WATER AVAILABILITY IN 3 ARTIFICIAL SUBSTRATES DURING PRUNUS X CISTENAGROWTH - VARIABLE THRESHOLD VALUES

In nursery plant production, optimum water use is important to maintai n productivity and make this production environmentally sound. Water s hould be supplied when it becomes difficult to extract for the plant, at a bulk soil water potential threshold value that may vary with envi ronmental conditions, species and substrate properties. The objective of this study was to determine the threshold value at which availabili ty of water rapidly drops for three newly developed substrates to be u sed in the production of Prunus x cistena, Xylem water potential and p otential at the soil-root interface were used as indices of water avai lability and were compared with bulk soil water potential. Water was e asily available (no drop in xylem or soil-root interface water potenti al) from container capacity down to a bulk soil water potential of abo ut-10 kPa when xylem water potential was used as an indicator and -8 k Pa when the soil-root interface water potential was chosen as the indi cator. No significant differences in the threshold values were found b etween substrates, consistent with the absence of differences in the s ubstrate physical properties. The differences in water availability am ong substrates were consistent with an observed difference in salt con tent. The important variability observed in the threshold suggests tha t plant based measures may be preferred to soil based measures in asse ssing water availability in artificial mixes.