Characterisation of plant water stress of greenhouse tomatoes (Lycopersicon esculentum) grown hydroponically in coir
Only by characterising the growth medium's water retention characteristics and ability to supply water, can the irrigation technique for coir be improved. The study was conducted to describe the development of water stress of greenhouse tomatoes grown in coir, to identify different stages of water stress, and to determine the implication for irrigation management. From this study, mild water stress started as soon as the volumetric water content dropped below that of the well-watered mediums and lasted while the plant conditioned to the water stress. The onset of moderate water stress occurred from the point where the cucumber plants do not recover under continuous drying of the medium. Increased leaf water potential, stomatal resistance and the first signs of wilting confirmed moderate crop water stress. Severe water stress occurred where changes in the slope of transpiration of unwatered plants divided by reference transpiration became negligible over time and about 75% of all plants were irreversibly wilted. Based on plant response only, water depletion can be allowed to a point before moderate water stress is reached. Soil water sensors calibrated to measure volumetric water content in coir or tensiometer measurements converted to volumetric water content from a laboratory-determined retention curve for coir may be used to trigger irrigation.