor-quality soils in its native Paraguay. When grown commercially, fertilising or manuring is recommended, if not necessary. If fertilised improperly or if too much manure is used, excess nitrogen or phosphorous may leach and have a negative environmental impact on ground or surface waters.
Stevia is a poor competitor to weeds during its initial growth period; weeds are the principle reason for limited crop establishment. For this reason, weed management plays a vital role in Stevia cultivation. Because Stevia has primarily been grown in small scale, easily managed production settings to date, traditional hand-weeding has generally been the most efficient means used to eliminate weeds. Research has found that high plant density combined with black plastic mulch provided effective weed control.
The newness of Stevia cultivation means that there has been limited research on herbicides and Stevia. Certainly as cultivation becomes more common and as monocultures, herbicides will find a role. Depending upon which herbicides are used or developed for Stevia cultivation, they may be any of a variety of effects on the environment and human health.
Stevia usually grows in locations with high soil water content. For economic Stevia crops, irrigation with quality (correct pH) water is necessary. Certainly, in places with low-soil moisture or suffering from drought conditions, the need to irrigate a Stevia crop may further exacerbate water shortage issues.
Lack of Research and Experience
The newness of large-scale Stevia cultivation means that there is a yet-to-be-developed body of work that thoroughly addresses the possible environmental effects of Stevia cultivation. Good Agricultural Practices call for the development of in-depth knowledge on water management, effects of herbicides used for Stevia crops and integrated crop management practices.