Water availability in three artificial substrates during Prunus xcistena growth: Variable threshold values

In nursery plant production, optimum water use is important to maintain productivity and make this production environmentally sound. Water should be supplied when it becomes difficult to extract for the plant, at a bulk soil water potential threshold value that may vary with environmental conditions, species and substrate properties. The objective of this study was to determine the threshold value at which availability of water rapidly drops for three newly developed substrates to be used in the production of Prunus xcistena. Xylem water potential and potential at the soil-root interface were used as indices of water availability and were compared with bulk soil water potential. Water was easily available (no drop in xylem or soil-root interface water potential) from container capacity down to a bulk soil water potential of about -10 kPa when xylem water potential was used as an indicator and -8 kPa when the soil-root interface water potential was chosen as the indicator. No significant differences in the threshold values were found between substrates, consistent with the absence of differences in the substrate physical properties. The differences in water availability among substrates were consistent with an observed difference in salt content. The important variability observed in the threshold suggests that plant based measures may be preferred to soil based measures in assessing water availability in artificial mixes.