The effect of root-zone physical properties of coir and UC mix on performance of cut rose (CV. KARDINAL)

Rose plants (Rosa x hybrida L. CV. Kardinal, grafted on Natal Brier) were grown in UC mix and in coconut coir. Water release curves and hydraulic conductivity of the media were measured. Water tensions in the media were maintained within a predetermined narrow range by tension-actuated irrigation, using high-flow electronic tensiometers. Transpiration rate of plants sitting on load cells was measured between February 2 and September 8, 1999. Specific transpiration rate (STR) was calculated based on measured leaf area. Both STR and stomatal conductance were also determined using a steady-state porometer (Li-Cor 1600). Physical characteristics of the media determine water availability to plants, as reflected in STR. STR values of UC mix at water tension lower than 1.5 kPa are low, suggesting that at this tension UC Mix has insufficient free air space for proper root activity. Above 2.3 kPa, unsaturated hydraulic conductivity of UC mix is lower than that of coir. At this range, STR values may be related to the difference in hydraulic conductivity of the two media. Yield of coir-grown plants was 19% higher than that of UC mix-grown plants. It is suggested that the choice of growing medium can be optimized using detailed study of physical and hydraulic characteristics of the growing medium. Then water availability can be optimized using high-flow tensiometers or moisture content measurement, using load cells, TDR or FD sensors.