Stomatal Conductance, Growth and Yield of Pelargonium sidoides DC. in Response to Watering Frequency and Terminal Water Stress

: Water is an important factor affecting growth, yield and distribution of different species. Plant response to water deficit can be in the form of physiological disorders, such as reduction in transpiration or assimilating partitioning to root growth. Sustainable use of water has become a priority in agriculture and thus innovative irrigation management practices are critical. The study aimed at investigating how watering frequency and terminal water stress influence growth of Pelargonium sidoides , an important medicinal plant in Southern Africa. The trial was a randomized complete block design with three replicates, and treatment factors were watering frequency (everyday, twice and once a week) and terminal water stress (no watering four weeks before harvesting, no watering two weeks before harvesting and no terminal stress). There was an interacting effect of watering frequency and terminal water stress on biomass and fresh root yield. More frequent watering resulted in significantly higher biomass and fresh root yield, compared to other treatments. Watering everyday with terminal or no terminal water stress resulted in higher fresh root yield, compared to other watering treatments with terminal water stress. Plant height and leaf area were significantly affected by watering frequency and terminal water stress, respectively. A significant drop in stomatal conductance of plants watered everyday was observed 240 d after treatment implementation, such that there was no significant difference across all the three watering frequency treatments. In conclusion, farmers can save on irrigation costs by reducing watering frequency, as there was no significant difference on dry root yield.